12th Standard CBSE Physics CBSE - study material, free online tests, previous year question papers, answer keys, topper answers, centum question paper, exam tips

CBSE 12th Physics Wave Optics Chapter Case Study Question with Answers - by users_admin - Jan 22, 2024 - View & Read

CBSE 12th Physics Ray Optics and Optical Instruments Chapter Case Study Question with Answers - by users_admin - Jan 22, 2024 - View & Read

CBSE 12th Physics Nuclei Chapter Case Study Question with Answers - by users_admin - Jan 22, 2024 - View & Read

CBSE 12th Physics Moving Charges And Magnetism Chapter Case Study Question with Answers - by users_admin - Jan 22, 2024 - View & Read

CBSE 12th Physics Electromagnetic Induction Chapter Case Study Question with Answers - by users_admin - Jan 22, 2024 - View & Read

CBSE 12th Physics Atoms Chapter Case Study Question with Answers - by users_admin - Jan 22, 2024 - View & Read

12th Physics Alternating Current Chapter Case Study Question with Answers CBSE - by users_admin - Jan 13, 2024 - View & Read

CBSE 12th Standard Physics Subject Wave Optics Value Based Questions 5 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
When puja, a student of 10th class, watched her mother washing clothes in the open, she observed coloured soap bubbles and was curious to know why the soap bubbles appear coloured. In the evening when her father, an engineer by profession, came home, she asked him this question. Her father explained to her basic phenomenon of physics due to which bubbles appear coloured.
(a) What according to you are the values are the displayed by puja and her father?
(b) State the phenomenon of light involved in the formation of coloured soap bubbles.
2)
Anil is using yellow light in a single slit diffraction experiment with of 0.6 mm. When his friend replaced yellow light by X-rays then diffraction pattern is not visible.they became surprised and asked the teacher about such thing.The teacher replaces X-rays by yellow light and diffraction pattern appears again. The teacher explained all the facts about diffraction properly.
(a) What are the values noticed in both the students?
(b) Give the necessary condition for the diffraction?
(c) Why is diffraction pattern not visible by using X-rays in such case?
3)
Two students are situated in a room 10 m high, they are separated by 7 m high partition wall. the students are unable to see each other even though they can converse easily. But they know that both light and sound waves can bend around the obstacles. So they were phenomena. Then they went to their friend Neelam who convinced them with basic facts.
(a) what are the values shown by Neelam?
(b) How did Neelam convince them such basic facts?
4)
During summer vacation Radha and Rani decided to go for a 3 FILM. They have heard about this film through their friends. They were asked to buy special glasses to view the film. Before they go for a movie, they approached their Physics teacher to know about these glasses. Physics teacher explained when two polarizer's are kept perpendicular to each other (crossed polarizer's), the left eye sees only the image from the left end of the projector and the right eye sees only the image from the right lens. The two images have the approximate perspectives that the left and right eyes would see in reality the brain combine the image to produce a realistic 3-D effect
(a) What qualities do these girls possess?
(b) What do you mean by polarization?
(c) Mention the other applications of polarization.
5)
School arrange an educational trip to Kavalur in Tamil Nadu where an observatory having Indias largest telescope. On hearing this, the whole class got excited and left for their way to kavalur. In the observatory, the physics teacher' was explaining about the type of telescope, with diameter of objective (2.34 m) and several other details. Everyone was ready to look through the telescope.
(i) What type of telescope is the teacher referring to?
(ii) Mention any two advantages of this telescope
(iii) Why are such a field trips important?

CBSE 12th Standard Physics Subject Wave Optics Value Based Questions 5 Mark Questions 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
Mr.Vishwanathan, a retired professor of physics was walking with his grandson. It was last week of December and it was drk aruond 5.30 pm. The streetlights were on and the yellow light flooded the area around. The boy asked professor why yellow lights were used when light was beighter. The professor answered that during foggy days the tiny droplets act as prisms splitting white light light into its constituwnt colours and thus reducing the clarity.
Read the above passage and give the answer of the following questions:
(i) What phenomenon was the professor referring to? Why does it happen?
(ii) Give one application of prism.
(iii) What values of the boy are being reflected from the conversation?
2)
Kanchan while driving her scooty sees a woman behind driving a moped through his rear view mirror. She sees that her saree is almost touching the wheels of the vehicle. She stops her and alert that it may cause a severe accident.
Read the above passage and answer the folllowing questions:
(i) What values do you observe in Kanchan?
(ii) Name the mirror used in rear view in scooty. Draw a ray diagram for the same.
3)
Kritika's mom is finding difficult to cook in the kitchen as there was power-cut and she told the same to Kritika. She immediately took a plane mirror from her shelf made it stand against a wall such that sun rays were focussed into the Kitchen due to the reflection of the mirror. There was some lighting and her mother was able to finish her work.
Read the above passage and answer the following question:
(i) What are the values shown by Kritika?
(ii) Name the types of mirror used in periscope.
(iii) Give the nature of image in case of plane mirror.
4)
One day, Chetan's mother developed a sever stomach ache all of a sudden. She immediately rushed to the doctor, who suggested for an immediate endoscopy test and gave an estimate of expenditure for the same. Chetan immediately contacted his class teacher and shared the information with her. The class teacher arranged the money and reached to the hospital. On realising that Chetan belonged to a below average incom group of family, even the doctor offered concession for the test fee.The test was conducted successfully.
Read the above passage and answer the following questions:
(i) Which principle of optics is used in endoscopy?
(ii) Briefly explain the values reflected in the action taken by the teacher.
(iii) In what way do you appreciate the response of the doctor on the given situations?
5)
Ravi wanted to buy a gift for his sister and so he entered inside a gift shop. The gift shop had many glass items. On looking closely, he found many of the beverage glasses used for cold drinks had big thick glass walls. He decided not to buy these glasses because he knows that this gives a false impression that there is more amount of liquid inside the glass.
Read the above passage and answer the following questions:
(i) How does Ravi know about the false impression given by the beverage glasses made with very thick glass walls?
(ii) What values can you associate with Ravi decision?

CBSE 12th Standard Physics Subject Communication Systems Value Based Questions 5 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
Mohan went to the market to purchase a TV set. He got confused with so many features and functions of electronic appliances. He took the help of his friend Sohan, a science student.Sohan explained him about the communication system, digital and analog signals. This knowledge proved of great help to Mohan in purchasing a colour TV.
Read the above passage and the answer the following questions:
(i) What do you mean by the term communication?
(ii) Which type of signals are better?
(iii) What type of nature Sohan has?
(iv)What is the minimum number of communication satellites required for global communication coverage?
2)
In the famous conversation, Rakesh Sharma, the first Indian Astronaut in space, was asked by the Prime Minister Indira Gandhi as to how India looked from space.To which he replied,'Sare Jahan Se Achcha' (better than the whole world).
Read the above passage and answer the following questions:
(i) Which scientific mode of communication enabled the Prime Minister to speak to the Astronaut?
(ii) Name the scientific values displayed in this anecdote.
(iii) Which values are being reflected in the reply given by the astronaut?
(iv) Give one more example of this scientific mode of communication in everyday life situations.
3)
Raj was cycling from his village to a neighbouring village.On the way, he met an old man who was walking in the direction of the same neighbouring village. Raj invited the old man to sit on his cycle and took him to the neighbouring village.The old man got down from the cycle, thanked Raj and gave him blessing.
Read the above passage and answer the following questions:
(i) What are the values displayed by Raj?
(ii) Can you relate the given paragraph with the process of modulation?
4)
Group discussion was arranged in class XII on the topic of atmosphere. Three groups were made. Teacher asked the question "why can Moonbe not used as a communication satellite?" Answers were given by all the three groups. Each, group can give only one reason. Teacher told them that reason given by each group is correct. The groups collected all the three, reasons and came to correct conclusion,"
(i) Give the correct reason for the above question.
(ii) What values were showed by all the three groups?

CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits Value Based Questions 5 Mark Questions With Solution - by Sharma - Kochi - May 31, 2021 - View & Read

1)
\(p-n\) junction is a semiconductor diode.It is obtained by bringing \(p-\) type semiconductor include contact with \(n-\) type semiconductor. A thin layer is developed at the \(p-\) junction which is devoid of any charge carrier but has immobile ions. It is called depletion layer. At the junction a potential barrier appears, which does not allow the movement of majority charge carriers across the junction in the absence of any biasing of the junction.
\(p-\)n junction offers low resistance when forward biased and high resistance when reverse biased. Read the above paragraph and answer the following questions:
(i) Can we measure the potential barrier of \(p-n\) junction by putting a sensitive voltmeter across its terminals?
(ii) What practical lesson do you draw from the above study?
2)
Kritika Singh was enjoying TV programme at her home with her younger brother Surya at night. Suddenly, the light went off causing darkness all over. Surya asked her to bring candle along with matchstick to put the TV switch OFF. Kritika at once picked the mobile phone and pressed the button lighting up the surrounding. Her younger brother was surprised and asked, where the light was coming. Kritika proudly showed her mobile.
Read the above passage and answer the following questions:
(i) Which value is displayed by Kritika?
(ii) Name the material used in the formation of LED.
(iii) LED works, in which biasing?
3)
Ashwin was given 3 semiconductors A, B, and C with respective band gaps of 3 eV, 2 eV and 1 eV for use in a photodetector to detect \(\lambda =1400\quad nm.\) He found that the photodetector was not working with these semiconductor and did not know. Why? his friend Akash found out the reason for it and explained it to him. Read the above passage and answer the following questions:
(i) Why did the photodetector not work?
(ii) What according to you are the values shown by Akash?
4)
Shorya usually enjoyed loud music. One day his music system was not producing very loud sound. Shorya gets disappointed. He discussed his problem with his big brother Kamal. Kamal advised him to connect an amplifier in series with the amplifier of the stereo system. This increased the sound of Shroya's music system considerably. Read the above passage and answer the following questions:
(i) Which value is displayed by Kamal?
(ii) Why the loudness of music system get increased on connecting amplifier?
(iii) Give the equation for current gain in the transistor as an amplifier.
5)
Khusbhu Mowar is an electronic engineer. She was working in a project for college exhibition. Her younger sister asked Khushubu about a small black coloured device. which Khusbhu was working on. She clearly explained the working of integrated circuit(I_C) to her sister. Read the above passage and answer the following questions:
(i) What according to you, are the values displayed by Khusbhu?
(ii) What is an integrated circuit? What are the uses of the integrated circuit?
(iii) What do you mean by microprocessor?

CBSE 12th Standard Physics Subject Nuclei Value Based Questions 5 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
A nuclear reactor is a powerful device, wherein nuclear energy is utilised for peaceful purposes. It is based upon controlled nuclear chain reaction. The nuclear chain reaction is controlled by the use of control rods (of boron or cadmium) and moderators like heavy water, graphite, etc. The whole reactor is protected with concrete walls 2 to 2.5 metre thick, so that radiations emitted during nuclear reactions may not produce harmful effects.
Read the above passage and answer the following questions:
(i) Give any two merits of nuclear reactors.
(ii) What is radiactive waste?
(iii) Why do people often oppose the location site of a nuclear reactor? What do you suggest?
2)
Einstein was the first to establish the equivalence between mass energy. According to him, whenever a certain mass \(\left( \Delta m \right) \) disappears in some process, the amount of energy released is \(E=\left( \Delta m \right) { c }^{ 2 },\) where c is velocity of light vacuum \(\left( =3\times { 10 }^{ 8 }m/s \right) .\) The reverse is also true, i.e., whenever energy E disappears, an equivalent mass \(\left( \Delta m \right) ={ E/c }^{ 2 }\) appears.
Read the above passage and answer the following questions :
(i) What is the energy released when 1 a.m.u. of mass disappears in a nuclear reaction?
(ii) Do you know any phenomenon in which energy materialises?
(iii) What values of life do you learn from this famous relation?
3)
Poonam's mother is diagnosed cancer. The attending physician told her that she has to undergo radiotherapy. While telling her the side effects of the treatment, the doctor told that her beautiful hair may fall and she may become bald. Poonam's mother refuses to get the treatment.
Read the above passage and answer the following questions:
(i) What would you do if you were in Poonam's place?
(ii) What values are associated with your attitude?
4)
Marie Curie and her teacher turned husband Pierre Curie worked hard to extract radium chloride (R_aCl₂) from uranium ore. They succeeded in 192 after a long struggle. About 0.19 g of R_aCl₂ was extracted and its radioactivity was studied. They were awarded by the noble prize, which they shared it which they shared it which they shared it with Henri Becquerel.
Read the above passage and answer following questions:
(i) What are the values shown by Marie Curie and her husband?
(ii) What do you understand by radioactivity? How the half-life period is related to the disintegration constant?
(iii) How is average-life of radioactive element related to half-life?
5)
Shyamsaw his younger brother wondering with a question which deals with emission of light from a vapour lamp. He was anxious to know how different colours wre being emitted by different lights. He also saw mercury and sodium vapour lamps in the Physics lab and was curious to know what is inside the lamps. On seeing his anxiety to know more about it, Shyam explained about absorption of energy and re-emission of photons in the visible region. He also advised him not to touch or break any items in the lab for the knowledge.
Read the above passage and answer the following questions:
(i) What is the moral you derive from Shyam's behaviour?
(ii) Which series in the hydrogen spectrum is in the visible region?
(iii) Write the quality displayed by Shyam's brother.

CBSE 12th Standard Physics Subject Atoms Value Based Questions 5 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
Nuclear fission is the phenomenon of splitting of a heavy nucleus into two or more lighter nuclei. Nuclear fussion is the phenomenon of fusing two or more lighter nuclei to form a single heavy nucleus. In both these processes, a certain mass \(\left( \Delta m \right) \) disappears, which appears in the form of nuclear energy, \(E=\left( \Delta m \right) { c }^{ 2 }.\) The release of energy is so sudden that it cannot be controlled. This causes havoc. Nuclear fission is the basis of an atom bomb and nuclear fusion is the basis of a nydrogen bomb. A powerful device, called Nuclear Reactor has been developed, where in nuclear energy produced is utilised for constructive purposes.
Read the above passage and answer the following questions:
(i) How much energy is released in the fission of one nucleus of \({ U }^{ 235 }\) and in how much time?
(ii) Give an estimate of devastation potential of an atomic explosion.
(iii) Should we ban nuclear research in this field? Give your views briefly.
2)
Natural radioactivity is a spontaneous and self disruptive activity exhibited by a number of heavy elements in nature. Thus a heavy element disintegrates by itself without being forced by any external agent to do so.
According to radioactive decay law, the number of atoms disintegrated per second (i.e., rate of disintegration of radioactive atoms) at any instant is directly proportional to the number of radioactive atoms actually present in the sample at that instant, i.e., \(-\frac { dN }{ dt } \propto N \ or \ R=-\frac { dN }{ dt } =\lambda N,\) where is \(\lambda \) decay constant.
Read the above passage and answer the following questions :
(i) The count rate from a radioactive sample containing \({ 10 }^{ 16 }\) atoms is \(4\times { 10 }^{ 16 }\) per second. What is the value of decay constant?
(ii) Name the three types of radiactive radiations. Which one of them is most penetrating?
(iii) What does radioactive decay law imply in day to day life?
3)
According to Bohr's theory of hydrogen atom, total energy of electron in a stationary orbit is \(E=-\frac { 13.6 }{ { n }^{ 2 } } eV,\) where n is the number of orbit. Clearly, total energy of electron in a stationary orbit is negative, which means the electron is bound to the nucleus and is not free to leave it. An n increases, value of negative energy decreases, i.e., energy is progressively larger in the outer orbits.
Read the above passage and answer the following questions :
(i) What is total energy of electron in ground state of hydrogen atom? What does it imply?
(ii) Energy required to remove an electron is smaller when atoms is in any one excited state. Comment.
(iii) How is this concept translated in day to day life?
4)
Ajeet's younger brother was just seeing class 12th books. He wondered to know the structure of atoms and arrangement of electrons and protons in them. As he was a class 6th student, he did not understand the whole concept of atomic structure. Ajeet helped him to understand the structure of atoms.
Read the above passage and answer the following questions:
(i) What are the values shown by Ajeet?
(ii) On which metal Rutherford performed \(\alpha \) - particles scattering experiment?
(iii) How Rutherford concluded that at the centre of atom there is massive nucleus which contains positive charge?
5)
On the basis of Bohr's theory of H-atom, total energy of electron in a stationary orbit is given by the relation
Where, n is the number of orbits. It is clear that total energy of electron in a stationary orbit is negative which implies that electron is bound to the nucleus and is not free to leave it. The value of negative energy decreases as n increases.
Read the above p[assagr and answer the following questions:
(i) What is the total energy of electron in ground state of hydrogen atom? What does it indicate?
(ii) Why does energy required to remove an electron is smaller when atom is in any one excited state?

CBSE 12th Standard Physics Subject Dual Nature of Radiation and Matter Value Based Questions 5 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
Work function of a metal is the minimum amount of energy required by an electron to just escape from the metal surface without any kinetic energy. The expression for work function of metal is
\({ \phi }_{ 0 }={ hv }_{ 0 }=hc/{ \lambda }_{ 0 }\)
where h is Plank's constant;v₀ is the threshold wavelength and c is the velocity of light in vacuum.
(i) Why different metals has different work function?
(ii) What is the threshold wavelength of the incident radiation for a metal surface whose work function is 1.2 eV. Given \(h=6.63\times { 10 }^{ -34 }Js;\)\(1eV=1.6\times { 10 }^{ -19 }J\)
(iii) What do you learn from this study?
2)
Radiation has dual nature,i.e., it possesses the properties of both; wave and particle.This prompted de-Broglie to predict dual nature of moving material particles.Thus waves are associated with moving material particles which are called matter waves. The wavelength of matter wave is given by \(\lambda =\frac { h }{ mv } \), where m is the mass, v is the speed of the particle and h is Plank's constant. Read the above paragraph and answer the following questions;
(i) How was the wave nature of the electron established?
(ii) What are the de-Broglie wavelength associated with a particle (i) at rest (ii) moving with infinite speed?
(iii) What are the basic values displayed with this study?
3)
According to Plank's constant quantum theory of light, every source of radiation emits photons(i.e., packets of energy) which travel in all directions with the same speed (i.e., speed of light). Each photon is of energy \(E=hv=\frac { hc }{ \lambda } \) where h is plank's constant, v is the frequency and \(\lambda \) is wavelength of radiation emitted. The photons emitted from different sources of radiation are different.
Read the above passage and answer the following questions:
(i) On what factors does the number of photons emitted per second from a source of radiation depend?
(ii) Why are the high energy photons not visible to eye?
(iii) Which basic values do you learn from this study?
4)
"Know your face beauty through comp[lexion meter" was one of the stall on science exhibition. A student interested to know his/her face beauty was made to stand on a platform and light from a lamp was made to fall on his/her face. The reading of complexion meter indicated the face beauty of the student which might be very fair, fair,semi-fair, semidark dark etc.
(i) What is the basic concept used in the working of complexion meter?
(ii) How is the face beauty recorded by face complexation meter?
(iii) What basic values do you learn from the above study?
5)
The photoelectric effect is a phenomenon of emission of electrons from the surface of a metal when the light of suitable frequency falls on it.
If light of frequency v falls on a photosensitive surface of work function increases or work function then the maximum kinetic energy of photoelectric emitted is given by Einstein's photoelectric equation.
\({ (KE) }_{ max }=\frac { 1 }{ 2 } { { mv }^{ 2 } }_{ max }=hv-{ { \phi }_{ 0 } }\)
The value \({ (KE) }_{ max }\) will increase if the energy of the incident light(hv) increases or work function \({ { \phi }_{ 0 } }\) is decreased.
Read above passage and answer the following questions:
(i) Why can visible light not eject photoelectrons from every metal surface?
(ii) Light of frequency \(7.21\times { 10 }^{ 14 }Hz\) is incident on a metal surface.Electrons with a maximum speed of \(6.0\times { 10 }^{ 5 }{ ms }^{ -1 }\) are ejected from the surface. What is the threshold frequency for photo emission of electrons?\(h=6.63\times { 10 }^{ -34 }Js;\ { m }_{ e }=9.1\times { 10 }^{ -31 }kg\)
(iii) What do you learn basically from the above study?

CBSE 12th Standard Physics Subject Electromagnetic Waves Value Based Questions 5 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
Mr.Kamal and Jayant were playing football in the ground. In the middle of the match, Kamal fell down as there was a cramp in his right leg. Jayant rushed towards him and picked him up and told him not to move. They went to the nearby hospital.Doctor examined his legs and advised for an X-ray test for the confirmation of fracture.
(i) What are the values Jayant show here?
(ii) How are X-rays produced?
(iii)Can you give one other application of X-ray?
2)
Shyam and his younger brother were at the restaurant. It was very clean there. None of the flies and insects were there. His younger brother asked him about the fluorescent UV lamp present at the corner. Shyam explained the functioning of UV lamp, how flies and insects get trapped by it?
(i) What are the values shown by Shyam?
(ii) Give the source of UV-rays.
(iii)Give the harmful effect of UV-rays.
3)
Two friends went on an excursion on a hill top where temperature was quite low. One of them fell ill.The other one put a blanket on him, collected the pieces of dry wood and ignited fire in his vicinity. After sometime the ill friend felt better.
(i) What are the type of EM waves coming from fire?
(ii) Why did the ill friend feel better after sitting rear the fire?
(iii) What basic values do you learn from this study?

CBSE 12th Standard Physics Subject Moving Charges And Magnetism Value Based Questions 5 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
Two linear parallel conductors carrying currents in the same direction attract each other and two linear parallel conductors carrying in opposite directions repel each other. The force acting per unit length due to currents \({ I }_{ 1 }and{ I }_{ 2 }\)in two linear parallel conductors held distance r apart in vacuum in SI unit is \(F=\frac { { \mu }_{ 0 } }{ 2\pi } \frac { 2{ I }_{ 1 }{ I }_{ 2 } }{ r } \)
Read the above passage and answer the following questions:
(i) What is the basic reason for the force between two linear parallel conductors currents?
(ii) Two straight wires A and B of lengths 2 cm and 20 cm, carrying currents 2.0 A and 5.0 A respectively in opposite directions are lying parallel to each other 4.0 cm apart. The wire A is held near the middle of wire B. What is the force on 20 cm long wire B?
(iii) What does this study imply in day to day life?
2)
When a galvanometer of resistance G is shunted with a low resistance S, then the effective resistance \({ Re }_{ ff }\)of galvanometer becomes
\( { Re }_{ ff }=\frac { GS }{ G+S } \)
If the current is passed through such a galvanometer, then the major amount of current flows through the shunt and the rest through the galvanometer, then the major amount of current flows through the shunt and the rest through galvanometer., the current divides itself in the inverse ratio of resistances.
Read the above passage and answer the following questions:
(i) Why is the resistance of shunted galvanometer lower than that of a shunt?
(ii) A galvanometer of resistance.\(30\Omega \) What the fraction of the main current passes (i) through the galvanometer and (ii) through the galvanometer and (ii) through the shunt?
(iii) What are the basic values you learn from the above study?
3)
Saniya and Priya are friends. Both of them know that a small compass needle point always along north-south direction. One day Saniya is plotting field due to a bar magnet in the laboratory. She discovers a point where compass needle does not point along N-S. Rather, it sets itself in any arbitrary direction. Saniya thinks first that compass needle has become faulty. Priya then explains to her the real situation.
Read the above passage and answer the following questions:
(i) How did Priya justify the situation?
(ii) If a bar magnet is placed along the N-S direction with its north pole pointing north, what is the position of neutral points?
(iii) If a bar magnet is placed along N-S direction with its north pole pointing South, What is the position of neutral points?
(iv) What values of life do you learn from this piece of knowledge?

CBSE 12th Standard Physics Subject Current Electricity Value Based Questions 5 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
That night Vaikunth was preparing for his physics exam. Suddenly, the light in his room went off and he could not continue his studies. His cousin brother Vasu who had come to visit him was quick to react. Vasu using the torch (an android application) installed in his mobile phone found that the fuse had blown out. He checked the wiring and located a short circuit. He checked the wiring and located a short circuit. He rectified it and put a fuse wire. The light came to life again. Vaikunth had a sign of releif and continued his studies.
Read the above passage and answer the following question.
(i) What are the values projected by Vaikunth and Vasu?
(ii) Why did Vasu have to check the wiring?
(iii) What is an electric fuse? What characteristics you would prefer for a fuse wire?
2)
Ramaniamma was a childless window. She ran her life only by the pension for the Sr. citizens from the Government. When she switches ON one bulb in her house, all the other appliances get switched OFF. She could not even spend for an electrician. Sujatha living nearby decided to do something for her. She referred to Physics books and learned that the series combination for the household connection could be the reason. She called an electrician and had the circuit changed to parallel combination. The problem was solved and Ramaniamma was happy. She thanked Sujatha for her help to solve the problem.
Read the above passage and answer the following questions.
(i) What are the values possessed by Sujatha?
(ii) Why a parallel combination is used for household? Give two advantages.
3)
Vishwajeet purchased cells for his transistor. He felt that cells are not working properly. He wanted to check their emf. So, he took the cells to the physics lab and with the help of potentiometer found their emf. To his surprise, emf was less than the value claimed by the manufacturer. He lodged the complaint with consumer forum and received the deserving response.
Read the above passage and answer the following question.
(i) What values are displayed by Vishwajeet?
(ii) Why do you think Vishwajeet used potentiometer instead of voltmeter to find out emf of the cell? For more precise measurement, the potential gradient of the potentiometer should be high or low?
4)
The unknown resistance of a conductor can be determined by Wheatstone bridge. The standard form of Wheatstone bridge is shown in the figure. It can be shown when the bridge is balanced.

\(\frac { P }{ Q } =\frac { R }{ S } \quad or\quad S=\frac { Q }{ P } R\)
Knowing P,Q and R, unknown resistance S can be calculated.
Read the above passage and answer the following questions.
(i) Name any two applications of Wheatstone bridge.
(ii) What is the practical utility of the post office box in day to day life?

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Value Based Questions 5 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
When an electric dipole of moment \(\left| P \right| \) = q \(\times\) 2a is held at an angle \(\theta\), with the direction of uniform external electric field E, a torque \(\tau \) = pE sin\(\theta\) acts on the dipole. This torque tries to align the electric dipole in the direction of the field. When p is along E, \(\theta=0^{o}\), \(\tau \) = pE sin\(0^{o}\) = zero.

Read the above passage and answer the following questions.
(i) What is the direction of torque acting on an electric dipole held at a angle with uniform external field?
(ii) An electric dipole of length 10 cm having charge \(\pm 6\times { 10 }^{ -3 }\), C placed at \(30^{o}\) with respect to a uniform electric field experiences a torque of magnitude \(6\sqrt { 3 } \) N-m. Calculate magnitude of electric field.
(iii) What is the physical significance of this concept in our day-today life?
2)
Two persons are standing under a tree and another person near them is inside a car. They were arguing about going out for a movie or to the beach, when a lightning struck the tree with some force. The person inside the car notices his friends satnding under the tree are affected by lightning, he comes out and takes them to the nearby hospital.
Why the person in the car was not affected by lighting?
What quality do you find the person inside the car?
Explain the process that takes place during lighting.
If the total charge enclosed by a surface is zero, then what will be the electric flux over the surface?
3)
The surface integral of electrostatic field E produced by any source over any closed surface S enclosing a volume V in vacuum, i.e. total electric flux over the closed surface S in vacuum is \(1/{\epsilon}_{0}\) times the total charge Q contained inside S, i.e.
\({\phi}_{E}=\oint E.dS={{Q}\over{{\epsilon}_{0}}}\)
The charges inside S may be point charges or even continuous charge distributions. There is no contribution to "total electric flux from the charges outside S. Further, the location of Q inside S does not affect the value of surface integral.
Read the above passage and answer the following questions
What are the SI units and dimensions of electric flux?
A closed surface in vacuum encloses charges -q, + 3q and +5q. Another charge + 4q lies outside the surface. What is total electric flux over the surface?
A point charge a lies inside a spherical surface of radius r. How will the electric flux be affected, if, radius of the sphere is doubled?
What values of life do you learn from this theorem?
4)
An old woman who had suffered from a heat stroke was taken to the hospital by her grandson who is in class XII. The grandson has studied in Physics that, how to save person who is suffering from a heat stroke, regular beating of the heat is to be restored by delivering a jolt to the heart using a defibrillator, whose capacity is 70 μF and charged to a 'potential of 5000 V and energy stored is 875 J, 200 J of energy is passed through a person's body in a pulse lasting 2 ms. The old woman gets paniced and refuses to be treated by defibrillator. Her grandson then explained to her the process that would be adopted by medical staff and how the result of that would bring her back to normalcy. The woman was then treated and was back to normal. Answer the following questions based on the above information.
(i) What according to you are the values displayed by the grandson?
(ii) What will be the net charge of the capacitor in defibrillator?
5)
A man travelling in a car during heavy rain and thunderstorm, sees a boy standing under a tree. He immediately stops his car and asks the boy to get inside the car and saves him from a possible natural calamity. Answer the following questions based on the above information.
(i) What danger did the boy had while standing under the tree during the thunderstorm?
(ii) How is it safer inside the car during such weather?
(iii) What according to you are the values displayed by the man to help the boy?
(iv) Give another example from everyday life situations which represent display of similar values.

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Value Based Questions 5 Mark Questions 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
A rectangular coil of n turns each of area A, carrying current I, when suspended in a uniform magnetic field B, experiences a torque
\(\tau =nI \ BA \ sin\theta \)
Where is \(\theta \) the angle which a normal drawn on the plane of coil makes with the direction of magnetic field. This torque tends to rotate the coil and bring it in an equilibrium position. In the stable equilibrium state, the resultant force on the coil is zero. The torque on the coil is also zero and the coil has minimum potential energy.
Read the above passage and answer the following questions:
(i) In which position, a current carrying coil suspended in uniform magnetic field experiences
(a) minimum torque and
(b) maximum torque?
(ii) a circular coil of 200 turns, radius 5 cm carries a current of 2.0 A. It is suspended vertically in a uniform horizontal magnetic field of 0.20 T, with the plane of the coil making an angle with \(60°\) the field lines. Calculate the magnitude of the torque that must be applied on it to prevent it from turning.
(iii) what is the basic value displayed by the above study?
2)
Shikhaj was working on a project for science exhibition. He considered a capacitance of 2\(\mu F\) having a capacity of operating under 1kV potential. When he reached to shop, he found that the shopkeeper is having a capacitors of 1 \(\mu F\) of 400 V rating. Shikhaj calculated minimum number of capacitances of 1 \(\mu F\) each, so he could arrange to form a capacitor of 2 \(\mu F\) .
Answer the following questions based on the above information:
(i) What are the calculations done by Shikhaj?
(ii) What do you think of Shikhaj?
3)
In Pradeep's classroom, the fan was running very slowly. Due to which, his teacher was sweating and was restless and tired.All his classmates wanted to rectify this. They called an electrician who came and changed the capacitor only, after which the fan started running fast.
Answer the following questions based on the above information:
(i) What energy is stored in the capacitor and where?
(ii) A thin metal sheet is placed in the middle of a parallel plate capacitor. What will be the effect on the capacitance?
(iii) What values did the classmates have?
4)
Geeta has dry hair. A comb ran through her dry hair attracts small bits of paper. She observes that Neeta with oily hair combs her hair, the comb could not attract small bits of paper. She consults her teacher for this and gets the answer. she then goes to the junior classes and shows this phenomenon as a Physics experiment to them.
Read the above passage and answer the following questions.
What according to you are the values displayed by Geeta?
Explain the phenomenon involved.
5)
As it is known that all matter is made up of atoms/ molecules. Every atom consists of a central core, called the atomic nucleus, around which negatively charged electrons revolve in circular orbits. Every atom is electrically neutral containing as many electrons as the number of protons in the nucleus. All the materials are electrically neutral, they contain charges, but their charges are exactly balanced.
Read the above passage and answer the following questions.
Everybody whether a conductor or an insulator is electrically neutral. Is it true?
Charging lies in charge imbalance, i.e. excess charge or deficit charge, comment.
How do you visualise this principle being applied in our daily life?

CBSE 12th Standard Physics Subject Wave Optics Value Based Questions 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
Sumeet a 5^th class student observed a coloured film of oil on water when illuminated by white light. He felt happy and surprised to see this. His teacher explained him the reason behind it. The child then gives an example of spreading of kerosene oil on water to prevent malaria and dengue.
(i) What value was displayed by his teacher?
(ii) Name the phenomenon involved.
2)
Ravi is using yellow light in a single slit diffraction experiment with slit width of 0.6mm. The teacher has replaces yellow light by x-rays. Now he is not able to observe the diffraction pattern. He feels sad. Again he teacher replaces x-rays by yellow light and the diffraction pattern appears again. The teacher now explains the facts about the diffraction and
Which value is displayed by the teacher.
Give the necessary condition for the diffraction.
3)
Two boys, on their way from school were discussing seriously about something. They both were blowing soap bubbles and were thrilled to watch the expanding bubble with spectacular colour rings. Rita, a class XII student, was watching them for a long time, walking behind them. Suddenly she realised that the kids did not look at the traffic in that junction area. She rushed to them and instructed them to be cautious while on the road. She also explained the importance of traffic rules and told them that obeying traffic rules not only makes us safe but also others safe.
(i) What are the values highlighted by Rita
(ii) why are colours formed on bubbles?

CBSE 12th Standard Physics Subject Communication Systems Value Based Questions 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
Arun lives in Delhi, His grandfather lives in a small village in Haryana.He always misses his grandfather, so he decided to purchase a mobile phone for his grandfather.He saved his pocket money and purchased the mobile phone.Now his grandfather communicates often with his family and now they are happy.
(a) What are the values Arun displayed in his act?
(b) Name the type of wave used in mobile communication.Write its frequency range.
2)
Rita was studying in 10th class, one day she asked her father to explain the working of remote control of TV. Her father was not knowing the answer, but he made up his mind to understand the working of remote control. He found one shop where remote controls were repaired. The shopkeeper showed to Rita's father the inside of the remote control and explained her the working. Rita's father explained her the working of remote control, Rita was happy and satisfied.
(a) What are the values Rita's father displayed in his act?
(b) Name the diode used in remote control.
3)
Modulation is the phenomenon of superimposing the low audio frequency base band message or information signals (called the modulating signals) on a high frequency wave (called, the carrier wave). The resultant wave is called the modulated wave, which is transmitted.
Read the above passage and answer the following questions:
(i) What are the Audio frequency and Radio Frequency ranges?
(ii) Why audio frequency signals, as such cannot be transmitted over long distances?
(iii) What does the phenomenon imply in day to day life?
4)
Demodulation is the reverse process of modulation, which is performed in a receiver to recover the original modulating signals. At the receiving end, the signals are generally weak due to attenuation in the channel. The receiver selects only the desired signal, rejecting the unwanted (noise) signals and amplifies the same.
Read the above passage and answer the following questions:
(i) What are the main functions of a demodulator?
(ii) Give any two examples of demodulators.
(iii) What does the phenomenon of demodulation imply in day to day life?

CBSE 12th Standard Physics Subject Electromagnetic Induction Value Based Questions 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
Rita noticed that the transformer in her locality gets damaged quite often leading to long power cuts. She complained to the power distribution company with the help of her father and got the transformer replaced?
(i) What is the principle of a transformer?
(ii) Mention two losses which take place in a transformer.
(iii) Values exhibited by Rita in dealing with the above situation.
2)
Mr.Ramesh a physics teacher, was doing an experiment in lab using dry cell battery. The dry cell was weak, giving less voltage, which was not sufficient to give proper reading. One of the students asked, "Sir, can't we step-up the voltage using a transformer?" Teacher replied, "No, we cannot step up DC voltage using step up transformer and explained the reason and working of a transformer". The student then constructed a transformer for his physics project and studied the factors responsible for losses in a transformer.
1. What values are displayed by the student?
2. Why can transformer not be used to step-up DC voltage?
3)
Rahul after having lived in US for 12 years returned back to India. He had a discussion with his cousin Sumit on domestic power supply in US and in India.In US domestic power supply is at 110V, 50Hz, whereas in India it is 220V, 50Hz.. Rahul was stressing that US supply is better than Indian supply. Both went to Sumit's father an electrical Engineer and asked his opinion on the issue. He explained that both the supplies have advantages as well as disadvantages.
1. What values are used by Rahul and Summit?
2. Write one advantage and one disadvantage of 220V supply over 110V supply.

CBSE 12th Standard Physics Subject Moving Charges And Magnetism Value Based Questions 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
While watching Discovery channel Sheela was impressed that certain organisms have the ability to sense the field lines of earth's magnetic field. They use this ability to travel from one location to another, Sheela wanted to find the angle of dip at her place. She then mounted the compass on a cardboard and placed it vertically along the magnetic meridian. She was able to measure the angle of dip
(a) What values did Sheela have?
(b) Define the magnetic element of earth.
2)
Babita and Sheela class XII students were assigned a project based on magnetism.In their project work, they calculated the value of earth's magnetic field.When they submitted their project work for verification.
Mr.Raj, their physics teacher, corrected the mistake.Hew also suggested few books which could be of use to them.
What values did Mr.Raj exhibit towards his students? Mention any two.
3)
A Ramesh while doing his physics practical in a class, found that if a voltmeter, an ammeter and a resistance are connected in series to a lead accumulator, there is deflection in the voltmeter but the deflection in ammeter is negligible. He discussed his problem with all his class fellows but no one could explain the reason. Harshpreet was also studying in his class. When he discussed the problem with her, she explained the reason and then whole class was informed by both of them.
(a) What was the reason for deflection in voltmeter and negligible deflection in the ammeter?
(b) What value were displayed by Ramesh and Harshpreet?

CBSE 12th Standard Physics Subject Value Based Questions 5 Mark Questions 2021 Part - I - by Sharma - Kochi - May 31, 2021 - View & Read

1)
Shikhaj was working on a project for science exhibition. He considered a capacitance of 2\(\mu F\) having a capacity of operating under 1kV potential. When he reached to shop, he found that the shopkeeper is having a capacitors of 1 \(\mu F\) of 400 V rating. Shikhaj calculated minimum number of capacitances of 1 \(\mu F\) each, so he could arrange to form a capacitor of 2 \(\mu F\) .
Answer the following questions based on the above information:
(i) What are the calculations done by Shikhaj?
(ii) What do you think of Shikhaj?
2)
Ramaniamma was a childless window. She ran her life only by the pension for the Sr. citizens from the Government. When she switches ON one bulb in her house, all the other appliances get switched OFF. She could not even spend for an electrician. Sujatha living nearby decided to do something for her. She referred to Physics books and learned that the series combination for the household connection could be the reason. She called an electrician and had the circuit changed to parallel combination. The problem was solved and Ramaniamma was happy. She thanked Sujatha for her help to solve the problem.
Read the above passage and answer the following questions.
(i) What are the values possessed by Sujatha?
(ii) Why a parallel combination is used for household? Give two advantages.
3)
When a galvanometer of resistance G is shunted with a low resistance S, then the effective resistance \({ Re }_{ ff }\)of galvanometer becomes
\( { Re }_{ ff }=\frac { GS }{ G+S } \)
If the current is passed through such a galvanometer, then the major amount of current flows through the shunt and the rest through the galvanometer, then the major amount of current flows through the shunt and the rest through galvanometer., the current divides itself in the inverse ratio of resistances.
Read the above passage and answer the following questions:
(i) Why is the resistance of shunted galvanometer lower than that of a shunt?
(ii) A galvanometer of resistance.\(30\Omega \) What the fraction of the main current passes (i) through the galvanometer and (ii) through the galvanometer and (ii) through the shunt?
(iii) What are the basic values you learn from the above study?
4)
Aarushi wanted to perform an experiment of Faraday's law of electromagnetic induction. She told her father to bring some of the instruments such as a torch bulb, a coil and a bar magnet. She connected the bulb with the two terminals of the coil. And to check for induced emf, she moved the bar magnet back and forth near to the coil. The bulb started to glow. All her mother, father and elder brother surprised of this activity.
(i) What are the values displayed by Aarushi?
(ii) Give the Faraday's law of electromagnetic induction?
(iii) Write the equation to calculate induced emf of a coil of N number of turns?
5)
The number of electrical generators used in areas where small workshops exist created a lot of pollution. Kamal and his five friends did a survey and realised that like a multistoried building, a common generator could be set up for all these small workshops so that the noise and air pollution could be reduced. They had a tough time convincing the local bodies and now they are going to the NGO's and some financiers to help them to set up the generators.
Read the above passage and answer the following questions:
(i) What values did Kamal and his friends show>
(ii) Kamal peddles a stationary bicycle, the pedals of the bicycle are attached to a 100 turn coil of area 0.1m². The coil rotates at half a revolution per second and it is placed in a uniform magnetic field of 0.01 T perpendicular to the axis of rotation of the coil. What is the maximum voltage generated in the coil?

CBSE 12th Standard Physics Subject Value Based Questions 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 31, 2021 - View & Read

1)
A Ramesh while doing his physics practical in a class, found that if a voltmeter, an ammeter and a resistance are connected in series to a lead accumulator, there is deflection in the voltmeter but the deflection in ammeter is negligible. He discussed his problem with all his class fellows but no one could explain the reason. Harshpreet was also studying in his class. When he discussed the problem with her, she explained the reason and then whole class was informed by both of them.
(a) What was the reason for deflection in voltmeter and negligible deflection in the ammeter?
(b) What value were displayed by Ramesh and Harshpreet?
2)
Rahul after having lived in US for 12 years returned back to India. He had a discussion with his cousin Sumit on domestic power supply in US and in India.In US domestic power supply is at 110V, 50Hz, whereas in India it is 220V, 50Hz.. Rahul was stressing that US supply is better than Indian supply. Both went to Sumit's father an electrical Engineer and asked his opinion on the issue. He explained that both the supplies have advantages as well as disadvantages.
1. What values are used by Rahul and Summit?
2. Write one advantage and one disadvantage of 220V supply over 110V supply.
3)
Two boys, on their way from school were discussing seriously about something. They both were blowing soap bubbles and were thrilled to watch the expanding bubble with spectacular colour rings. Rita, a class XII student, was watching them for a long time, walking behind them. Suddenly she realised that the kids did not look at the traffic in that junction area. She rushed to them and instructed them to be cautious while on the road. She also explained the importance of traffic rules and told them that obeying traffic rules not only makes us safe but also others safe.
(i) What are the values highlighted by Rita
(ii) why are colours formed on bubbles?
4)
Modulation is the phenomenon of superimposing the low audio frequency base band message or information signals (called the modulating signals) on a high frequency wave (called, the carrier wave). The resultant wave is called the modulated wave, which is transmitted.
Read the above passage and answer the following questions:
(i) What are the Audio frequency and Radio Frequency ranges?
(ii) Why audio frequency signals, as such cannot be transmitted over long distances?
(iii) What does the phenomenon imply in day to day life?
5)
Demodulation is the reverse process of modulation, which is performed in a receiver to recover the original modulating signals. At the receiving end, the signals are generally weak due to attenuation in the channel. The receiver selects only the desired signal, rejecting the unwanted (noise) signals and amplifies the same.
Read the above passage and answer the following questions:
(i) What are the main functions of a demodulator?
(ii) Give any two examples of demodulators.
(iii) What does the phenomenon of demodulation imply in day to day life?

CBSE 12th Standard Physics Subject Value Based Questions 3 Mark Questions 2021 Part - II - by Sharma - Kochi - May 31, 2021 - View & Read

1)
Babita and Sheela class XII students were assigned a project based on magnetism.In their project work, they calculated the value of earth's magnetic field.When they submitted their project work for verification.
Mr.Raj, their physics teacher, corrected the mistake.Hew also suggested few books which could be of use to them.
What values did Mr.Raj exhibit towards his students? Mention any two.
2)
Mr.Ramesh a physics teacher, was doing an experiment in lab using dry cell battery. The dry cell was weak, giving less voltage, which was not sufficient to give proper reading. One of the students asked, "Sir, can't we step-up the voltage using a transformer?" Teacher replied, "No, we cannot step up DC voltage using step up transformer and explained the reason and working of a transformer". The student then constructed a transformer for his physics project and studied the factors responsible for losses in a transformer.
1. What values are displayed by the student?
2. Why can transformer not be used to step-up DC voltage?
3)
Ravi is using yellow light in a single slit diffraction experiment with slit width of 0.6mm. The teacher has replaces yellow light by x-rays. Now he is not able to observe the diffraction pattern. He feels sad. Again he teacher replaces x-rays by yellow light and the diffraction pattern appears again. The teacher now explains the facts about the diffraction and
Which value is displayed by the teacher.
Give the necessary condition for the diffraction.
4)
Arun lives in Delhi, His grandfather lives in a small village in Haryana.He always misses his grandfather, so he decided to purchase a mobile phone for his grandfather.He saved his pocket money and purchased the mobile phone.Now his grandfather communicates often with his family and now they are happy.
(a) What are the values Arun displayed in his act?
(b) Name the type of wave used in mobile communication.Write its frequency range.
5)
Rita was studying in 10th class, one day she asked her father to explain the working of remote control of TV. Her father was not knowing the answer, but he made up his mind to understand the working of remote control. He found one shop where remote controls were repaired. The shopkeeper showed to Rita's father the inside of the remote control and explained her the working. Rita's father explained her the working of remote control, Rita was happy and satisfied.
(a) What are the values Rita's father displayed in his act?
(b) Name the diode used in remote control.

CBSE 12th Standard Physics Subject Value Based Questions 3 Mark Questions 2021 Part - I - by Sharma - Kochi - May 31, 2021 - View & Read

1)
While watching Discovery channel Sheela was impressed that certain organisms have the ability to sense the field lines of earth's magnetic field. They use this ability to travel from one location to another, Sheela wanted to find the angle of dip at her place. She then mounted the compass on a cardboard and placed it vertically along the magnetic meridian. She was able to measure the angle of dip
(a) What values did Sheela have?
(b) Define the magnetic element of earth.
2)
Rita noticed that the transformer in her locality gets damaged quite often leading to long power cuts. She complained to the power distribution company with the help of her father and got the transformer replaced?
(i) What is the principle of a transformer?
(ii) Mention two losses which take place in a transformer.
(iii) Values exhibited by Rita in dealing with the above situation.
3)
Sumeet a 5^th class student observed a coloured film of oil on water when illuminated by white light. He felt happy and surprised to see this. His teacher explained him the reason behind it. The child then gives an example of spreading of kerosene oil on water to prevent malaria and dengue.
(i) What value was displayed by his teacher?
(ii) Name the phenomenon involved.
4)
Physics teacher in the semiconductor chapter explained that a very low voltage is required for the operation of semiconductor diodes, but Ramesh found that at home the supply used for charging mobile or CD player etc. is 220V. He was confused. Then, he discussed this problem with his classmates and with the teacher. The teacher explained the reason and Mohan was satisfied.
(a) Why is 220V ac supply used in charger and CD player?
(b) What values were displayed by Mohan?
5)
Demodulation is the reverse process of modulation, which is performed in a receiver to recover the original modulating signals. At the receiving end, the signals are generally weak due to attenuation in the channel. The receiver selects only the desired signal, rejecting the unwanted (noise) signals and amplifies the same.
Read the above passage and answer the following questions:
(i) What are the main functions of a demodulator?
(ii) Give any two examples of demodulators.
(iii) What does the phenomenon of demodulation imply in day to day life?

CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits HOT Questions 5 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Write the truth table for a NAND gate connected as given in the figure. Hence, identity the exact logic operation carried out by this circuit.

CBSE 12th Standard Physics Subject Wave Optics HOT Questions 5 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
The critical angle between a given transparent medium and air is denoted by C. A ray of light in air enters this transparent medium at an angle of incidence equal to polarizing angle p. Deduce a relation for the angle of refraction in terms of C.
2)
Suppose while sitting in a parked car, you notice a jogger approaching towards you in the rear view mirror having R = 2m. If the Jogger is running at a speed of 5m/s, how fast is the image of Jogger moving. When the Jogger is (i) 39m (ii) 29m (iii) 19 m and (iv) 9 m away?
3)
A teacher has given three lenses of power 0.5D, 4D and 10D to a studet. He is not sure as to which lens should he use for constructing a good astronomical telescope. So, he consults his seniors and the teacher, and then constructs a telescope. Later, he shows this telescope to the junior classes and ex[plains about the choice of lenses.
Read the above passage and give the answer of the following questions:
(i) What values has he shown by doing these?
(ii) Which lenses are used as objective and which one as eyepiece?
4)
(i) Obtain the conditions for the bright and dark fringes in diffraction pattern due to a single narrow slit illuminated by a monochromatic source. Explain clearly, why the secondary maxima go on becoming weaker with increasing of their order?
(ii) When the width of the slit is made double, how would this affect the size and intensity of the central diffraction band? Justify your answer.
5)
(i) In a double slit experiment using light of wavelength 600 nm, the angular width of the fringe formed on a distant screen is \(0.1^o\) . Find the spacing between the two slits.
(ii) Light of wavelength 5000\(\dot { A } \) propagating in air gets partly reflected from the surface of water. How will the wavelengths and frequencies of the reflected and refracted light be affected?

CBSE 12th Standard Physics Subject Moving Charges And Magnetism HOT Questions 3 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
A short bar magnet placed with its axis at \(30°\)to a uniform magnetic field of 0.2T experiences a torque of 0.06Nm.
(i) Calculate magnetic moment of the magnet and
(ii) Find out what orientation of the magnet corresponds to a stable equilibrium in the magnetic field.
2)
An iron sample having mass 8.4 kg is repeatedly taken over cycles of magnetisation and demagnetization at a frequency of 50Hz.It is found that energy of 3.2 J is dissipated as heat in the sample in 30 minutes. If the density of iron is \(7200kg{ m }^{ -3 }\) calculate the value of energy dissipated per unit volume per cycle in the iron sample.
3)
To increase the current sensitivity of a moving coil galvanometer by 50%, its resistance is increased so that the new resistance becomes twice its initial resistance. By what factor does its voltage sensitivity change?
4)
A galvanometer having 30 divisions has a current sensitivity of \(20\mu \)A per division. It has a resistance of \(25\Omega \). How will you convert it into an ammeter measuring upto I A? How will you convert in this ammeter into a voltmeter reading upto 1 V?
5)
Relative permeability of a material, \(\mu\)_r= 0.5. Identify the nature of the magnetic material and write its relation to magnetic susceptibility.

CBSE 12th Standard Physics Subject Alternating Current HOT Questions 3 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
A 12 V resistance and an inductance of \(\frac { 0.05 }{ \pi } H\) are connected in series.Across the end of this ciuit an alternating voltage of 130 V and frequency 50 Hz is connected. Calculate the current in the circuit and the potential difference across the inductance.
2)
In a series L-C-R circuit connected to an AC source of variable frequency and voltage \(V\ =\ { V }_{ m }\ sin\ \omega t\), draw a plot showing the variation of current I with angular frequency \(\omega \), for two different values of resistance R₁and R₂(R₁>R₂). Write the condition under which the phenomenon of resistance occurs. For which value of the resistance out of the two curves, a sharper resonance is produced? Define Q-factor of the circuit and give its significance.
3)
An AC voltage \(V={ V }_{ m }sin \ \omega t\) is applied across an inducer of inductance L.Find the instantaneous power P_i supplied to the inductor. Show graphically the variation of P_iwith \(\omega t\) .
4)
(i) Determine the value of phase difference between the current and the voltage in the given series L-C-R circuit.

(ii) Calculate the Value of additional capacitor which may be joined suitably to the capacitor C that would make the power factor of the circuit unity.
5)
Study the circuits (a) and (b) shown in the figure answer the following question:

(i) Under which conditions would the rms currents in the two circuits be the same?
(ii) Can the rms current in circuit (b) be larger than that in (a)?

CBSE 12th Standard Physics Subject Communication Systems HOT Questions 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Figure shows a communication system. Which is the output power when input signal is 1.01 mW? (Gain in dB=\(10\log { _{ 10 }\frac { { P }_{ 0 } }{ { P }_{ 1 } } } \))
2)
Consider an optical communication system operating at = 800nm. Suppose only 1% of optical source frequency is the available channel bandwidth for optical communication. How many channels can be accommodated for transmitting
(i) audio signals requiring a bandwidth of 8kHz?
(ii) video TV signals requiring an approximate bandwidth of 4.5MHz? Support your answer with suitable calculations.
3)
An audio signal is modulated by a carrier wave of 20 MHz such that the bandwidth required for modulation is 3kHz.Could this wave be demodulated by a diode detector which has the values of R and C as
(i) R=\(1k\Omega ,C=0.01\mu F\)
(ii) R=\(10k\Omega ,C=0.01\mu F\)
(iii) R=\(10k\Omega ,C=1\mu F\)
4)
Distinguish between 'sky waves' and 'space waves' modes of propagation in communication system.
(a) Why is sky wave mode propagation restricted to frequencies upto 40 MHz?
(b) Give two examples where space wave mode of propagation is used.
5)
Describe briefly, by drawing suitable diagrams, the (i) sky wave and (ii) space wave modes of propagation. Mention the frequency range of the waves in these modes of propagation.

CBSE 12th Standard Physics Subject Communication Systems HOT Questions 3 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
The maximum peak-to-peak voltage of an AM wave is 16 mV and the minimum peak-to-peak voltage is 4 mV.Calculate the modulation index.
2)
For an optical communication system, operating at \(\lambda =800\ nm\), only 1% of the optical source frequency is the available channel bandwidth. How many channels can be accomdated for transmitting video T.V. signal requiring an approximate bandwidth of 4.5 MHz?
3)
A ground receiver station is receiving a signal at 8 MHz, transmitted from a ground transmitter at a height of 289 m located at a distance of 100 km. Identify whether it is coming via space wave or sky wave propagation or satellite transponder. Radius of earth = 6.4 x 10⁶ m. Maximum number density of electrons in ionosphere = 10¹² m^-3.
4)
If sky wave with a frequency of 60 MHz is incident on D-region at an angle of 30°, then find the angle of refraction.
5)
What is meant by selectivity and sensitivity of radio receiver?

CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits HOT Questions 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits HOT Questions 3 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
The input resistance of a silicon transistor is \(665\Omega \). Its base current is changed by \(15\ \mu A\) which results in the change in collector current by 2 mA. This transistor is used as a common emitter amplifier with a load resistance of \(5 \ k\Omega \). Calculate
(a) current gain, \(\beta _{ ac }\) ;
(b) transconductance \(g_{ m }\) and
(c) voltage gain \(A_{ v }\) of the amplifier.
2)
As, we know, an n-type semiconductor has large number of electrons but it is still electrically neutral. Why?
3)
How would you set up a circuit to obtain NOT gate using a transistor?
4)
A circuit symbol of a logic gate and two input wave forms A and B are shown.
a) Name the logic gate

b) Give the output wave form
5)
The diode shown in the figure has a constant voltage drop of 0.5V at all currents and a maximum power rating of 100mW. What should be the value of resistance R connected in series, for maximum current.?

CBSE 12th Standard Physics Subject Nuclei HOT Questions 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
The isotopes of \({ U }^{ 238 }\ and\ { U }^{ 235 }\) occur in nature in the ratio 140 : 1. Assuming that at the time of earth's formation, they were present in equal ratio, make an estimate of the age of the earth. The half lives of \({ U }^{ 238 }\ and\ { U }^{ 235 }\) are \(4.5\times { 10 }^{ 9 }\) years and \(7.13\times { 10 }^{ 8 }\) years respectively.
Given : \(\log _{ 10 }{ 140 } =2.1461,\log _{ 10 }{ 2 } =0.3010\)
2)
Two radioactive nuclei A and B, in a given sample disintegrates into a stable nucleus C. At time t = 0, number of A species are 4N₀ and that of B are N₀. Half-life of A (for conversion to C) is 1 min whereas, that of B is 2 min. Initially, there are no nuclei of C present in the sample. When number of nuclei of A and B are equal, then what would be the number of nuclei of C present in the sample?
3)
(a) Deduce the expression ,N = \({ N }_{ 0 }{ e }^{ -\lambda t }\), for the law of radioactive decay
(b) (i) Write symbolically the process expressing the \({ \beta }^{ + }\) decay of \(_{ 11 }^{ 22 }{ Na }\) . Also write the basic nuclear process underlying this decay.
(ii) Is the nucleus formed in the decay of the nucleus \(_{ 11 }^{ 22 }{ Na }\), an isotope or an isobar?
4)
Write symbolically the process expressing the \({ \beta }^{ + }\) decay of \(_{ 11 }^{ 22 }{ Na }\). Also write the basic nuclear process underlying this decay.
5)
Is the nucleus formed in the decay of the nucleus \(_{ 11 }^{ 22 }{ Na }\), an isotope or an isobar?

CBSE 12th Standard Physics Subject Nuclei HOT Questions 3 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
(a) If \(\alpha \)-decay of \(_{ 92 }{ { U }^{ 238 } }\) is energetically allowed (i.e. the decay products have a total mass less than the mass of \(_{ 92 }{ { U }^{ 238 } }\)), what prevents \(_{ 92 }{ { U }^{ 238 } }\) from decaying all at once? Why is its half life so large?
(b) The \(\alpha \)-particle faces a Coulomb barrier. A neutron being uncharged faces no such barrier. Why does the nucleus \(_{ 92 }{ { U }^{ 238 } }\) not decay spontaneously, by emitting a neutron?
2)
The half-lives of radioactive nuclides that emit \(\alpha \)-rays vary from microsecond to billion years. What is the reason for this large variation in the half life of alpha emitters?
3)
There is a stream of neutrons with a kinetic energy of 0.0327 eV. If the half life of neutrons is 700 seconds, what fraction of neutrons will decay before they travel a distance of 10 m? Given mass of neutron \(=1.675\times { 10 }^{ -27 }kg.\)
4)
The radioactive decay rate of a radio active element is found to be \({ 10 }^{ 3 }\) disintegrations/sec. at a certain time. If half life of the element is one second, what would be the decay rate after 1 sec. and after 3 sec.?
5)
The isotopes of \({ U }^{ 238 }\ and\ { U }^{ 235 }\) occur in nature in the ratio 140 : 1. Assuming that at the time of earth's formation, they were present in equal ratio, make an estimate of the age of the earth. The half lives of \({ U }^{ 238 }\ and\ { U }^{ 235 }\) are \(4.5\times { 10 }^{ 9 }\) years and \(7.13\times { 10 }^{ 8 }\) years respectively.
Given : \(\log _{ 10 }{ 140 } =2.1461,\log _{ 10 }{ 2 } =0.3010\)

CBSE 12th Standard Physics Subject Atoms HOT Questions 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
A point source of \(\gamma \)-radiation has a half life of 30 minutes. The initial count rate, recorded by Geiger counter placed 2 m from the source is \(360{ s }^{ -1 }.\) The distance between the counter and the source is altered. After 1.5 hours, the count rate recorded in \(5{ s }^{ -1 }.\) What is the new distance between the counter and the source?
2)
Consider a radioactive nucleus A which decays to a stable nucleus C through the following sequence:
A \(\longrightarrow \) B \(\longrightarrow \) C
where, B is an intermediate nuclei, which is also radioactive. Considering that there are N₀ atoms of A initially, plot the graph showing the variation of number of atoms of A and B versus time.
3)
At atomic power nuclear reactor can deliver 300 MW. The energy released due to fission of each nucleus of uranium atoms U²³⁸ is 170 MeV. What will be the number of atoms fissioned per hour?
4)
(i) Using Bohr's second postulate of quantisation of orbital angular momentum, show that the circumference of the electron in the nth orbital state in H-atom is n times the de-Broglie wavelength associated with it.
(ii) The electron in H-atom is initially in the third excited state. What is the maximum number of spectral lines which can be emitted when it finally moves to the ground state?
5)
Nuclei with magic number of protons Z = 2,8,20,28,50,52 and magic number of neutrons N = 2,8,20,28,5082 and 126 are found to be very stable.
(i) Verify this by calculating the proton separation energy \({ S }_{ p }\) for \({ 120 }_{ Sn }(Z=50)\) and \({ 121 }_{ Sn }(Z=51)\) .The proton separation energy for a nuclide is the minimum energy required to separate the least tightly bound proton from a nucleus of that nuclide.It is given by
\({ S }_{ P }=({ M }_{ Z-1,N }+{ M }_{ H }-{ M }_{ Z,N }){ c }^{ 2 }\)
\(given,{ 119 }_{ In }=118.9058 \ u,\)
\( { 120 }_{ Sn }=119.902199 \ u,\)
\({ 121 }_{ Sb }=120.903824 \ u,\)
\( { 1 }_{ H }=1.0078252u\)
(ii) What does the existence of magic number indicate?

CBSE 12th Standard Physics Subject Atoms HOT Questions 3 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Show that the instantaneous rate of change of activity of a radioactive substance is inversely proportional to the square of its half life.
2)
A positronium atom is a bound state of an electron \(\left( { e }^{ - } \right) \) and its antiparticle, the positron \(\left( { e }^{ + } \right) \) revolving round their centre of mass. In which part of the em spectrum does the system radiate when it de-excites from its first excited state to the ground state?
3)
A population inversion for two energy levels is often described by assigning a negative Kelvin temperature to the system. What negative temperature would describe a system in which population of the upper energy level exceeds that of the lower by 10% and the energy difference between the two levels is 2.2 eV?
4)
A radioactive sample decays with an average life of 20 milli sec. A capacitor of capacitance \(100\mu F\) is charged to some potential and then the plates are connected through a resistance R. What should be the value of R so that the ratio of the charge on the capacitor to the activity of the radioactive sample remains constant in time?
5)
A point source of \(\gamma \)-radiation has a half life of 30 minutes. The initial count rate, recorded by Geiger counter placed 2 m from the source is \(360{ s }^{ -1 }.\) The distance between the counter and the source is altered. After 1.5 hours, the count rate recorded in \(5{ s }^{ -1 }.\) What is the new distance between the counter and the source?

CBSE 12th Standard Physics Subject Dual Nature of Radiation and Matter HOT Questions 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Find the de Broglie wavelength associated with an electron moving with velocity 0.6c. Given, rest mass of electron = \(9.1\times { 10 }^{ -31 }kg\) ,\(h=6.63\times { 10 }^{ -34 }Js\)
2)
An electron, \(\alpha \) -particle and a proton have the same de-Broglie wavelengths. Which of
theseparticle has
(i) minimum kinetic energy?
(ii) maximum kinetic energy and why?
In what way has the wave nature of electron beam exploited in an electron microscope?
3)
A student performs an experiment on photoelectric effect, using two materials A and B. A plot of V_stop versus v is given in the figure.
(i) Which material A or B has a higher work function?

(ii) Given the electric charge of an electron =\(1.6\times { 10 }^{ -19 }C\), find the value of h obtained from the experiment for both A and B.
Comment on whether it is consistent with thr Einstein's theory.
4)
Plot a graph showing the variation of stopping potential with the frequency of incident radiation for two different photosensitive materials having work functions W₀₁ and W₀₂ (W₀₁> W₀₂). On what' factors does the
(i) slope and
(ii) intercept of the lines depend ?
5)
Draw a plot showing the variation of potoelectric current with collector plate potential for two different frequencies, v₁ > v₂ of incident radiation having the same intensity. In which case will the stopping potential be hgiher ? Justify your answer.

CBSE 12th Standard Physics Subject Dual Nature of Radiation and Matter HOT Questions 3 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Find the de Broglie wavelength associated with an electron moving with velocity 0.6c. Given, rest mass of electron = \(9.1\times { 10 }^{ -31 }kg\) ,\(h=6.63\times { 10 }^{ -34 }Js\)
2)
An electron, \(\alpha \) -particle and a proton have the same de-Broglie wavelengths. Which of
theseparticle has
(i) minimum kinetic energy?
(ii) maximum kinetic energy and why?
In what way has the wave nature of electron beam exploited in an electron microscope?
3)
A student performs an experiment on photoelectric effect, using two materials A and B. A plot of V_stop versus v is given in the figure.
(i) Which material A or B has a higher work function?

(ii) Given the electric charge of an electron =\(1.6\times { 10 }^{ -19 }C\), find the value of h obtained from the experiment for both A and B.
Comment on whether it is consistent with thr Einstein's theory.
4)
Plot a graph showing the variation of stopping potential with the frequency of incident radiation for two different photosensitive materials having work functions W₀₁ and W₀₂ (W₀₁> W₀₂). On what' factors does the
(i) slope and
(ii) intercept of the lines depend ?
5)
Draw a plot showing the variation of potoelectric current with collector plate potential for two different frequencies, v₁ > v₂ of incident radiation having the same intensity. In which case will the stopping potential be hgiher ? Justify your answer.

CBSE 12th Standard Physics Subject Wave Optics HOT Questions 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
A jar of height is filled with a transparent liquid of refractive index \(\mu \)(figure). At the centre of the jar on the bottom surface is a dot. Find the minimum diameter of a disc, such that when placed on the top surface symmetrically about the centre, the dot is invisible.

The problem is based on the principle of total inter reflection and area of visibility.
2)
Show that for a material with refractive index \(\mu \ge \sqrt { 2 } \), light incident at any angle shall be guided along a length perpendicular to the incident face.
3)
(i) Light passes through two polaroids \({ P }_{ 1 }and{ P }_{ 2 }\) with pass axis of \({ P }_{ 2 }\) with pass axis of \({ P }_{ 2 }\) making in angle \(\theta \) with the pass axis of \({ P }_{ 1 }\) . For what value of \(\theta \) is the intensity of emergent light zero?
(ii) A third polaroid is placed between \({ P }_{ 1 }and{ P }_{ 2 }\) with its pass axis making an angle \(\beta \) with the pass axis is \({ P }_{ 1 }\) . Find the value of \(\beta \) for which the intensity of light from \({ P }_{ 2 }\) is \(\frac { { I }_{ 0 } }{ 8 } \) , where \({ I }_{ 0 }\) is the intensity of light on the polaroid \({ P }_{ 1 }\) .
4)
Explain with the help of ray diagram, the working of an astronomical telescope. The magnifying power of a telescope in its normal adjustment is 20. If the length of the telescope is 105 cm in this adjustment, find the focal length of the two lenses.
5)
In an experiment with two coherent sources, the amplitude of the intensity variation is found to be 5% of the average intensity. What will be the relative intensities of the light waves of interfering source.

CBSE 12th Standard Physics Subject Wave Optics HOT Questions 3 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
A convex lens of focal length 30 cm is placed coaxially with a convex mirror of radius of curvature 20 cm. The two are kept at 15 cm from each other. A point object lies 60 cm in front of the convex lens. Draw a ray diagram to show the formulation of the image by the combination. Determine the nature and position of the image formed.
2)
Three light rays, red(R), green(G) and blue (B) are incident on a right angled prism ABC at face AB. The refractive indices of the material of the priam for red, green and blue wavelengths are 1.39, 1.44 and 1.47, respectively.Out of the three, which colour of ray will emerge out of face AC? Justify your answer.Trace the path of these rays after passing through face AB.
3)
A jar of height is filled with a transparent liquid of refractive index \(\mu \)(figure). At the centre of the jar on the bottom surface is a dot. Find the minimum diameter of a disc, such that when placed on the top surface symmetrically about the centre, the dot is invisible.

The problem is based on the principle of total inter reflection and area of visibility.
4)
Show that for a material with refractive index \(\mu \ge \sqrt { 2 } \), light incident at any angle shall be guided along a length perpendicular to the incident face.
5)
(i) Light passes through two polaroids \({ P }_{ 1 }and{ P }_{ 2 }\) with pass axis of \({ P }_{ 2 }\) with pass axis of \({ P }_{ 2 }\) making in angle \(\theta \) with the pass axis of \({ P }_{ 1 }\) . For what value of \(\theta \) is the intensity of emergent light zero?
(ii) A third polaroid is placed between \({ P }_{ 1 }and{ P }_{ 2 }\) with its pass axis making an angle \(\beta \) with the pass axis is \({ P }_{ 1 }\) . Find the value of \(\beta \) for which the intensity of light from \({ P }_{ 2 }\) is \(\frac { { I }_{ 0 } }{ 8 } \) , where \({ I }_{ 0 }\) is the intensity of light on the polaroid \({ P }_{ 1 }\) .

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance HOT Questions 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Three capacitors of 1\(\mu F\), 2\(\mu F\) and 3\(\mu F\) are joined in series.
(i) How many times will the capacity become when they are joined in parallel?
(ii) Determine the charge supplied by the battery of 100 V to the maximum resultant capacitor among both the arrangement.
2)
Two charges +Q and -Q are kept at points (-x₂, 0) and (x₁, 0) respectively, in the XY-plane. Find the magnitude and direction of the net electric field at the origin (0, 0).
3)
An electricdipole consists of two opposite charges each of magnitude 1.0\(\times\)10^-6C separated by 2cm. The dipole is placed in an external uniform field of 1\(\times\)10⁵ N/C. Find
(i) the maximum torque exterted by the field on the dipole
(ii) the work which an external agent will have to do in turning the dipole through 180⁰ starting the position, \(\theta\) = 0⁰.
4)
A charge Q is distributed over two concentric hollow shaperes of radii r and R( > r) such that their surface densities are equal. Find the potential at the common centre.
5)
(i) How is the electric field due to a charged parallel plate capacitor affected, when a dielectric slab is inserted between the plates fully occupying the intervening region?
(ii) A slab of material of dielectric constant K has the same area as the plates of a parallel plate capacitor but has thickness \(\frac{1}{2}\) d, where d is the separation between the plates. Find the expression for the capacitance when the slab is inserted between the plates.

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance HOT Questions 3 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
On what range of separation between the charges, the coulomb's force law is found valid?
2)
A charge is situated outside an uncharged hollow conductor experiences a force if another charge B is placed inside the conductor, but B does not experience any force. Why? Does it not violate the third law of motion ?
3)
Can two balls having same kind of charge on them attract each other? Explain.
4)
An infinite number of charges each equal to q, are placed along X-axis at x = 1, x = 2, x = 4, x = 8, ............... and so on.
(i) Find the electric field at a point x = 0 due to this set up of charges.
(ii) What will be the electric field if in the above set up the consecutive charges have opposite signs.
5)
An uncharged capacitor is connected to a battery. Show that half the energy supplied by the battery is lost as heat while charging the capacitor.

CBSE 12th Standard Physics Subject Communication Systems HOT Questions 2 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
In the given block diagram of a receiver identify the boxes labelled as X and Y and write their functions.
2)
(a) Describe briefly the three factors which justify the need for translating a low frequency signal into high frequencies before transmission.
(b) Figure shows a block diagram of a detector for AM signal.

Draw the waveforms for the
(i) input AM wave at A,
(ii) output B at the rectifier, and (iii) output signal at C.
3)
Differentiate between (i) PAM and (ii) PPM
4)
An AM wave is represented by the expression: v = 5 (1 + 0.6 cos 6280 t) sin 221 x 104 t volts
(i) What are the maximum and minimum amplitudes of the AM wave.
(ii) What frequency components are contained in the modulated wave
5)
The antenna current of an AM transmitter is 8A when only carrier is sent but it increases to 8.93A when the carrier is sinusoidally modulated. Find the percent-age modulation index

CBSE 12th Standard Physics Subject Dual Nature of Radiation and Matter HOT Questions 2 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
A proton and an \(\alpha \)particle are accelerated through the same potential. Which one of the two has
(i) greater value of de-Broglie wavelength associated with it and
(ii) less kinetic energy?
give reasons to justify your answer
2)
Find the ratio of the de-Broglie wavelength associated with protons accelerated through a potential of 128 V and a particles accelerated through a potential of 64 V.
To calculate the ratio of de-Baroglie wavelength of two particle find the ratio in terms of symbols and then put the given numerical values.
3)
What is the
(i) momentum
(ii) speed
(iii) de-Broglie wavelength of an electron with kinetic energy of 120 eV?
4)
X-rays fall on a photosensitive surface to cause photoelectric emission. Assuming that the work function of the surface can be neglected, find the relation between the de-Broglie wavelength (\(\lambda \)) of the electrons emitted to the energy (E_v) of the incident photons. Draw the nature of the graph for Aas a function of E_v.

CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits HOT Questions 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
what is knee voltage in a junction Diode?
2)
In transistor a current controlled (or)temperature controlled device?.
3)
In a given diagram ,is the diode reverse (or) forward biased?
4)
Which gate is represented by the following diagram?
5)
The ratio of number of free electrons to holes ne/nh for two different materials A and B are 1 and <1 respectively. Name the type of semi conductor to which A and B belongs.

CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits HOT Questions 1 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
How does the energy gap of an intrinsic semiconductor vary, when doped with a trivalent impurity?
2)
Why are photodiodes used preferably in reverse bias condition?
3)
What is the condition for the state of saturation of a transistor?
4)
The graph shown in the figure represents a plot of current versus voltage for a given semiconductor. Identify the region, if any, over which the semiconductor has a negative resistance.
5)
A 200 V AC supply is connected between points A and B as shown in the figure. What will be the potential difference V across the capacitor?

CBSE 12th Standard Physics Subject Nuclei HOT Questions 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
which have greater ionizing power:α-particles or \(\beta\)-particles?
2)
Why neutrons are considered as ideal particle for nuclear reactions?
3)
Does the ratio of neutrons and protons in the nucleus increase, decreases or remain the same after the emission of \(\alpha\) – particles?
4)
A radio isotope of silver has a half life of 20 minutes. What fraction of the original mass would remain after one hour?
5)
What changes takes place in the nucleus when a \(\gamma\) – rays is emitted?

CBSE 12th Standard Physics Subject Nuclei HOT Questions 1 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Compare the radii of two nuclei with mass numbers 1 and 27 respectively.
2)
In a particular fission reaction, a \(_{ 92 }{ { U }^{ 235 } }\) nucleus captures a slow neutron. The fission products are three neutrons, a \(_{ 57 }{ La^{ 142 } }\)nucleus and a fission product \(_{ Z }{ { X }^{ A } }\). What is the value of Z?
3)
In a typical nuclear reaction e.g
\(_{ 1 }^{ 2 }{ H+_{ 1 }^{ 2 }H{ \longrightarrow _{ 2 }^{ 3 }{ He } }+n+3.27MeV }\)
although number of nucleons is conserved,yet energy is released.How?Explain.
4)
What characteristic property of nuclear force explain the constancy of binding energy per nucleon (BE/A) in the range of mass number 'A' lying 30
5)
Two nuclei have mass numbers in the ratio 1:8.What is the ratio of their nuclear radii?

CBSE 12th Standard Physics Subject Atoms HOT Questions 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
The half life of a radioactive substance in 30 days. What is the time taken for ¾ of its original mass to disintegrate?
2)
Why is the ionization power of \(\alpha\) – particle of greater than \(\gamma\) – rays?
3)
(b) Which one of the two is likely to be more stable? Give reason.
4)
A certain radio active substance has a half life of 30 days. What is the disintegration constant? Find its average life
5)
Neon -23 decays in the following way
²³Ne₁₀---------------\(\rightarrow\)²³Na₁₁ + ⁰e_-1+y
Find the minimum and maximum kinetic energy that the \(\beta\)-particle can have. The atomic masses of ²³Ne₁₀ and ²³Na₁₁ are 22.99454 and 22.98984 respectively.

CBSE 12th Standard Physics Subject Atoms HOT Questions 1 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Imagine removing one election from He⁴ and He³.Their energy levels, as worked out on the basis of Bohr's model will be very close. Explain why?
2)
When white light is passed through an unexcited gas, what happens to the transmitted light?
3)
Why the simple Bohr's model cannot be directly applied to calculate the energy levels of an atom with many electrons?
4)
Why is it found experimentally difficult to detect neutrions in nuclear \(\beta -\)decay?
5)
what conclusions were drawn from the observation in which few alpha-particle were seen rebounding from gold foil?

CBSE 12th Standard Physics Subject Dual Nature of Radiation and Matter HOT Questions 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
The de-broglie wave length of a photon is same as the wave length of electron. Show that K.E. of a photon is 2mc \(\lambda \)/h times K.E. of electron. Where ‘m’ is mass of electron,c is velocity of light.
2)
Following table gives values of work function for a few photosensitive metal

S.NO Metal Work functions

1 Na 1.92

2 K 2.15

3 Mo 4.17

If each metal is exposed to radiation of wavelength 300nm which of them will not emit photo electron
3)
The De-broglie wave length associated with proton and neutron are equal.Which has greater kinetic energy?
4)
If the potential difference used to accelerate electron is doubled , by what factor the Debroglie wave length of the electron beam changed
5)
Visible light can not eject photo electrons from copper surface, whose work function is 4.4 ev , why? Prove mathematically

S.NO	Metal	Work functions
1	Na	1.92
2	K	2.15
3	Mo	4.17

CBSE 12th Standard Physics Subject Dual Nature of Radiation and Matter HOT Questions 1 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
The stopping potential in an experiment on a photoelectric effect is 1.5V. What is the maximum kinetic energy of the photoelectrons emitted?
2)
A photon and an electron have been same de-Broglie wavelength which one has higher total energy?
3)
Show graphically how the stopping potential for a given photosensitive surface varies with the frequency of incident radiations.
4)
If wavelength of electromagnetic waves are doubled what will happen to energy of photon?
5)
Alkali metals are most suitable for photoelectric emission. Why?

CBSE 12th Standard Physics Subject Wave Optics HOT Questions 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Will the focal length of a lens for red light be more same or less than that for blue light?
2)
An unsymmetrical double convex thin lens forms the image of a point on its axis will the position of the image change is the lens are reversed?
3)
In a moving car, radio signals are interrupted sometimes. Why?
4)
If the source of light used in Young's double slit experiment is changed from red to violet, what will happen to the fringe?
5)
Why is the diffreaction of sound waves more evident in daily expreience than that of light wave?

CBSE 12th Standard Physics Subject Wave Optics HOT Questions 1 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
What happens to the intensity of light diverging from a point source?
2)
Two plane mirrors are inclined at an angle \(\theta \). It is found that a ray incident on one mirror at any angle rendered parallel to itself after reflection from both the mirrors. What will be the value of \(\theta \)?
3)
Given the effect on image, if lower half of the concave mirror is blackened.
4)
A convex lens is placed in contact with a planne mirror. A point object at a distance of 20 cm and image conciding with itself. What is the focal length of the lens?
5)
Will the focal length of a lens for red light be more same or less than that for blue light?

CBSE 12th Standard Physics Subject Electromagnetic Waves HOT Questions 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Mention the law, that which asserts that the electric field lines cannot form close loops?
2)
The energy of the electromagnetic wave is in the order of 15KV . To which part of the spectrum does it belong?
3)
Name em waves are used in telecommunication.
4)
what is condition for obtaining displacement current between the plate of the capacitor?
5)
Mention the pair of space and time varying E and B fields which would generate a plane em wave travelling in the z-direction?

CBSE 12th Standard Physics Subject Electromagnetic Waves HOT Questions 1 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Show, by giving a simplex example, how EM waves carry energy and momentum.
2)
Why is the Quantity \({ \varepsilon }_{ 0 }d\Phi _{ E }/dt\) called the displacement current?
3)
What is the ratio of speed of infrared and ultraviolet rays in vacuum?
4)
An electromagnetic wave consists of oscillating electric and magnetic fields. What is the phase relationship between these oscillations?
5)
If the area of the TV telecast is to be doubled then what will be the height of the transmitting antenna ?

CBSE 12th Standard Physics Subject Alternating Current HOT Questions 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
A train is moving with uniform speed from North and South, why will any induced emf appear across the ends of its axle?
2)
Two coils are being moved out of magnetic field- one coil is moved rapidly and the other slowly. In which case is more work done and why?
3)
How does the self-inductance of an air-core coil change, when
(i) the number of turns in the coil is decreased,
(ii) an iron rod is introduced in the coil? A copper coil L wound on a soft iron core and a lamp B are connected to a battery E through a tapping key K when the key is suddenly opened, the lamp flashes for an instant to much greater brightness. Explain

CBSE 12th Standard Physics Subject Alternating Current HOT Questions 1 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Consider a magnet surrounded by a wire with an ON/OFF switch in the figure. If the switch is thrown from the OFF position (open circuit) to the ON position (closed circuit), will a current flow in the circuit? Explain.

The magnetic flux linked with a uniform surface area A in a uniform magnetic field is given by \(\phi \) = B.A = BA cos \(\theta \) .So flux linked will change, only when either B or A or the angle between B and A change.
2)
In the following figure, the rectangular loop of wire is being pulled to the right, away from the long straight wire through which a steady current I flows upward as shown. Does the current induced in the loop flow in the clockwise sense or in the counter-clockwise sense? Justify.
3)
The axes of two magnets are collinear. One has poles of strength 80 Am separated by 125 mm, and the second has a magnetic moment of 12 A-m² with poles of strength 160 Am. Find the attractive force between the magnets if the north pole of one is 45 mm from the south pole of the second
4)
A coil A is connected to voltmeter V and the other coil B to an alternating current source D. If a large copper sheet CC is placed between the two coils, how does the induced e.m.f in the coil A change due to current in coil B?
5)
An inductor L of reactance XL is connected in series with a bulb B to an A.C. source as shown in the figure. Briefly explain, how does the brightness of the bulb change when
(a) Number of turns of the inductor is reduced and
(b) A capacitor of reactance X_C =X_L is included in series in the same circuit.

CBSE 12th Standard Physics Subject Electromagnetic Induction HOT Questions 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
A particle with charge ‘q’ and mass ‘m’ is shot with kinetic energy K into the region between two plates as shown in the figure. If the magnetic field between the plates is B and as shown, how large must B be if the particle is to miss collision with the opposite plate?
2)
A bar PQ of mass M is suspended by two wires as shown below. Assume that a uniform magnetic field B is directed into the page. Find the tension in each supporting wire when the current through the bar is I.
3)
A bar of mass M is suspended by two springs as shown below. Assume that a magnetic field B is directed out of the page. Each spring has a spring constant K. Describe the bar’s displacement when a current I is sent through it in the direction shown
4)
A magnet is moved in the direction indicated by an arrow between two coils A and B as shown below. Suggest the direction of induced current in each coil L.
5)
A copper ring is held horizontally and bar magnet is dropped through the ring with its length along the axis of the ring. Will the acceleration of the falling magnet be equal to, greater than or less than that due to gravity?

CBSE 12th Standard Physics Subject Electromagnetic Induction HOT Questions 1 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
A transformer has 150 turns in its primary and 1000 in secondary. If the primary is connected to 440 V DC supply, what will be the induced voltage in the secondary side?
2)
Give the direction in which the induced current flows in the coil mounted on an insulating stand when a bar magnet is quickly moved along the axis of the coil from one side to the other as shown.
3)
A cylindrical bar magnet is kept along the axis of a circular coil, when the magnet is rotated (a) about its own axis, and (b) about an axis perpendicular to the length of the magnet, in which case the induced emf will be more?
4)
How is the mutual inductance of a pair of coils affected when separation between the coils is increased? The number of turns of each coil is increased? A thin iron sheet is placed between the two coils, other factors remaining the same? Explain your answer in each case.
5)
Define self-inductance in terms of work done against the induced emf.

CBSE 12th Standard Physics Subject Moving Charges And Magnetism HOT Questions 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Two concentric circular coils A and B of radii 10 cm and 6 cm respectively, lie in the same vertical plane containing the north to south direction. coil A has 30 turns and carries a current of 10 A. Coil B has 40 turns and carries a current of 15 A .the sense of the current in A is anticlockwise and clockwise in B for an observer looking at the coils facing west. Give the magnitude and direction of net magnetic field.
2)
The vertical component of earth’s magnetic field at a given place is \(\sqrt { 3 } \) times its horizontal component. If the total intensity of earth’s magnetic field at a place is 0.4 G , find the value of horizontal component of earths field and angle of dip.
3)
north to south direction.Specify the direction in which the uniform magnetic field should be set up to prevent the electron from deflecting from its straight line path.
4)
A straight wire of mass 200g and the length 1.5m carries a current of 2A. It is suspended in mid air by a uniform horizontal magnetic field B. What is the magnitude of B in tesla?
5)
A rigid circular loop of radius r and mass m lies in the x-y plane of a flat table and has a current I flowing in it. At this particular place the earth’s magnetic field is B = Bxi +Bzk. What is the value of I, so that loop starts tilting?

CBSE 12th Standard Physics Subject Moving Charges And Magnetism HOT Questions 1 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
A copper wire is bent into a square of each side 6cm.If a current of 2A is passed through a wire what is the magnetic field at the centre of the square?
2)
Find the magnetic moment of a wire of length l carrying current I bent in the form of a circle
3)
When current is flowing through two parallel conductors in the same direction they attract while two beams of electrons moving in the same direction repel each other. Why?
4)
Draw diagrams to show behavior of magnetic field lines near a bar of (i) Alluminium (ii) copper and (iii) mercury cooled to a very low temperature 4.2 K
5)
The hysteresis loss for a sample of 6 kg is 150 J/M² /cycle. If the density of iron is 7500 kg/m3 , calculate the energy loss per hour at 40cycle

CBSE 12th Standard Physics Subject Current Electricity HOT Questions 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
If the length of the wire conductor is doubled by stretching it, keeping potential difference constant by what factor the drift speed of the electron changed.
2)
If the temperature of the conductor increases, how does the relaxation time of electron changes
3)
A heater joined in series with the 60W bulb. With change of bulb with 100 W in the circuit, the rate heat produce by the heater will more or less or remain same
4)
What will be the change in the resistance of the circular wire, when its radius is halved and length is reduced by 1/4^th of original length.
5)
Two 120V light bulbs, one of 25W and another of 200W are connected in series. One bulb burnt out almost instantaneously? Which one was burnt and why?

CBSE 12th Standard Physics Subject Current Electricity HOT Questions 1 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
In an experiment of meter bridge, the balancing length of the wire is l. What would be its value, if the radius of the meter bridge wire is double? Justify your answer.
2)
If p.d.v applied across a conductor is increased to 2v, how will the draft velocity of the electrons change?
3)
A 10Ω thick wire is stretched so that its length becomes three times. Assuming that there is no change in its density on stretching. Calculate the resistance of new wire
4)
You are given 8 \(\Omega \) resistor. What length of wire of resistance 120 Ωm-1 should be joined in parallel with it to get a value of 6 \(\Omega \) ?
5)
Two wire of equal length one copper and manganin have same resistance , which wire is thicker?

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance HOT Questions 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Each of the uncharged capacitor in the fig.Has a capacitance of 25\(\mu \)F. what charge shall flow through the meter M when the switch S is Closed?
2)
Charge of 2C is placed at the centre of a cube volume 8 cm³. What is the electric flux passiing through one face?
3)
Find the equivalent capacitance between A & B , if Capacitance of each Capacitor is C
4)
Eight identically charged drops are joined to form bigger drop. By what factor the charge and potential change?
5)
Three charges Q, +9 and +9 are placed at the vertices of a right angle isosceles triangle as shown, Find the magnitude of Q for which net electrostatic energy of the configuration is zero.

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance HOT Questions 1 Mark Questions 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Do electrons tend to go to regions of high potential or low potential?
2)
What is the net charge on a charged capacitor?
3)
What is the solid angle subtended by a hemisphere at a point inside it?
4)
Does the charge outside the Gaussian surface contribute to total electric flux?
5)
Quarks are the building blocks of nucleons and possess fractional electronic charge. Does this discovery violate the principle of quantization of charge?

CBSE 11th Standard Physics Subject HOT Questions 5 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Mandeep's mother had put lot of clothes for washing in the washing machine, but the machine did not start and an indicator was showing that the lid of the machine did not close. Mandeep seeing his mother disturbed thought that, he would close the lid by applying some force but would close the lid by applying some force but realised that the mechanism was different. It was a magnetic system. He went to the shop and got a small magnetic door closer and put it on the lid of the machine. The machine started working. His mother was happy that Mandeep helped her to save 500 rs also.
i) What were the values developed by Mandeep?
ii) What values did his mother impart to Mandeep?
iii) Every magnetic configuration has a North pole and a South pole, What about the field due to toroid?
2)
A magnetic dipole is placed in a uniform magnetic field with its axis tilted with respect to its position of stable equilibrium. Deduce an expression for the time period of (small amplitude) oscillation of this magnetic dipole about an axis, passing through its centre and perpendicular to its plane. If this bar magnet is replaced by a combination of two similar bar magnets, placed over each other, how will the time period vary?
3)
A group of students while coming from the school noticed a box marked "Danger HT 2200 V" at a substation in the main street. They did not understand the utility of a such high voltage, while they argued, the supply was only 220 V. They asked their teacher this question the next day. The teacher thought it to be an important question and therefore explained to the whole class.
Answer the following questions:
(i) What device is used to bring the high voltage down to low voltage of AC current and what is the principle of its working?
(ii) Is it possible to use this device for bringing down the high DC voltage to the low voltage? Explain.
(iii) Write the values displayed by the students and the teacher.
4)
A resistor of \(400\Omega \) an inductor of \(\frac { 5 }{ \pi H } \)and a capacitor of \(\frac { 50 }{ \pi } \mu F\) are connected in series across a source of alternating voltage of 140 \(sin\ \pi t\ V\). Find the voltage (rms) across the resistor, the inductor and the capacitor. Is the algebraic sum of these voltage more than the source voltage? If yes, resolve the paradox.
5)
The critical angle between a given transparent medium and air is denoted by C. A ray of light in air enters this transparent medium at an angle of incidence equal to polarizing angle p. Deduce a relation for the angle of refraction in terms of C.

CBSE 11th Standard Physics Subject HOT Questions 5 Mark Questions 2021 Part - II - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Suppose that the electric field amplitude of an electromagnetic wave is E₀= 120N/C and that its frequency is v = 50.0 MHz.
(a) Determine B₀, \(\omega \) , k and \(\lambda \).
(b) Find expressions for E and B.
2)
(i) Obtain the conditions for the bright and dark fringes in diffraction pattern due to a single narrow slit illuminated by a monochromatic source. Explain clearly, why the secondary maxima go on becoming weaker with increasing of their order?
(ii) When the width of the slit is made double, how would this affect the size and intensity of the central diffraction band? Justify your answer.
3)
(i) In a double slit experiment using light of wavelength 600 nm, the angular width of the fringe formed on a distant screen is \(0.1^o\) . Find the spacing between the two slits.
(ii) Light of wavelength 5000\(\dot { A } \) propagating in air gets partly reflected from the surface of water. How will the wavelengths and frequencies of the reflected and refracted light be affected?
4)
Ajeet's younger brother was just seeing class 12th books. He wondered to know the structure of atoms and arrangement of electrons and protons in them. As he was a class 6th student, he did not understand the whole concept of atomic structure. Ajeet helped him to understand the structure of atoms.
Read the above passage and answer the following questions:
(i) What are the values shown by Ajeet?
(ii) On which metal Rutherford performed \(\alpha \) - particles scattering experiment?
(iii) How Rutherford concluded that at the centre of atom there is massive nucleus which contains positive charge?
5)
Write the truth table for a NAND gate connected as given in the figure. Hence, identity the exact logic operation carried out by this circuit.

CBSE 11th Standard Physics Subject HOT Questions 5 Mark Questions 2021 Part - I - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Mandeep's mother had put lot of clothes for washing in the washing machine, but the machine did not start and an indicator was showing that the lid of the machine did not close. Mandeep seeing his mother disturbed thought that, he would close the lid by applying some force but would close the lid by applying some force but realised that the mechanism was different. It was a magnetic system. He went to the shop and got a small magnetic door closer and put it on the lid of the machine. The machine started working. His mother was happy that Mandeep helped her to save 500 rs also.
i) What were the values developed by Mandeep?
ii) What values did his mother impart to Mandeep?
iii) Every magnetic configuration has a North pole and a South pole, What about the field due to toroid?
2)
Two concentric circular coils x and y of radii 16 cm and 10 cm respectively lie in the same vertical plane containing the North to South direction. Coil x has 20 turns and carries a current of 16 A, coil y has 25 turns and carries a current of 18 A. The sense of the current in x is anti-clockwise and clockwise in y, for an observer looking at the coils facing West. Find the magnitude and direcion of the net magnetic field due to the coils at their centre.
Here, we have to find the magnetic field due to two coils. So, first of all find the magnetic fields due to individual coil and find the net field using the law of vector addition, as magnetic field is a vector quantitiy.
3)
A group of students while coming from the school noticed a box marked "Danger HT 2200 V" at a substation in the main street. They did not understand the utility of a such high voltage, while they argued, the supply was only 220 V. They asked their teacher this question the next day. The teacher thought it to be an important question and therefore explained to the whole class.
Answer the following questions:
(i) What device is used to bring the high voltage down to low voltage of AC current and what is the principle of its working?
(ii) Is it possible to use this device for bringing down the high DC voltage to the low voltage? Explain.
(iii) Write the values displayed by the students and the teacher.
4)
Suppose that the electric field amplitude of an electromagnetic wave is E₀= 120N/C and that its frequency is v = 50.0 MHz.
(a) Determine B₀, \(\omega \) , k and \(\lambda \).
(b) Find expressions for E and B.
5)
Suppose while sitting in a parked car, you notice a jogger approaching towards you in the rear view mirror having R = 2m. If the Jogger is running at a speed of 5m/s, how fast is the image of Jogger moving. When the Jogger is (i) 39m (ii) 29m (iii) 19 m and (iv) 9 m away?

CBSE 12th Standard Physics Subject HOT Questions 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
An infinite number of charges each equal to q, are placed along X-axis at x = 1, x = 2, x = 4, x = 8, ............... and so on.
(i) Find the electric field at a point x = 0 due to this set up of charges.
(ii) What will be the electric field if in the above set up the consecutive charges have opposite signs.
2)
Show that the force on each plate of a parallel plate capacitor has a magnitude equal to1/2 QE. where Q is the charge on the capacitor and E is the magnitude of electric field between the plates. Explain the origin of the factor 1/2.
Here, we can use the content that the work done in displacing the plates against the force is equal to the increase in energy of the capacitor.
3)
(i) How is the electric field due to a charged parallel plate capacitor affected, when a dielectric slab is inserted between the plates fully occupying the intervening region?
(ii) A slab of material of dielectric constant K has the same area as the plates of a parallel plate capacitor but has thickness \(\frac{1}{2}\) d, where d is the separation between the plates. Find the expression for the capacitance when the slab is inserted between the plates.
4)
An iron sample having mass 8.4 kg is repeatedly taken over cycles of magnetisation and demagnetization at a frequency of 50Hz.It is found that energy of 3.2 J is dissipated as heat in the sample in 30 minutes. If the density of iron is \(7200kg{ m }^{ -3 }\) calculate the value of energy dissipated per unit volume per cycle in the iron sample.
5)
A 12 V resistance and an inductance of \(\frac { 0.05 }{ \pi } H\) are connected in series.Across the end of this ciuit an alternating voltage of 130 V and frequency 50 Hz is connected. Calculate the current in the circuit and the potential difference across the inductance.

CBSE 12th Standard Physics Subject HOT Questions 3 Mark Questions 2021 Part - II - by Sharma - Kochi - May 27, 2021 - View & Read

1)
A charge is situated outside an uncharged hollow conductor experiences a force if another charge B is placed inside the conductor, but B does not experience any force. Why? Does it not violate the third law of motion ?
2)
Two charges +Q and -Q are kept at points (-x₂, 0) and (x₁, 0) respectively, in the XY-plane. Find the magnitude and direction of the net electric field at the origin (0, 0).
3)
In a potentiometer arrangement, a cell of emf 2.25 V gives a balance point at 30 cm length of the wire.If the cell is replaced by another cell and the balance point shifts to 60 cm, what is the emf of the second cell?
4)
A circular coil of 20 turns and radius 10 cm is placed in a uniform magnetic field of 0.10 T normal to the plane of the coil. If the current in the coil is 5.0 A, what is the
(a) total torque on the coil,
(b) total force on the coil,
(c) average force on each electron in the coil due to the magnetic field?
(The coil is made of copper wire of cross-sectional area 10^-5 m², and the free electron density in copper is given to be about 10²⁹ m^-3)
5)
An iron sample having mass 8.4 kg is repeatedly taken over cycles of magnetisation and demagnetization at a frequency of 50Hz.It is found that energy of 3.2 J is dissipated as heat in the sample in 30 minutes. If the density of iron is \(7200kg{ m }^{ -3 }\) calculate the value of energy dissipated per unit volume per cycle in the iron sample.

CBSE 12th Standard Physics Subject HOT Questions 3 Mark Questions 2021 Part - I - by Sharma - Kochi - May 27, 2021 - View & Read

1)
An infinite number of charges each equal to q, are placed along X-axis at x = 1, x = 2, x = 4, x = 8, ............... and so on.
(i) Find the electric field at a point x = 0 due to this set up of charges.
(ii) What will be the electric field if in the above set up the consecutive charges have opposite signs.
2)
Show that the force on each plate of a parallel plate capacitor has a magnitude equal to1/2 QE. where Q is the charge on the capacitor and E is the magnitude of electric field between the plates. Explain the origin of the factor 1/2.
Here, we can use the content that the work done in displacing the plates against the force is equal to the increase in energy of the capacitor.
3)
(i) How is the electric field due to a charged parallel plate capacitor affected, when a dielectric slab is inserted between the plates fully occupying the intervening region?
(ii) A slab of material of dielectric constant K has the same area as the plates of a parallel plate capacitor but has thickness \(\frac{1}{2}\) d, where d is the separation between the plates. Find the expression for the capacitance when the slab is inserted between the plates.
4)
A long horizontal rigidly supported wire carries \({ i }_{ a }\)of 100 A. Directed above it and parallels to it is a fine wire that carries a current \({ i }_{ a }\)of 20A and weighs 0.073N/m. How far above the lower wire should the second wire be kept if we wish to support it by magnetic repulsion?
Given permeability constant \({ \mu }_{ 0 }=4\pi \times { 10 }^{ -7 } \ Wb\ { A }^{ -1 }{ m }^{ -1 }\)
5)
When a capacitor is connected in series LR circuit the alternating current flowing in the circuit increases. Explain why.

CBSE 12th Standard Physics Subject HOT Questions 2 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
A and B have identical size and same mass. A becomes A²⁺ and B become B^2- . Will A²⁺ and B^2- still have the same mass? Why?
2)
A charged Particle q is shot towards another charged particle Q which is fixed , with a speed v. It approaches Q up to a closet distance r and then returns, If q were given a speed 2 v the n find the closet distance of approach.
3)
Use Kirchhoff's rules to determine the potential difference between the points A and D. When no current flows in the arm BE of the electric network shown in the figure below.
4)
A magnetic needle free to rotate in a vertical plane parallel to the magnetic meridian has its North tip down at 60⁰ with the horizontal. The horizontal component of the earth's magnetic field at the place is known to be 0.4 gauss. Determine the magnitude of the earth's magnetic field at the place.
5)
You are given a copper wire carrying current I of length L. Now the wire is turned into circular coil. Find the number of turns in the coil so that the torque at the centre of the coil is to maximum

CBSE 12th Standard Physics Subject HOT Questions 2 Mark Questions 2021 Part - II - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Guess a possible reason, why water has a much greater dielectric constant (= 80) than mica (= 6)?
2)
A thin fixed ring of radius 2 m has a positive charge of 10^-6C uniformly distributed over it. A particle of mass 0.9 g and having a negative charge 10^-7C is placed on the axis at a distance of 2cm from the center of the ring. Show that motion of the negatively charged particle is approximately SHM. Calculate the time period of oscillation.
3)
Three resistance 3Ω, 6Ω and 9Ω are connected to a battery. In which of them will the power dissipation be maximum if
a) They are all connected in parallel
b) They are all connected in series Give reason.
4)
You are given a copper wire carrying current I of length L. Now the wire is turned into circular coil. Find the number of turns in the coil so that the torque at the centre of the coil is to maximum
5)
Can we increase the range of a telescope by increasing the diameter of the objective lens?

CBSE 12th Standard Physics Subject HOT Questions 2 Mark Questions 2021 Part - I - by Sharma - Kochi - May 27, 2021 - View & Read

1)
A charged Particle is free to move in an electric field. Will it always move along an electric line of force ?
2)
A charged Particle q is shot towards another charged particle Q which is fixed , with a speed v. It approaches Q up to a closet distance r and then returns, If q were given a speed 2 v the n find the closet distance of approach.
3)
Three resistance 3Ω, 6Ω and 9Ω are connected to a battery. In which of them will the power dissipation be maximum if
a) They are all connected in parallel
b) They are all connected in series Give reason.
4)
Equal currents I = 2A are flowing through the infinitely long wires parallel to Y-axis located at x = +1m, x = +2m, x = +4m and so on, but in opposite directions as shown in figure. Find the magnetic field at the origin O.
5)
An electromagnet has stored 648 J of magnetic energy, when a current of 9 A exists in its coils. What average e.m.f. is induced if the current is reduced to zero in 0.45 s?

CBSE 12th Standard Physics Subject HOT Questions 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 27, 2021 - View & Read

1)
What is the solid angle subtended by a hemisphere at a point inside it?
2)
Two charges of -9C and +9C are palced at the points P(1, 0, 4) and Q(2,-1, 5) located in an electric field E = 0.20i V/cm. Calculate the torque acting on the dipole.
3)
A positively charged particle is released from rest in a uniform electric field.What happens to its electrostatic potential energy?
4)
Device an arrangemnet of three point charges separated by finite distances that has zero electric potential energy.
5)
Two wire of equal length one copper and manganin have same resistance , which wire is thicker?

CBSE 12th Standard Physics Subject HOT Questions 1 Mark Questions 2021 Part - II - by Sharma - Kochi - May 27, 2021 - View & Read

1)
In a fair weather condition,there is an electric field at the surface of the earth, pointing down into the ground. What is the electric charge on the ground in this situation?
2)
Two wire of equal length one copper and manganin have same resistance , which wire is thicker?
3)
A Current ‘I’ flows along the length of an infinitely long straight thin walled pipe. What is the magnetic field at any point on the axis of pipe?
4)
A bar magnet M is dropped so that it falls vertically through the coil C. The graph obtained for voltage produced across the coil vs time is shown in figure (b).
(i) Explain the shape of the graph.
(ii) Why is the negative peak longer than the positive peak?
5)
The figure shows an inductor L and a resistance R connected in parallel to a battery through a switch. The resistance R Which of the bulbs lights up earlier, when K is closed? Will the bulbs be equally bright after the same time?

CBSE 12th Standard Physics Subject HOT Questions 1 Mark Questions 2021 Part - I - by Sharma - Kochi - May 27, 2021 - View & Read

1)
Do electrons tend to go to regions of high potential or low potential?
2)
Two charges of -9C and +9C are palced at the points P(1, 0, 4) and Q(2,-1, 5) located in an electric field E = 0.20i V/cm. Calculate the torque acting on the dipole.
3)
Charge of 2C is placed at the centre of a cube volume 8 cm³. What is the electric flux passiing through one face?
4)
You are given 8 \(\Omega \) resistor. What length of wire of resistance 120 Ωm-1 should be joined in parallel with it to get a value of 6 \(\Omega \) ?
5)
What will be the direction of magnetic field at point O

CBSE 12th Standard Physics Subject Moving Charges And Magnetism 5 Mark Ncert Exemplar Questions 2021 - by Sharma - Kochi - May 24, 2021 - View & Read

1)
Explain using a labelled diagram, the principle and working of a moving coil galvanometer. What is the function of
(i) uniform radial magnetic field
(ii) soft iron core?
Also, define the terms
(iii) current sensitivity and
(iv) voltage sensitivity of a galvanometer.
Why does increasing the current sensitivity not necessarily increase voltage sensitivity?
2)
Ms. Kanchan, a student of PG course in nanotechnology lab in IIT Kanpur on her first day in the lab met Mr. Cobra, the lab assistant
He advised her not to touch the wires, which were suspended from the roof at every part of the lab as they were from high voltage lines.
He also told her not to bring any of the two wires closer to each other during any experimental applications. Read the above passage and answer the following questions:
(i) What values did Mr. Cobra exhibit? Give two reasons.
(ii) Why should not the the two high voltage wires be brought close to each other?
3)
In the birthday party of Kamal, his parents gave big slinkies to all his friends as a return gift. The very next day, during the physics class Mr. Mohan, the teacher explained them about the production of magnetic field using current carrying coil and also said that they can make permanent magnet, using such coils by passing high currents through them. That night Priyanshu, a friend of Kamal, asked his father about the coils, and their shape. His father asked him to bring the slinky, that his friend gave and explained the use of toroid and solenoid.
Read the above passage and answer the following questions:
(i) What value did Priyanshu's father have?
(ii) What is the difference between solenoid and toroid?
(iii) Give the value or magnitude of magnetic field in solenoid.
4)
Niyaz was using galvanometer in the practical class. Unfortunately, it fell from his hand and broke. He was upset, some of his friends advised him not to tell the teacher but Niyaz decided to tell his teacher. Teacher listened to him patiently and on knowing that the act was not intentional, but just an accident, did not scold him and used the opportunity to show the internal structure of galvanometer.
(i) What are the values displayed by Niyaz?
(ii) Give the principle of moving coil galvanometer.
(iii) How can you increase the sensitivity of a galvanometer?
5)
(i) Derive the expression for the torque on a rectangular current carrying loop suspended in a uniform magnetic field
(ii) A proton and a deuteron having equal momentum enter in a region of a uniform magnetic field at right angle to the direction of the field.Depict their trajectories in the field

CBSE 12th Standard Physics Subject Communication Systems 3 Mark Ncert Exemplar Questions With Solution 2021 - by Sharma - Kochi - May 24, 2021 - View & Read

1)
Figure shows a communication system. Which is the output power when input signal is 1.01 mW? (Gain in dB=\(10\log { _{ 10 }\frac { { P }_{ 0 } }{ { P }_{ 1 } } } \))
2)
Consider an optical communication system operating at = 800nm. Suppose only 1% of optical source frequency is the available channel bandwidth for optical communication. How many channels can be accommodated for transmitting
(i) audio signals requiring a bandwidth of 8kHz?
(ii) video TV signals requiring an approximate bandwidth of 4.5MHz? Support your answer with suitable calculations.
3)
An audio signal is modulated by a carrier wave of 20 MHz such that the bandwidth required for modulation is 3kHz.Could this wave be demodulated by a diode detector which has the values of R and C as
(i) R=\(1k\Omega ,C=0.01\mu F\)
(ii) R=\(10k\Omega ,C=0.01\mu F\)
(iii) R=\(10k\Omega ,C=1\mu F\)
4)
(i) Draw the plot of amplitude versus for an amplitude modulated wave whose carrier wave(\({ \omega }_{ c }\) ) is carrying two modulating signals, \({ \omega }_{ 1 }\) and\({ \omega }_{ 2 }\)
(ii) Is the plot symmetrical about \({ \omega }_{ c }\)?Comment especially about plot in region \(\omega <\omega _{ c }\)
(iii) Extrapolate and predict the problems, one can expect if more waves are to be modulated
(iv) Suggest solution to the above problem. In the process can one understand another advantage of modulation in terms of bandwidth?
5)
An amplitude modulated wave is as shown in the figure.Calculate
(i) the percentage modulation
(ii) peak carrier voltage and
(iii) peak value of information voltage.

CBSE 12th Standard Physics Subject Communication Systems 3 Mark Ncert Exemplar Questions 2021 - by Sharma - Kochi - May 24, 2021 - View & Read

1)
Give reason of the following:
(i) For ground wave transmission, size of antenna \(\iota \) should be comparable to wavelength \(\lambda \) of the signal, i.e. \(l=\frac { \lambda }{ 4 } \).
(ii) Audio signals, converted into an electromagnetic wave, are not directly transmitted.
(iii)The amplitude of a modulating signal is kept less than the amplitude of a carrier wave.
2)
A 50 MHz sky wave takes 4.04 ms to reach a receiver via retransmission from a satellite 600 km above the earth's surface. Assuming retransmission time by satellite negligible, find the distance between source and receiver.If communication between the two was to be done by Line of Sight(LOS) method, what should size and placement of receiving and transmitting antennas be?
3)
If the whole earth is to be connected by LOS communication using space waves (no restriction of antenna size or tower height), what is the minimum number of antenna requires? Calculate the tower height of these antennae in terms of the earth's
4)
What is space wave propagation? Give two examples of communication system which uses the space wave mode.A TV tower is 80 m tall.Calculate the maximum distance upto which the signals transmitted from the tower can be received.
5)
Figure shows a communication system. Which is the output power when input signal is 1.01 mW? (Gain in dB=\(10\log { _{ 10 }\frac { { P }_{ 0 } }{ { P }_{ 1 } } } \))

CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits 3 Mark Ncert Exemplar Questions 2021 - by Sharma - Kochi - May 24, 2021 - View & Read

1)
You are given a circuit below. Write its truth table, identify the logic operation carried out by this circuit. Draw the logic symbol of the gate it corresponds.
2)
In the circuit shown in figure, when the input voltage of the base resistance is 10 V, V_BE is zero and V_CE is also zero. Find the values of I_B, I_C and \(\beta\)
3)
Predict the effect on the electrical properties of a silicon crystal at room temperature, if every millionth silicon atom temperature, if every millionth silicon atom is replaced by an atom of indium. Given, Concentration of silicon atoms = \(5\times { 10 }^{ 28 }{ m }^{ -3 }\) intrinsic carrier concentration = \(1.5\times { 10 }^{ 16 }{ m }^{ -3 }\) H_e = 0.135 m³/ V-s and H_h = 0.048 m³/ V-s.
4)
If each diode in figure has a forward bias resistance of \(25\Omega \) and infinite resistance in reverse bias, what will be the values of the currents \(I_{ 1 },I_{ 2 },I_{ 3 } \ and \ I_{ 4 }\) ?
5)
Assuming the ideal diode, draw the output waveform for the circuit given in the figure, explain the waveform.

CBSE 12th Standard Physics Subject Nuclei 3 Mark Ncert Exemplar Questions 2021 - by Sharma - Kochi - May 24, 2021 - View & Read

1)
In a nucleus of ₉₂U²³⁸ , find the number of protons and the number of neutrons.
2)
Obtian the approximate velue of the radius of a nucleus ₉₂U²³⁸ , R₀ is 1.2 x 10^-15 m.
3)
The number of \(\alpha \)-particles scattered at an angle of 90⁰ is 100 per minute. What will be the number of \(\alpha \)-particles, when it is scattered at an angle of 60⁰?
4)
Two radioactive nuclei A and B, in a given sample disintegrates into a stable nucleus C. At time t = 0, number of A species are 4N₀ and that of B are N₀. Half-life of A (for conversion to C) is 1 min whereas, that of B is 2 min. Initially, there are no nuclei of C present in the sample. When number of nuclei of A and B are equal, then what would be the number of nuclei of C present in the sample?
5)
₈₆R²²² is converted into ₈₄Po²¹⁸. Name the particle emitted in this case and write down the corresponding equation.

CBSE 12th Standard Physics Subject Atoms 3 Mark Ncert Exemplar Questions 2021 - by Sharma - Kochi - May 24, 2021 - View & Read

1)
assume that there is no repulsive force between the electrons in an atom but the force between positive and negative charges is given by Coulomb's law as usual.Under such circumstances, calculate the ground state energy of a He-atom.
2)
(i) The radius of the innermost electron orbit of a hydrogen atom is \({ r }_{ 1 }=5.3\times 10^{ -11 }\) Calculate its radius in n=2 orbit.
(ii) The total energy of an electron in the second excited state of the hydrogen atom is -1.51eV. Find out its
(a) kinetic energy and
(b) potential energy in this state
3)
Consider a radioactive nucleus A which decays to a stable nucleus C through the following sequence:
A \(\longrightarrow \) B \(\longrightarrow \) C
where, B is an intermediate nuclei, which is also radioactive. Considering that there are N₀ atoms of A initially, plot the graph showing the variation of number of atoms of A and B versus time.
4)
A 12.5eV electron beam is used to bombard f = gaseous hydrogen at room temperature. Upto which energy level the H-atoms would be excited? Calculate the wavelengths of the first member of Lyman and first member of Balmer series.
5)
The deuteron id bound by nuclear forces just as H-atom is made up of p and e bound by electrostatic forces. If we consider the force between neutron and proton in deuteron as given in the form a coulomb potential but with an effective charge' F=\(\frac { 1 }{ { 4\pi \varepsilon }_{ 0 } } .\frac { { e }^{ '2 } }{ r } .\) Estimate the value of (e^' /e) given that the binding energy of a deuteron is 2.2MeV.

CBSE 12th Standard Physics Subject Dual Nature of Radiation and Matter Ncert Exemplar 3 Mark Questions 2021 - by Sharma - Kochi - May 24, 2021 - View & Read

1)
If h is Planck's constant, find the momentum of a wavelength 0.4\(\mathring { A } \)
2)
An electron, \(\alpha \) -particle and a proton have the same de-Broglie wavelengths. Which of
theseparticle has
(i) minimum kinetic energy?
(ii) maximum kinetic energy and why?
In what way has the wave nature of electron beam exploited in an electron microscope?
3)
(i) Write the important properties of photons which are used to establish Einstein's photoelectric equation.
(ii) Use this equation to explain the concept of
(a) threshold frequency and
(b) stopping potential.
4)
A student performs an experiment on photoelectric effect, using two materials A and B. A plot of V_stop versus v is given in the figure.
(i) Which material A or B has a higher work function?

(ii) Given the electric charge of an electron =\(1.6\times { 10 }^{ -19 }C\), find the value of h obtained from the experiment for both A and B.
Comment on whether it is consistent with thr Einstein's theory.
5)
A proton and an electron have same de-Broglie Wavelength. Which of them moves fast and which possesses more kinetic energy? Justify your answer.

CBSE 12th Standard Physics Subject Wave Optics Ncert Exemplar 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 24, 2021 - View & Read

1)
A person with a normal near point (25 cm) using a compound microscope with objective of focal length 8.0 mm and an eyepiece of focal length 2.5 cm can bring an object placed at 9.0 mm from the objective in sharp focus.What is the separation between the two lenses?Calculate the magnifying power of the microscope.
2)
The intensity at the central maxima (O) in a Young's double experiment is \(I^o\). If the distance OP equals one-third of fringe width of the pattern, show that the intensity at point P would be I₀ / 4
3)
A container is filled with water (\(\mu \) = 1.33) upto a height of 33.25 cm. A concave mirror is placed 15 cm above the water level and the image of an object placed at the bottom is formed 25 cm below the water level. What will be the focal length?
4)
Can reflection result in a plane polarised light, if the light is incident on the interface from the side with higher refractive index?
5)
In an experiment with two coherent sources, the amplitude of the intensity variation is found to be 5% of the average intensity. What will be the relative intensities of the light waves of interfering source.

CBSE 12th Standard Physics Subject Wave Optics Ncert Exemplar 3 Mark Questions 2021 - by Sharma - Kochi - May 24, 2021 - View & Read

1)
A candle flame is held 3 cm away from a concave mirror of radius of curvature 24 cm. Where is the image formed? What is the nature of the image?
2)
An object is placed in front of a convex mirror of focal length 30cm. If the image is a quarter of the size of the object, find the position of the image.
3)
The radii of curvature of the surface of a double convex lens are 20 cm and 40 cm focus length 20 cm. What is refractive index of the material of the lens?
4)
(i) A mobile phone lies along the principal axis of a concave mirror. Show with the help of a suitable diagram the formation of its image.Explain why magnification is not uniform.
(ii) Suppose the lower half of the concave mirror's reflecting surface is covered with an opaque material. What effect this will have on the image of the object? Explain.
5)
Use the mirror equation to show that,
(ii) a convex mirror always produces a virtual image independent of the location of the object.
(iii) an object placed between the pole and focus of a concave mirror produces a virtual and enlarged image.

CBSE 12th Standard Physics Subject Alternating Current Ncert Exemplar 3 Mark Questions 2021 - by Sharma - Kochi - May 24, 2021 - View & Read

1)
A magnetic field of flux density 10 T acts normally to the coil 50 turns having 100 cm² area.Find emf induced if the coil is removed from the magnetic field in 0.15 s.
2)
Calculate the value of capacity in picofarad, which will make 101.4\(\mu H\) inductance to oscillate with the frequency of 1MHz.
3)
A \(2㎌\) capacitor, \(100 \ \Omega \) resistor and 8 H inductor are connected in series with an AC source. What should be the frequency of source for which the current drawn in the circuit is maximum?
If peak value of emf of source is 200 V, find the maximum current, inductive reactance, capacitive reactance, total impedance, peak value of current in the circuit.
4)
In the L-C-R circuit, shown in the figure, the AC driving voltage is V = V_m sin \(\omega\)t.
(i) Write down the equation of motion for q(t) .
(ii) At t = t₀, the voltage source stops and R is short circuited. Now, write down how much energy is stored in each of L and C.
(iii) Describe subsequent motion of charges.
5)
1 MW power is to be delivered from a power station to a town 10 km away. One uses a pair of Cu wires of radius 0.5 cm for this purpose. Calculate the fraction of ohmic losses to power transmitted, if
(i) power is ttansmitted at 220 V. Comment on the feasibility of doing this.
(ii) a step-up transformer is used to boost the. voltage at 11000 V, power transmitted, then a step-up transformer is used to bring voltage is 220 V.(Take, P_Cu = 1.7 x 10^-8 SI unit)

CBSE 12th Standard Physics Subject Moving Charges And Magnetism Ncert Exemplar 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 24, 2021 - View & Read

1)
A uniform conducting wire of length 12 a and resistance R is wound up as a current carrying coil in the shape of
(i) an equilateral triangle of side a,
(ii) a square of sides a and
(iii) a regular hexagon of side a. The coil is connected to a voltage source V_0.Find the magnetic moment of the coils in each case.
The different shapes form figures of different area and hence, their magnetic moments vary.
2)
The vertical component of the earth's magnetic field at a place is \(0.24\sqrt { 3 } \times { 10 }^{ -4 }T\) . Find out the value of horizontal component of the earth's magnetic field, if angle of dip at that place is \({ 30 }^{ \circ }\) .
3)
A solenoid of 600 turns per meter is carrying a current of 4A. Its core is made of iron with relative permeability of 5000. Calculate the magnitudes of magnetic intensity, intensity of magnetisation and magnetifield inside the core.
4)
Answer the following questions:
i) Explain qualitatively on the basis of domain picture the irreversibility in the magnetisation curve of a ferromagnet
ii) The hysteresis loop of a soft iron piece has a much smaller area than that of a carbon steel piece. If the material is to go through repeated cycles of magnetisation, which piece will dissipate greater heat energy?
iii) A system displaying a hysteresis loop such as a ferromagnet, is a device device for storing memory. Explain the meaning of this statement.
iv) What kind of ferromagnetic material is used for coating magnetic tapes in a cassette player or for building 'memory stores' in a modern computer?
v) A certain region of space is to be shislded from magnetic fields, Suggest a method.
5)
A bar magnet of magnetic moment m and moment of inertia I (about a center, perpendicular to the length) is cut into two equal pieces, perpendicular to the length. Let T be the period of oscillations of the original magnet about an axis through the midpoint, perpendicular to the length, in a magnetic field B, what would be the similar period T^' for each piece?

CBSE 12th Standard Physics Subject Moving Charges And Magnetism Ncert Exemplar 3 Mark Questions 2021 - by Sharma - Kochi - May 24, 2021 - View & Read

1)
A current 10 A is flowing East to West in a long wire kept horizontally in the East-West direction. Find the magnitude and direction of magnetic field in a horizontal plane at a distance of 10 cm North.
2)
A cyclotron oscillator frequency is 10 MHz. What should be the operating magnetic field for accelerating \(\alpha \) -particle? If the radius of the dees is 50 cm, what is the kinetic energy in MeV of the \(\alpha \)-particle beam produced by the accelerator?
3)
Two identical magnets with a length 100cm are arranged freely with their like like poles facing in a vertical glass tube.The upper magnet hangs in air above the lower one so that the distance between the nearest poles of the magnet is 3mm. If the pole strength of the pole of these magnets is 6.64 A-m, then determine the force between the two magnets.
4)
Determine the magnitude of the equatorial fields due to a bar magnet of length 6 cm at a distance of 60 cm from its mid-point. The magnetic moment of the bar magnet is 0.60A-m²
5)
A Straight solenoid of length 50 cm has 1000 turns per metre and a mean cross-sectional area of 2 x 10-4 m². It is placed with its axis at 300, with a uniform magnetic field of 0.32 T. Find the torque acting on the solenoid when a current of 2 A is passed through it.

CBSE 12th Standard Physics Subject Communication Systems Ncert Exemplar 1 Mark Questions With Solutions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Which of the following would produce analog signals and which would produce digital signals?
(i) A vibrating tuning fork
(ii) Musical sound due to a vibrating sitar string
(iii) Light pulse
(iv) Output of NAND gate
2)
Would sky waves be suitable for transmission of TV signals of 60 MHz frequency?
3)
Two waves A and B of frequencies 2 MHz to 3 MHz, respectively are beamed in the same direction for communication via sky wave. Which one of these is likely to travel longer distance in the ionosphere before suffering total internal reflection?
4)
Compute the LC product of a tuned amplifier circuit required to generate a carrier wave of 1 MHz for amplitude modulation.
5)
Why is a AM signal likely to be more noisely than a FM signal upon transmission through a channel?

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Ncert Exemplar 1 Mark Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Two charges 2 \(\mu \)C and -2\(\mu \) C are placed at points A and B, 6 cm apart. What is the direction of the electric field at every point on this surface?
2)
Two charges of + 25\(\times\)10^-9C and -25\(\times\)10^-9 C are placed 6 m apart. Find the electric field at a point 4 m from the center of the electric dipole
(i) on axial line
(ii) on equatorial line
3)
A dipole with its charges, -q and +q, located at the points(0, -b,0) and (0, +b, 0) is present in a uniform electric field E. The equipotential surfaces of this field are planes parallel to the YZ- planes
(i) What is the direction of the electric field E?
(ii) How much torque would the dipole experience in this field?
4)
Two identical plane metallic surfaces A and B are kept parallel to each other in air, separated by a distance of 1 cm, surface A is given a positive potential of 10 V and the outer surface of B is earthed.
(i) What is the magnitude and direction of the electric field between the planes A and B?
(ii) What is the work dine in moving a charge of 20\(\mu \)C from plane A to plane B?
5)
The circular arc is shown in the figure given below, has a uniform charge per unit length of 1 x 10^-8C/m. Find the potential at the centre O of the arc.

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Ncert Exemplar 2 Mark Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Faraday entered a big metallic cage supported on insulating pillars and then charged the cage by a powerful electric machine. He remains quite safe inside the cage. Do you believe on this happening?
2)
A charge q is placed at the center of the line joining two equal charges(Q). show that the system of three charges will be in equilibrium, if q \(=-\frac { Q }{ 4 } \)
3)
A 2m insulating slab with a large aluminum sheet of area 1m² on its top is fixed by a man outside his house one evening. Will he get an electric shock, if he touches the metal sheet next morning?
4)
Guess a possible reason, why water has a much greater dielectric constant (= 80) than mica (= 6)?
5)
Automobile ignition failure occurs in damp weather. Explain, why?

CBSE 12th Standard Physics Subject Moving Charges And Magnetism Ncert Exemplar 2 Mark Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Suppose we want to verify the analogy between electrostatic and magnetic by an explicit experiment. Consider the motion of
(i) electric dipole p in an electrostatic field E and
(ii) magnetic dipole M in a magnetic field B. Write down a set of conditions on E,B,p,M so that the two motions are verified to be identical.(assume idential initial conditions)
E(r) = cB(r), suppose the angle between p and E is \(\theta \) . Torque on electric dipole moment M in magnetic field E, \(\tau =pEsin\theta \)
2)
The horizontal component of the earth's magnetic field at a place is \(\sqrt { 3 } \) times its vertical component here. Find the value of the angle of dip at that place. What is the ratio of the horizontal component to the total magnetic field of the earth at that place?
3)
A short bar magnet with its North pole facing North forms a neutral point at A in the horizontal plane. If the magnet is rotated by 90⁰ in the horizontal plane, what is the net magnetic induction at P?
4)
From molecular view point, discuss the temperature dependence of susceptibility for diamagnetism, paramagnetism and ferromagnetism.
5)
Explain quantitatively the order of magnitude difference between the diamagnetic. susceptibility of (\(N_{ 2 }(\sim 5\times { 10 }^{ -9 })\)) (at STP) and \(Cu(\sim { 10 }^{ -5 })\)

CBSE 12th Standard Physics Subject Moving Charges And Magnetism Ncert Exemplar 2 Mark Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Two long wires carrying currents I₁ and I₂ are arranged as shown in the figure. One carrying current I₁ is along the X-axis. The other carrying current I₂ is along a line parallel to Y-axis, given by x = 0 and z = d. Find the force exerted at point O₂ because of the wire along the X-axis.
2)
A cyclotron when being used to accelerate positive ions? (Mass = 6.7 x 10^-27kg, charge = 3.2 x 10^-19C) has a magnetic field of ( \(\frac { \pi }{ 2 }\)) T. What must be the value of the frequency of the applied alternating electric field to be used in it?
3)
A current of 5 A is flowing from South to North in a straight wire. Find the magnetic field due to a 1cm piece of wire at a point 1m North-East from the piece of wire.
4)
A short bar magnet has a magnetic moment of 0.48 J/T. Give the direction and magnitude of the magnetic field produced by the magnet at a distance of 10cm from the centre of the magnet on
(i) the axis,
(ii) the equatorial lines (normal bisector) of the magnet.
5)
If two magnets having magnetic moments M and M\(\sqrt { 3 } \) are joined to form a cross (i.e. X). The combination is suspended freely in a uniform magnetic field. In equilibrium position, the magnet having magnetic moment M makes an angle \(\theta \) with the field. Calculate the value of \(\theta \)

CBSE 12th Standard Physics Subject Magnetism And Matter Ncert Exemplar 2 Mark Questions With Solutions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Consider the plane S formed by the dipole axis and the axis of the earth. Let P be point on the magnetic equator in S. Let Q be the point of intersection of the geographical and magnetic equators. Obtain the declination and dip angles at P and Q.
2)
From molecular view point, discuss the temperature dependence of susceptibility for diamagnetism, paramagnetism and ferromagnetism.
3)
A ball of superconducting matesial is dipped in liquid nitrogen and placed near a bar magnet.
(i) In which direction will it move?
(ii) What will be the direction of its magnetic moment?
4)
Explain quantitatively the order of magnitude difference between the diamagnetic susceptibility of \(\mathrm{N}_{2}\left(\sim 5 \times 10^{-9}\right)\) (at STP) and \(\mathrm{Cu}\left(\sim 10^{-5}\right)\)
5)
A proton has spin and magnetic moment just like an electron. Why then its effect is neglected in magnetism of materials?

CBSE 12th Standard Physics Subject Electromagnetic Induction Ncert Exemplar 2 Mark Questions With Solutions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Consider a closed loop C in a magnetic field as shown in the figure. The flux passing through the loop is defined by choosing a surface whose edge coincides with the loop and using the formula
\(\phi \) = B₁dA₁, B₂ dA₂....Now, if we choose two different surfaces S₁ and S₂ having C as their edge, would we get the same answer for flux. Justify your answer.
2)
(i) A metal ring is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring. What will be the acceleration of a falling magnet?
(ii) Consider a metal ring kept on top of a fixed solenoid (say on cardboard) (see figure). The center of the ring coincides with the axis of the solenoid. If the current is suddenly switched ON, the metal ring jumps up. Explain.
3)
Consider a magnet surrounded by a wire with an ON/OFF switch as shown in the figure. If the switch is thrown from the OFF position (open circuit) to the ON position (closed circuit), will a current flow in the circuit? Explain
4)
A solenoid is connected to a battery, so that a steady current flows through it. If an iron core is inserted into the solenoid, will the current increase or decrease? Explain
5)
Amagnetic field in a certain region is given by \(\mid \mathbf{B}=B_{0} \cos (\omega t) \hat{\mathbf{k}}\) and a coil of radius a with resistance R, is placed in the xy-plane with its centre at the origin in the magnetic field as shown in the figure. Find the magnitude and the direction of the current at (a, 0, 0) at
\(t=\frac{\pi}{2 \omega}, t=\frac{\pi}{\omega} \text { and } t=\frac{3 \pi}{2 \omega}\)

CBSE 12th Standard Physics Subject Alternating Current Ncert Exemplar 2 Mark Questions With Solutions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
A capacitor C, a variable resistance R and a bulb B are connected in series to the AC mains in circuit as shown in the figure.The bulb glows of the bulb change, if
(i) a dielectric slab is introduced between the plates of the capacitor, keeping resistance R to be same;
(ii) the resistance R is increased keeping will capacitance?
2)
Show that heat produced in a cycle of AC is same as the heat produced by DC with \(I={ I }_{ rms }\).
3)
In series L-C-R circuit, the plot of I_max\(\omega \) versus is shown in the figure. Find the bandwidth and mark in the figure.
4)
A series L-C-R circuit with \(R=20\Omega \), L = 1.5H and \(C=5\mu F\) is connected to a variable frequency of 200 V AC supply. When the frequency of the supply equals the natural frequency of the circuit, what is the average power transferred to the circuit, what is the average complete cycle?
5)
Obtain the resonant frequency \(({ \omega }_{ r })\) of a series L-C-R circuit with L = 2.0 H, \(C=32\mu F \) and \(R=10\Omega \) . What is the Q-value of this circuit?

CBSE 12th Standard Physics Subject Electromagnetic Waves Ncert Exemplar 2 Mark Questions With Solutions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
You are given a \(2\mu F\) parallel plate capacitor. How would you establish an instantaneous displacement current of 1 mA in the space between its plates?
2)
Show that the radiation pressure exerted by an EM wave of intensity I on a surface kept in vacuum is \(\frac{I}{c}\).
3)
What happens to the intensity of light from a bulb if the distance from the bulb is doubled? As a laser beam travels across the length of a room, its intensity essentially remains constant. What geometrical characteristic of LASER beam is responsible for the constant intensity which is missing in the case of light from the bulb?
4)
Even though an electric field E exerts a force qE on a charged particle yet the electric field of an electromagnetic wave does not contribute to the radiation pressure (but transfers energy). Explain.
5)
When an ideal capacitor is charged by a DC battery, no current flows. However, when an AC source is used, the current flows continously. How does one explain this, based on the concept of displacement current?

CBSE 12th Standard Physics Subject Wave Optics Ncert Exemplar 2 Mark Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
A thin convex lens of focal length 25 cm is cut into two pieces 0.5 cm above the principal axis. The top part is placed at (0, 0) and an object placed at(-50 cm, 0)Find coordinates of the image.
There is no effect on the focal length of the lens if it cut as given in the question.
2)
A convex lens of focal length f₁ is kept in contact with a concave lens of focal length f₂ find the focal length of the combination
3)
The near vision of an average person is 25 cm. To view an object with an angular magnification of 10. what should be the power of the microscope?
4)
Consider a two slit interference arrangement (shown in figure) such that the distance of the screen from the slits is half the distance between the slits. Obtain the value of D in terms of \(\lambda \) such that the first minima on the screen falls at a distance D from the centre O.

For n^th minima to be formed on the screen path difference between the rays coming from S₁and S₂ must be \(\left( 2n-1 \right) \frac { \lambda }{ 2 } .\)
5)
A polaroid I is placed in front of a monochromatic source. Another polaroid II is placed in front of this polaroid II is now placed in between I and II. In this case, will light emerge from II. Explain

CBSE 12th Standard Physics Subject Wave Optics Ncert Exemplar 2 Mark Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Is Huygen's principle valid for longitundinal sound waves?
2)
Consider a point at the focal point of covergent lens. Another covergent lens of short focal length is placed on the other side. What is the nature of the wavefronts emerging from the final image?
3)
A Cassegrain telescope uses two mirrors as shown in the figure. Such a telescope is built with the mirrors 20mm apart. If the radius of curvature of large mirror is 220mm and the small mirror is 140 mm, where will the final image of an object at infinity be?
4)
An erect image 3 times the size of the object is obtained with a concave mirror of radius of curvature 36cm. What is the position of the object?
5)
A short object of length L is placed along the principal axis of a concave mirror away from focus. The object distance is u. If the mirror has a focal length f, what will be the length of the image? You may take L <, |v - f|.
The length of image is the separation between the images formed by mirror of the extremities of object.

CBSE 12th Standard Physics Subject Dual Nature of Radiation and Matter Ncert Exemplar 2 Mark Questions With Solutions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
(i) In the explanation of photoelectric effect, we assume one photon of frequency v collides with an electron and transfer its energy.This leads to the equation for the maximum energy E_maxof the emitted electron as \({ E }_{ max }=hv-{ \phi }_{ 0 }\)
Where \({ \phi }_{ 0 }\)is the work function of metal.If an electron absorbs two photons(each of frequency v) What will be the maximum energy for the emitted electron?
(ii) Why is this fact(two-photon absorption) not taken into consideration in our discussion of the stopping potential?
2)
Consider figure for photoemission. How would you reconcile with momentum conservation? Note light (photons) have momentum in a different direction than the emitted electrons.
3)
Draw a graph to show the variation of stopping potential with frequency of radiation incident on a metal plate. How can the value of Planck's constant be determined from this graph?
4)
Find the ratio of the de-Broglie wavelength associated with protons accelerated through a potential of 128 V and a particles accelerated through a potential of 64 V.
To calculate the ratio of de-Baroglie wavelength of two particle find the ratio in terms of symbols and then put the given numerical values.
5)
Calculate
(i) momentum and
(ii) de-Broglie wavelength of the electron accelerated through a potential difference of 56 V

CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits Ncert Exemplar 2 Mark Questions With Solutions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Explain why elemental semiconductor can not be used to make visible LEDs.
2)
In normal case, emitter-base junction is the forward bias and collector-base junction is reverse biased. What will happen if emitter is reverse biased and collector is forward biased?
3)
If the resistance R₁ is increased (see figure), how will the reading of the ammeter and voltmeter change?
4)
Write the truth for the circuit shown in figure below. Name the gate that the circuit resembles.
5)
A Zener of power rating 1 W is to be used as a voltage regulator. If Zener has a breakdown of 5 V and it has to regulate voltage which fluctuated between 3 V and 7 V, what should be the value of R_S for safe operations as shown below figure?

CBSE 12th Standard Physics Subject Communication Systems Ncert Exemplar 2 Mark Questions With Solutions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
A TV transmission tower antenna is at a height of 20 m. How much service area can it cover if the receiving antenna is
(i) at ground level,
(ii) at a height of 25 m?
Calculate the percentage increase in area covered in case (i) relative to case.
2)
The maximum frequency for reflection of sky waves from a certain layer of the ionosphere is found to be \({ f }_{ max }=9\left( { N }_{ max } \right) ^{ 1/2 }\), where N_maxis the maximum electron density at that layer of the ionosphere. On a certain day it is observed that signals of frequencies higher than 5 MHz are not received by reflection from the F₁ layer of the ionosphere while signals of frequencies higher than 8 MHz are not received by reflection from the F₂layer of the ionosphere. Estimate the maximum electron densities of the F₁and F₂ layers on that day.
3)
On radiating (sending out) an AM modulated signal, the total radiated power is due to the energy carried by \({ \omega }_{ c },{ \omega }_{ c }-{ \omega }_{ m }\) and Suggest ways to minimize the cost of radiation without compromising on information.
4)
A communication satellite is essentially a repeater station in space." Justify the statement by analysing the function of a repeater.
5)
What is space wave communication? Write the range of frequenices suitable for space wave communication.

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Ncert Exemplar 3 Mark Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
In the figure below the electric field lines on the left have twice the separation of those on the right.
(i) If the magnitude of the field of A is 40 N/C then what force acts on a proton at A?
(ii) What is the magnitude of the field at B?
2)
Five charges q each are placed at the corners of regular pentagon of side a as shown in the figure
(i) What wil be the electric field at O,the centre of the pentagon?

(b) what will be the electric field at O,if the charge from one of the corners(A) is removed?
(c) What will be electric field at O,if the charge q at A is replaced by -q?
(ii) How would your answer polygon with charge q at each of its corners?
3)
Two charges q₁ = +2 x 10^-8 C and q₂= -0.4 x 10^-8 C are placed 60 cm about, as shown in the figure. A third charge q₃ = 0.2 x 10^-8 C is moved along the arc of a circle of radius 80 cm from C to D. Compute the percentage change in the energy of the system.
4)
Figure shows two identical capacitors C₁ and C₂ ,each of 2\(\mu\) F capacitance, connected to a battery of 5 V. Initially switch S is closed. After sometimes, S is left open and dielectric slabs of dielectric constant K = 5 are inserted to fill completely the space between the plates of the two capacitors.How will the
(i) charge and
(ii) potential difference between the plates of the capacitors be affected after the slabs are inserted?
5)
In the circuit shown in figure, initially K₁ is closed and K₂ is opened. What are the charges on each of the capacitors? If K₁ was opened and K₂ was closed (order is important), what will be the charge on each capacitor now?
[Given, C = 1\(\mu F\)]

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Ncert Exemplar 3 Mark Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Three identical capacitors C₁,C₂ and C₃ of capacitance \(6\mu F\) each are connected to a 12V battery as shown. Find charge on each capacitor

Find
(i) the charge on each capacitor
(ii) the equivalent capacitances of the network
(iii) the energy stored in the network of capacitors.
2)
Which of the following figures cannot possibly represent electrostatic field lines?
3)
Figures (a) and (b) show the field lines of a positive and negative point charge respectively

(a) Give the signs of the potential difference V_P – V_Q; V_B – V_A.
(b) Give the sign of the potential energy difference of a small negative charge between the points Q and P; A and B.
(c) Give the sign of the work done by the field in moving a small positive charge from Q to P.
(d) Give the sign of the work done by the external agency in moving a small negative charge from B to A.
(e) Does the kinetic energy of a small negative charge increase or decrease in going from B to A?
4)
(a) Determine the electrostatic potential energy of a system consisting of two charges 7 μC and –2 μC (and with no external field) placed at (–9 cm, 0, 0) and (9 cm, 0, 0) respectively.
(b) How much work is required to separate the two charges infinitely away from each other?
(c) Suppose that the same system of charges is now placed in an external electric field E = A (1/r ²); A = 9 x 10⁵ NC^-1 m². What would the electrostatic energy of the configuration be?
5)
(a) A comb run through one’s dry hair attracts small bits of paper. Why?
What happens if the hair is wet or if it is a rainy day? (Remember, a paper does not conduct electricity.)
(b) Ordinary rubber is an insulator. But special rubber tyres of aircraft are made slightly conducting. Why is this necessary?
(c) Vehicles carrying inflammable materials usually have metallic ropes touching the ground during motion. Why?
(d) A bird perches on a bare high power line, and nothing happens to the bird. A man standing on the ground touches the same line and gets a fatal shock. Why?

CBSE 12th Standard Physics Subject Current Electricity Ncert Exemplar 3 Mark Questions With Solutions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
In a Wheatstone bridge circuit \(\rho =10\Omega \), \(Q=12\Omega \) and,\(R=8\Omega \) then find the value of S which is parallel to R.
2)
An aluminium wire of diameter 0.24cm is connected in series to a copper wire of diameter 0.16cm. The wires carry an electric current of 10A. Determine the current density in aluminium wire.
3)
The Wheatstone bridge circuit have the resistances in various arms as shown in figure. Calculate the current through the galvanometer.
4)
Write any two factors on which internal resistance of a cell depends. The reading on a high resistance voltmeter, when a cell is connected across it, is 2.2 V. When the terminals of the cell are also connected to a resistance of 5\(\Omega \) as shown in the circuit, the voltmeter reading drops to 1.8 V. Find the internal resistance of the cell.
5)
A potentiometer wire of length 1 m has a resistance of 10\(\Omega \). It is connected to 6 V battery in series with a resistance of 5\(\Omega \). Determine the emf of the primary cell, which gives a balance point at 40 cm.

CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits Ncert Exemplar 1 Mark Questions With Solutions 202 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Draw the output waveform across the resistor in the given figure
2)
In a CE transistor amplifier, there is a current and voltage again associated with the circuit.In other words, there is a power gain.Considering power a measure of energy, does the circuit violate conservation of energy?
3)
Write the truth table for the following circuit. Name the equivalent gate that this circuit.
4)
Sn, Cand Si, Ge are all group XIV elements. Yet, Sn is a conductor, Cis an insulator while Si and Ge are semiconductors. Why?
5)
Why are elemental dopants for silicon or germanium usually chosen from group XIII or group XV ?

CBSE 12th Standard Physics Subject Nuclei Ncert Exemplar 1 Mark Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Obtain approximately the ratio of the nuclear radii of the gold isotope \({ 79^{ Au } }^{ 197 }\) and the silver isotope \({ 79^{ Au } }^{ 197 }\)
2)
Draw a graph showing the variation of decay rate with number of active nuclei.
3)
\(_{ 2 }^{ 3 }{ He }\) and \(_{ 1 }^{ 3 }{ He }\) nuclei have the same mass number. Do they have same binding energy?
4)
Two nuclei have mass numbers in the ratio of 27:512. What is the ratio of their nuclear radii?
5)
\({ }_{2}^{3} \mathrm{He}\) and \({ }_{1}^{3} \mathrm{He}\) nuclei have the same mass number. Do they have same binding energy?

CBSE 12th Standard Physics Subject Dual Nature of Radiation and Matter Ncert Exemplar 1 Mark Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
A neutron beam of energy E scatters from atoms on a surface with a spacing d = 0.1nm. The first maximum of intensity in the reflected beam occurs at \(\theta =30°\) . What is the kinetic energy E of the beam in eV?
2)
For a given photosensitive material and with a source of constant frquency of incident radiation, how does the photocurrent vary with the intensity of incident light?
3)
Write the expression for the de-Broglie wavelength associated with a charged particle accelerated by a potential V.
4)
A proton and an electron have same kinetic energy. Which one has greater de-Broglie wavelength and why?
5)
Show graphically the variation of de-Broglie wavelength \(\lambda \) with the potential V through which an electron is accelerated from rest.
To plot the graph between the two quantities first of all we have to find the relation between the two through the connecting formula.

CBSE 12th Standard Physics Subject Wave Optics Ncert Exemplar 1 Mark Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
A boy is running towards a plane mirror with a speed of 2m|s. With what speed the image of the boy approach him?
2)
Two plane mirrors are inclined at an angle \(\theta \). It is found that a ray incident on one mirror at any angle rendered parallel to itself after reflection from both the mirrors. What will be the value of \(\theta \)?
3)
Given the effect on image, if lower half of the concave mirror is blackened.
4)
How can the real image of an object be obtained with a convex nirror?
5)
Why prisms are used in many optical instruments?

CBSE 12th Standard Physics Subject Wave Optics Ncert Exemplar 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Will the focal length of a lens for red light be more same or less than that for blue light?
2)
White light is incident on one of the refracting surface of a prism of angle 5⁰. If the refractive indices for red and blue colors are 1.641 and 1.659 respectively, then what will be the angular separation between these two colors when they emerge out?
3)
An unsymmetrical double convex thin lens forms the image of a point on its axis will the position of the image change is the lens are reversed?
4)
Which of the following waves can be polarised
(i) Heat waves or
(ii) Sound waves?
Give reason to support your answer.
5)
Why we cannot obtain interference using two independent sources of light?

CBSE 12th Standard Physics Subject Alternating Current Ncert Exemplar 1 Mark Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
The current through an AC circuit is \({ I }_{ t }={ I }_{ 0 }\left( t/\tau \right) \) for sometime. Determine the rms current through the circuit over time interval t = 0 to t =\(\tau\).
2)
The alternating current in a circuit is described by the graph shown in the figure. Find the rms current in this graph.
3)
Consider a magnet surrounded by a wire with an ON/OFF switch in the figure. If the switch is thrown from the OFF position (open circuit) to the ON position (closed circuit), will a current flow in the circuit? Explain.

The magnetic flux linked with a uniform surface area A in a uniform magnetic field is given by \(\phi \) = B.A = BA cos \(\theta \) .So flux linked will change, only when either B or A or the angle between B and A change.
4)
A train is moving with uniform speed from North and South, why will any induced emf appear across the ends of its axle?

CBSE 12th Standard Physics Subject Moving Charges And Magnetism Ncert Exemplar 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Among Biot-Savart's law and Coulomb's law which one is angle dependent?
2)
A bar magnet is cut into two equal parts as shown in the Fig. (a) One part is now kept over the other such that, the P₂is above P₁ as shown in the Fig.(b).
If M is the magnetic moment of the original magnet, what would be the magnetic moment of new combination of magnets so formed?
3)
Three identical bar magnets are rivetted together at centre in the same plane as shown in the figure. This system is placed at rest in a system is placed at rest in a slowly varying magnetic field. It is found that the system of magnets does not show any motion. The North-South poles of one magnet is shown in the figure. Determine the poles of the remaining two.
4)
A short magnet oscillates with a time period 0.1 s at a place, where horizontal magnetic field is \(24 \ \mu \)T.
A downward current of 18 A is established in a vertical wire 20cm East of the magnet. What will be the new time period of the oscillator?
5)
The horizontal component of the earth's magnetic field at a place is B and angle of dip is \(60^{ 0 }\) . What is the value of vertical component of earth's magnetic field at equator?

CBSE 12th Standard Physics Subject Moving Charges And Magnetism Ncert Exemplar 1 Mark Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Write the expression, in vector form, for the Lorentz magnetic force F due to a charge moving with velocity V in a magnetic field B. What is the direction of the magnetic force?
2)
A coil of N turns and radius R carries a current I. It is unwound and rewound to make a square coil of side a having same number of turns N.Keeping the currentI same, find the ratio of the magnetic moment of the square coil and the circular coil.
3)
Give the magnitude of torque which acts on a coil carrying current placed in a uniform radial magnetic field.
4)
Why is a coil wrapped on a conducting frame in a galvanometer?
5)
A bar magnet is cut into two equal parts as shown in the Fig. (a) One part is now kept over the other such that, the P₂is above P₁ as shown in the Fig.(b).
If M is the magnetic moment of the original magnet, what would be the magnetic moment of new combination of magnets so formed?

CBSE 12th Standard Physics Subject Current Electricity Ncert Exemplar 1 Mark Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
I-V graph for a metallic wire at two different temperature T₁ and T₂ is as shown in the figure below.

Which of the two temperatures is lower and why?
2)
Graphing showing the variation of current versus voltage for material Gaas is shown in the figure. Identify the region of

(i) negative resistance.
(ii) where Ohm's law is obeyed.
3)
In an experiment of meter bridge, the balancing length of the wire is l. What would be its value, if the radius of the meter bridge wire is double? Justify your answer.
4)
The emf of a cell is always greater than its terminal voltage. Why?
5)
A 10 V battery of negligible internal resistance is connected across a 200 V battery and a resistance of 38 \(\Omega \) as shown in the figure. Find the value of the current in the circuit.

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Ncert Exemplar 1 Mark Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Does the coulomb force that one charge exerts on another charge changes, if other charge is brought nearly?
2)
The test charge used to measure electric field at a point should be vanishingly small.Why?
3)
Why electrostatic field be normal to the surface at every point of a charged conductor?
4)
An electrostatic field line is continuous curve, i.e. a field line cannot have sudden breaks. Why not?
5)
Force experienced by an electron in an electric field is F newton. What will be the force experienced by a proton in the same field? take mass of a proton is 1836 times the mass of an electron.

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Ncert Exemplar 1 Mark Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Two point charges of + 3\(\mu \)C each are 100 cm apart.At what point on the line joining the charges will the electric field intensity be zero?
2)
Why should electrostatic field be zero inside a conductor?
3)
why do the electric field lines not form closed loops?
4)
The dimension of an atom are of the order of an angstrom. Thus, there must be large electric fields between the protons and electrons. Why, then is the electrostatic field inside a conductor zero?
5)
A Metallic spherical shell has an inner radius R₁ and outer radius R_2.A charge Q is placed at the center of the spherical cavity.what will be surface charge density (i)the inner surface and (ii)the outer surface?

CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits Ncert Exemplar MCQ Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
In the depletion region of a diode
2)
What happens during regulation action of a zener diode?
3)
To reduce the ripples in rectfier circuit with capacitor filter
4)
The breakdown in a reverse biased p-n junction is more likely to occur due to
5)
A 220 V AC supply is connected between points A and B (figure). What will be the potential difference V across the capacitor?

CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits Ncert Exemplar MCQ Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
The conductivity of a semiconductor increases with increase in temperature because
2)
Hole is
3)
When an electric field is applied across a semiconductor
4)
Consider an npn transistor with its base emitter junction forward biased and collector base junction reverse biased. Which of the following statements are true?
5)
In a npn transisitor circuit,the collector current is 10 mA. If 95 percent of the electrons emitted reach the collector,which of the following statements are true?

CBSE 12th Standard Physics Subject Nuclei Ncert Exemplar MCQ Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
O₂ molecule consists of two oxygen atoms.In the molecule, nuclear force between the nuclei of the two atoms
2)
The gravitational force between a H-atom and another particle' of mass m will be given by Newton's law \(F=G \frac{M m}{r^{2}}\), where r is in km
3)
When a nucleus in an atom undergoes a radioactive decay, the electronic energy levels of the atom
4)
In a nuclear reactor, moderators slow down the neutrons which come out in a fission process. The moderator used have light nuclei. Heavy nuclei will not serve the purpose, because
5)
In fusion reaction occurring in the sun,

CBSE 12th Standard Physics Subject Atoms Ncert Exemplar MCQ Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
For the ground state, the electron in the H-atom has an angular momentum =h, according to the simple Bohr model. Angular momentum is a vector and hence there will be infinitely many orbits with the vector pointing in all possible directions. In actuality, this is not true,
2)
An ionised H-molecule consists of an electron and two protons. The protons are separated by a small distance of the order of angstrom. In the ground state
3)
Consider aiming a beam of free electrons towards free protons. When they scatter, an electron and a proton cannot combine to produce a H-atom,
4)
The Bohr model for the spectre of a H-atom
5)
The Balmer series for the H-atom can be observed

CBSE 12th Standard Physics Subject Atoms Ncert Exemplar MCQ Questions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Taking the Bohr radius as a₀ = 53pm, the radius of Li⁺⁺ ion its ground state, on the basis of Boh''s model, will be about
2)
The simple Bohr model cannot be directly applied to calculate the energy levels of an atom with electrons. This because
3)
For the ground state, the electron in the H-atom has an angular momentum =h, according to the simple Bohr model. Angular momentum is a vector and hence there will be infinitely many orbits with the vector pointing in all possible directions. In actuality, this is not true,
4)
Two H atoms in the ground state collide inelastically kinetic energy is reduced is
5)
A set of atoms in an excited state decays

CBSE 12th Standard Physics Subject Dual Nature of Radiation and Matter Ncert Exemplar MCQ Questions With Solutions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
A particle is dropped from a height H. The de Broglie wavelength of the particle as a function of height is proportional to
2)
The wavelength of a photon needed to remove a proton from a nucleus which is bound to the nucleus with 1 MeV energy is nearly,
3)
Consider a beam of electrons (each with energy E₀) incident on a metal surface kept in an evacuated chamber. Then
4)
Two particles A₁ and A₂ masses m₁, m₂ (m₁>m₂) have the same de Broglie wavelength. Then
5)
Consider a beam of electrons (each electron with energy Eo) incident on a metal surface kept in an evacuated chamber. Then

CBSE 12th Standard Physics Subject Electric Charges And Fields Ncert Exemplar MCQ Questions With Solutions 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
In figure two positive charges q₂and q₃ fixed along the y-axis, exert a net electric force in the + x- direction on a charge q₁ fixed along the x-axis. If a positive charge Q is added at (x, 0), the force on q₁
2)
A point positive charge is brought near an isolated conducting sphere (figure). The electric field is best given by
3)
A hemisphere is uniformly charged. The electric field at a point on a diameter away from the centre is directed
4)
A point charge + q is placed at a distance d from an isolated conducting plane. The field at a point P on the other side of the plane is
5)
Figure shows electric field lines in which an electric dipole P is placed as shown. Which of the following statements is correct?

CBSE 12th Standard Physics Subject Ncert Exemplar 5 Marks Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
In Pradeep's classroom, the fan was running very slowly. Due to which, his teacher was sweating and was restless and tired.All his classmates wanted to rectify this. They called an electrician who came and changed the capacitor only, after which the fan started running fast.
Answer the following questions based on the above information:
(i) What energy is stored in the capacitor and where?
(ii) A thin metal sheet is placed in the middle of a parallel plate capacitor. What will be the effect on the capacitance?
(iii) What values did the classmates have?
2)
(i) In a meter bridge, the balance point is found to be at 39.5 cm from the end A, if an unknown resistor X is in the left gap and a known resistor Y of resistance 1.25 \(\Omega\) is in the right gap. Determine resistance of X. Why are the connections between resistors in a Wheatstone or meter bridge made of thick copper strips?
(ii) Determine the balance point of the above bridge, if X and Y are interchanged.
(iii) What happens, if the galvanometer and cell are interchanged at the balance point of the bridge? would the galvanometer show any current?
3)
Explain using a labelled diagram, the principle and working of a moving coil galvanometer. What is the function of
(i) uniform radial magnetic field
(ii) soft iron core?
Also, define the terms
(iii) current sensitivity and
(iv) voltage sensitivity of a galvanometer.
Why does increasing the current sensitivity not necessarily increase voltage sensitivity?
4)
In the birthday party of Kamal, his parents gave big slinkies to all his friends as a return gift. The very next day, during the physics class Mr. Mohan, the teacher explained them about the production of magnetic field using current carrying coil and also said that they can make permanent magnet, using such coils by passing high currents through them. That night Priyanshu, a friend of Kamal, asked his father about the coils, and their shape. His father asked him to bring the slinky, that his friend gave and explained the use of toroid and solenoid.
Read the above passage and answer the following questions:
(i) What value did Priyanshu's father have?
(ii) What is the difference between solenoid and toroid?
(iii) Give the value or magnitude of magnetic field in solenoid.
5)
Niyaz was using galvanometer in the practical class. Unfortunately, it fell from his hand and broke. He was upset, some of his friends advised him not to tell the teacher but Niyaz decided to tell his teacher. Teacher listened to him patiently and on knowing that the act was not intentional, but just an accident, did not scold him and used the opportunity to show the internal structure of galvanometer.
(i) What are the values displayed by Niyaz?
(ii) Give the principle of moving coil galvanometer.
(iii) How can you increase the sensitivity of a galvanometer?

CBSE 12th Standard Physics Subject Ncert Exemplar 5 Marks Questions 2021 Part - II - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Given figure shows a charge array known as an electric quadrupole. For a point on the axis of the quadrupole, obtain the dependence of potential on r for r/a>>1 and contrast your results with that due to an electric dipole and an electric monopole(i.e. a single charge).
2)
The unknown resistance of a conductor can be determined by Wheatstone bridge. The standard form of Wheatstone bridge is shown in the figure. It can be shown when the bridge is balanced.

\(\frac { P }{ Q } =\frac { R }{ S } \quad or\quad S=\frac { Q }{ P } R\)
Knowing P,Q and R, unknown resistance S can be calculated.
Read the above passage and answer the following questions.
(i) Name any two applications of Wheatstone bridge.
(ii) What is the practical utility of the post office box in day to day life?
3)
A resistance of R \(\Omega \) draws current from a potentiometer as shown in the figure. The potentiometer has a total resistance R₀ \(\Omega\). A voltage V is supplied to the potentiometer. Derive an expression for the voltage across R, when the sliding contact is in the middle of the potentiometer.
4)
Explain using a labelled diagram, the principle and working of a moving coil galvanometer. What is the function of
(i) uniform radial magnetic field
(ii) soft iron core?
Also, define the terms
(iii) current sensitivity and
(iv) voltage sensitivity of a galvanometer.
Why does increasing the current sensitivity not necessarily increase voltage sensitivity?
5)
(i) Derive the expression for the torque on a rectangular current carrying loop suspended in a uniform magnetic field
(ii) A proton and a deuteron having equal momentum enter in a region of a uniform magnetic field at right angle to the direction of the field.Depict their trajectories in the field

CBSE 12th Standard Physics Subject Ncert Exemplar 5 Marks Questions 2021 Part - I - by Sharma - Kochi - May 22, 2021 - View & Read

1)
If one of the electrons of H₂ molecules is removed, we get a hydrogen molecular ion H⁺₂ . In the ground state of an H⁺₂, the two protons are separated by roughly 1.5 \(\overset { o }{ A } \) and the electron is roughly 1\(\overset { o }{ A } \) from each proton. Determine the potential energy of the system. Specify your choice of the zero of potential energy.
2)
The electric field at a point on the axial line at a distance of 10 cm from the center of an electric dipole is 3.75\(\times\) N/C. Calculate the length of an electric dipole.
3)
Given figure shows a charge array known as an electric quadrupole. For a point on the axis of the quadrupole, obtain the dependence of potential on r for r/a>>1 and contrast your results with that due to an electric dipole and an electric monopole(i.e. a single charge).
4)
The unknown resistance of a conductor can be determined by Wheatstone bridge. The standard form of Wheatstone bridge is shown in the figure. It can be shown when the bridge is balanced.

\(\frac { P }{ Q } =\frac { R }{ S } \quad or\quad S=\frac { Q }{ P } R\)
Knowing P,Q and R, unknown resistance S can be calculated.
Read the above passage and answer the following questions.
(i) Name any two applications of Wheatstone bridge.
(ii) What is the practical utility of the post office box in day to day life?
5)
A resistance of R \(\Omega \) draws current from a potentiometer as shown in the figure. The potentiometer has a total resistance R₀ \(\Omega\). A voltage V is supplied to the potentiometer. Derive an expression for the voltage across R, when the sliding contact is in the middle of the potentiometer.

CBSE 12th Standard Physics Subject Ncert Exemplar 3 Marks Questions 2021 Part - I - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Figure shows the electric field lines around three point charges A, B and C

(i) Which charges are positive?
(ii) Which charge has the largest magnitude? Why?
(iii) In which region or regions of the picture could the electric field be zero? Justify your answer.
(a) Near A
(b) Near B
(c) Near C
(d) Nowhere
2)
An electric dipole of length 2 cm, when placed with its axis making an angle of 60^o with a uniform electric field, experiences a torque of \(8\sqrt { 3 } \)N-m. Calculate the potential energy of the dipole, if it has a charge of \(\pm \)4nC.
3)
Explain why the following curves cannot possibly represent electrostatic field lines?
4)
Figure shows the electric field lines around three point charges A, B and C.

(i) Which charges are positive?
(ii) Which charge has the largest magnitude?
(iii) In which region or regions of the picture could the electric field be zero? Justify your answer.
(a) Near A
(b) Near B
(c) Near C
(d) Near D
(i) Electric field lines always start from a positive charge and end at a negative charge. In case of a single charge, electric lines of force start from positive charge and end at infinity.
(ii) The magnitude of a charge depends on the number of lines of force emanating from a charge, i.e higher the number of lines of force, higher the magnitude of charge and vice-versa.
5)
Figure represents a crystal unit of caesium chloride,CsCl. The caesium automs,represented by open circles are situated at the corners of a cube of side 0.40 nm, whereas a CI atom is situated at the centre of the cube. The Cs atoms are deficient in one electron while the CI atom carrieres an excess electron.

(i) What is the net electric field on the CI atom dur to eight Cs atoms?
(ii) Suppose that the Cs atom at the corner A is missing.What is the net force now on the CI atom due to seven remaining Cs atoms?
(i) Net force on a charge due to two equal and opposite charges will be zero.Also electric field on a charge is given by
E = F / Q
where E=electric field, F = force on change q due to electric field and q = magnitude of charge.
(ii) If a Cs atom is removed from the corner A, then a singly charged Cs ion at A will appear.

CBSE 12th Standard Physics Subject Ncert Exemplar 3 Marks Questions 2021 Part - II - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Draw the output signals C₁ in the given combination of gates.
2)
A student has to use an appropriate number of
(i) NAND gates (only) to get the output Y₁
(ii) NOR gates (only) to get the output Y₂
From two given inputs A and B as shown in the diagram.

Identify the 'equivalent gate' needed in each case.Show how one can connect an appropriate number of (i) NAND (ii) NOR gates respectively in the two cases to get these' equivalent gates'.
3)
The graph of potential barrier versus width of depletion region for an unbiased diode is shown in A. In comparison to A, graphs B and C are obtained after biasing the diode in different ways. Identify the type of biasing in B & C and justify your answer.

Explain why:
LEDs are made of compound semiconductor and not by elemental semiconductors.
4)
Calculate the length of quarter wave antenna for transmission frequency of 20 MHz

CBSE 12th Standard Physics Subject Ncert Exemplar 3 Marks Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Figure shows the electric field lines around three point charges A, B and C

(i) Which charges are positive?
(ii) Which charge has the largest magnitude? Why?
(iii) In which region or regions of the picture could the electric field be zero? Justify your answer.
(a) Near A
(b) Near B
(c) Near C
(d) Nowhere
2)
An electric dipole of length 2 cm, when placed with its axis making an angle of 60^o with a uniform electric field, experiences a torque of \(8\sqrt { 3 } \)N-m. Calculate the potential energy of the dipole, if it has a charge of \(\pm \)4nC.
3)
A charge q is placed at the center of a cube of side l. What is the electric passing through each of the cube?
4)
In the figure below the electric field lines on the left have twice the separation of those on the right.
(i) If the magnitude of the field of A is 40 N/C then what force acts on a proton at A?
(ii) What is the magnitude of the field at B?
5)
Show that the force on each plate of a parallel plate capacitor has a magnitude equal to1/2 QE. where Q is the charge on the capacitor and E is the magnitude of electric field between the plates. Explain the origin of the factor 1/2.
Here, we can use the content that the work done in displacing the plates against the force is equal to the increase in energy of the capacitor.

CBSE 12th Standard Physics Subject Ncert Exemplar 2 Marks Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
A bird perches on a bare high power line and nothing happens to the bird. A man standing on the ground touches the same line and gets a fatal shock why?
2)
AB is a potentiometer wire as shown in figure. If the value of R is increased, in which direction will the balance point J shift?
3)
Suppose we want to verify the analogy between electrostatic and magnetic by an explicit experiment. Consider the motion of
(i) electric dipole p in an electrostatic field E and
(ii) magnetic dipole M in a magnetic field B. Write down a set of conditions on E,B,p,M so that the two motions are verified to be identical.(assume idential initial conditions)
E(r) = cB(r), suppose the angle between p and E is \(\theta \) . Torque on electric dipole moment M in magnetic field E, \(\tau =pEsin\theta \)
4)
A ball of superconducting matesial is dipped in liquid nitrogen and placed near a bar magnet.
(i) In which direction will it move?
(ii) What will be the direction of its magnetic moment?
5)
(i) A metal ring is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring. What will be the acceleration of a falling magnet?
(ii) Consider a metal ring kept on top of a fixed solenoid (say on cardboard) (see figure). The center of the ring coincides with the axis of the solenoid. If the current is suddenly switched ON, the metal ring jumps up. Explain.

CBSE 12th Standard Physics Subject Ncert Exemplar 2 Marks Questions 2021 Part - II - by Sharma - Kochi - May 22, 2021 - View & Read

1)
A paisa coin is made up of AI-Mg alloys and weighs 0.75 g. It has a square shape and its diagonal measures 17 mm. It is electrically neutral and contains equal amount of positive and negative charges. Treating the paisa coins made up of only AI, find the magnitude of equal number of positive and negative charges. What conclusion do you draw from this magnitude?
2)
A and B have identical size and same mass. A becomes A²⁺ and B become B^2- . Will A²⁺ and B^2- still have the same mass? Why?
3)
Two charges 2 \(\mu \)C and -2\(\mu \) C are placed at points A and B, 6 cm apart. What is the direction of the electric field at every point on this surface?
4)
First a set of n equal resistors of R each are connected in series to a battery of emf E and internal resistance R and current I is observed to flow. Then, the resistors are connected in parallel to the same battery. It is observed that the current is increased 10 times. What is n?
5)
A short bar magnet has a magnetic moment of 0.48 J/T. Give the direction and magnitude of the magnetic field produced by the magnet at a distance of 10cm from the centre of the magnet on
(i) the axis,
(ii) the equatorial lines (normal bisector) of the magnet.

CBSE 12th Standard Physics Subject Ncert Exemplar 2 Marks Questions 2021 Part - I - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Sketch the electric field lines for a uniformly charged hollow cylinder as shown in the figure.
2)
Sketch the electric field lines for a uniformly charged hollow cylinder as shown in the figure.
3)
Two identical plane metallic surfaces A and B are kept parallel to each other in air, separated by a distance of 1 cm, surface A is given a positive potential of 10 V and the outer surface of B is earthed.
(i) What is the magnitude and direction of the electric field between the planes A and B?
(ii) What is the work dine in moving a charge of 20\(\mu \)C from plane A to plane B?
4)
The circular arc is shown in the figure given below, has a uniform charge per unit length of 1 x 10^-8C/m. Find the potential at the centre O of the arc.
5)
In a meter bridge, the null point is found at a distance of 33.7 cm from A. If a resistance of 12\(\Omega \) is connected in parallel with S, the null point occurs at 51.9 cm. Determine the values of R and S.

CBSE 12th Standard Physics Subject Ncert Exemplar 1 Marks Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
Two point charges of + 3\(\mu \)C each are 100 cm apart.At what point on the line joining the charges will the electric field intensity be zero?
2)
If an electric dipole is placed in a uniform electric field, then state whether it always experience a torque or not?
3)
Graphing showing the variation of current versus voltage for material Gaas is shown in the figure. Identify the region of

(i) negative resistance.
(ii) where Ohm's law is obeyed.
4)
A coil of N turns and radius R carries a current I. It is unwound and rewound to make a square coil of side a having same number of turns N.Keeping the currentI same, find the ratio of the magnetic moment of the square coil and the circular coil.
5)
Three identical bar magnets are rivetted together at centre in the same plane as shown in the figure. This system is placed at rest in a system is placed at rest in a slowly varying magnetic field. It is found that the system of magnets does not show any motion. The North-South poles of one magnet is shown in the figure. Determine the poles of the remaining two.

CBSE 12th Standard Physics Subject Ncert Exemplar 1 Marks Questions 2021 Part - II - by Sharma - Kochi - May 22, 2021 - View & Read

1)
An arbitrary surface encloses a dipole. What is the electric flux through this surface?
2)
Why electrostatic field be normal to the surface at every point of a charged conductor?
3)
The dimension of an atom are of the order of an angstrom. Thus, there must be large electric fields between the protons and electrons. Why, then is the electrostatic field inside a conductor zero?
4)
If an electric dipole is placed in a uniform electric field, then state whether it always experience a torque or not?
5)
The safest way to protect yourself from lightning is to be inside a car. Comment.

CBSE 12th Standard Physics Subject Ncert Exemplar 1 Marks Questions 2021 Part - I - by Sharma - Kochi - May 22, 2021 - View & Read

1)
A metallic spherical shell has an inner radius R₁ and outer radius R₂. A charge Q is placed at the centre of the spherical cavity. What will be surface charge density on
(i) the inner surface and
(ii) the outer surface
2)
Does the coulomb force that one charge exerts on another charge changes, if other charge is brought nearly?
3)
The dimension of an atom are of the order of an angstrom. Thus, there must be large electric fields between the protons and electrons. Why, then is the electrostatic field inside a conductor zero?
4)
Two point charges having equal charges separated by 1 m distance experienced a force of 8 N.What will be the force experienced by them,if they are held in water, at the same distance?(Given K_water =80)
5)
A dipole of dipole moment p is present uniform electric field E . Write the value of the angle between p and E for which the torque, experienced by the dipole in minimum.

CBSE 12th Standard Physics Subject Ncert Exemplar MCQ Questions With Solution 2021 - by Sharma - Kochi - May 22, 2021 - View & Read

1)
A hemisphere is uniformly charged. The electric field at a point on a diameter away from the centre is directed
2)
The electrostatic potential on the surface of a charged conducting sphere is 100 V. Two statements are made in this regard S₁ at any point inside the sphere, electric intensity is zero. S₂ at any point inside the sphere, the electrostatic potential is 100 V. Which of the following is a correct statement?
3)
A resistance R is to be measured using a meter bridge, student chooses the standard resistance S to be won. He finds the null point at l, = 2.9 em. He is told to attempt to improve the accuracy. Which of the following is a useful way?
4)
If the rms current in a 50 Hz AC circuit is 5 A, the value of the current 1/300 s after its value becomes zero is
5)
Consider a beam of electrons (each with energy E₀) incident on a metal surface kept in an evacuated chamber. Then

CBSE 12th Standard Physics Subject Ncert Exemplar MCQ Questions 2021 Part - II - by Sharma - Kochi - May 22, 2021 - View & Read

1)
A point positive charge is brought near an isolated conducting sphere (figure). The electric field is best given by
2)
A capacitor of 4\(\mu\)F is connected as shown in the circuit. The internal resistance of the battery is 0.5\(\Omega \). The amount of charge on the capacitor plates will be
3)
Two batteries of emf ε₁ and ε₂, (ε₂ >ε₁) and internal resistances r₁and r₂ respectively are connected in parallel as shown in figure.
4)
There are two coils and B as shown in figure. A current starts flowing in B as shown, when A is moved towards B and stops when A stops moving. The current in A is counter clockwise. B is kept stationary when A moves. We can infer that
5)
When a voltage measuring device is connected to AC mains, the meter shows the steady input voltage of 220 V. This means

CBSE 12th Standard Physics Subject Ncert Exemplar MCQ Questions 2021 Part - I - by Sharma - Kochi - May 22, 2021 - View & Read

1)
In figure two positive charges q₂and q₃ fixed along the y-axis, exert a net electric force in the + x- direction on a charge q₁ fixed along the x-axis. If a positive charge Q is added at (x, 0), the force on q₁
2)
A hemisphere is uniformly charged. The electric field at a point on a diameter away from the centre is directed
3)
Figure shows electric field lines in which an electric dipole P is placed as shown. Which of the following statements is correct?
4)
Figure shows some equipotential lines distributed in space. A charged object is moved from point A to point B.
5)
Two cells of emfs approximately 5 V and l0 V are to be accurately compared using a potentiometer of length 400 cm.

CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits Chapter Case Study Questions 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
When the diode is forward biased, it is found that beyond forward voltage V = V_k, called knee voltage, the conductivity is very high. At this value of battery biasing for p-n junction,the potential barrier is overcome and the current increases rapidly with increase in forward voltage. When the diode is reverse biased, the reverse bias voltage produces a very small current about a few microamperes which almost remains constant with bias. This small current is reverse saturation current.
(i) In which of the following figures, the p-n diode is forward biased.

(ii) Based on the V-I characteristics of the diode, we can classify diode as

(a) bi-directional device (b) ohmic device

(c) non-ohmic device (d) passive element

(iii) The V-I characteristic of a diode is shown in the figure. The ratio of forward to reverse bias resistance is

(a) 100 (b) 10⁶ (c) 10 (d) 10^-6

(iv) In the case of forward biasing of a p-n junction diode, which one of the following figures correctly depicts the direction of conventional current (indicated by an arrow mark)?

(v) If an ideal junction diode is connected as shown, then the value of the current I is

(a) 0.013 A (b) 0.02 A (c) 0.01 A (d) 0.1 A

2)

Rectifier is a device which is used for converting alternating current or voltage into direct current or voltage. Its working is based on the fact that the resistance of p-n junction becomes low when forward biased and becomes high when reverse biased. A half-wave rectifier uses only a single diode while a full wave rectifier uses two diodes as shown in figures (a) and (b) .

(i) If the rms value of sinusoidal input to a full wave rectifier is \(\frac{V_{0}}{\sqrt{2}}\) then the rms value of the rectifier's output is

\(\text { (a) } \frac{V_{0}}{\sqrt{2}}\)

\(\text { (b) } \frac{V_{0}^{2}}{\sqrt{2}}\)

\(\text { (c) } \frac{V_{0}^{2}}{2}\)

\(\text { (d) } \sqrt{2} V_{0}^{2}\)

(ii) In the-diagram, the input ac is actoss the terminals A and C. The output across Band D is

(a) same as the input

(b) half wave rectified

(c) zero

(d) full wave rectified

(iii) A bridge rectifier is shown in figure. Alternating input is given across A and C. If output is taken across BD, then it is

(a) zero

(b) same as input

(c) half wave rectified

(d) full wave rectified

(iv) A p-n junction (D) shown in the figure can act as a rectifier. An alternating current source (V) is connected in the circuit. The current (I) in the resistor(R) can be shown by

(v) With an ac input from 50 Hz power line, the ripple frequency is

(a) 50 Hz in the dc output of half wave as well as full wave rectifier

(b) 100 Hz in the de output of half wave as well as full wave rectifier

(c) 50 Hz in the de output of half wave and 100 Hz in dc output offull wave rectifier

(d) 100 Hz in the dc output of half wave and 50 Hz in the de output of full wave rectifier

3)

From Bohr's atomic model, we know that the electrons have well defined energy levels in an isolated atom. But due to interatomic interactions in a crystal, the electrons of the outer shells are forced to have energies different from those in isolated atoms. Each energy level splits into a number of energy levels forming a continuous band.The gap between top of valence band and bottom of the conduction band in which no allowed energy levels for electrons can exist is called energy gap.

(i) In an insulator energy band gap is

(a) E_g = 0

(b) E_g< 3eV

(c) E_g> 3eV

(d) None of the above

(ii) In a semiconductor, separation between conduction and valence band is of the order of

(a) 0 eV

(b) 1 eV

(c) 10 eV

(d) 50 eV

(iii) Based on the band theory of conductors, insulators and semiconductors, the forbidden gap is smallest in

(a) conductors

(b) insulators

(c) semiconductors

(d) All of these

(iv) Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?

(a) The number of free electrons for conduction is significant only in Si and Ge but small in C.

(b) The number of free conduction electrons is significant in C but small in Si and Ge.

(c) The number of free conduction electrons is negligibly small in all the three.

(d) The number offree electrons for conduction is significant in all the three.

(v) Solids having highest energy level partially filled with electrons are

(a) semiconductor

(b) conductor

(c) insulator

(d) none of these

4)

Light emitting diode is a photoelectric device which converts electrical energy into light energy. It is a heavily doped p-n junction diode which under forward biased emits spontaneous radiation. The general shape of the J- V characteristics of an LED is similar to that of a normal p-n junction diode, as shown. The barrier potentials are much higher and slightly different for each colour.

(i) The J- V characteristic of an LED is

(ii) The schematic symbol of light emitting diode is (LED)

(iii) An LED is constructed from a p-n junction based on a certain Ga-As-P semiconducting material whose energy gap is 1.9 eV. Identify the colour of the emitted light.

(a) Blue

(b) Red

(c) Violet

(d) Green

(iv) Which one of the following statement is not correct in the case of light emitting diodes?

(a) It is a heavily doped p-n junction.

(b) It emits light only when it is forward biased.

(c) It emits light only when it is reverse biased.

(d) The energy of the light emitted is less than the energy gap of the semiconductor used

(v) The energy of radiation emitted by LED is

(a) greater than the band gap of the semiconductor used

(b) always less than the band gap of the semiconductor used

(c) always equal to the band gap of the semiconductor used

(d) equal to or less than the band gap of the semiconductor used.

5)

A photodiode is an optoelectronic device in which current carriers are generated by photons through photoexcitation i.e., photo conduction by light. It is a p-n junction fabricated from a photosensitive semiconductor and provided with a transparent window so as allow light to fall on its function. A photodiode can turn its current ON and OFF in nanoseconds. So, it can be used as a fastest photo-detector.

(i) A p-n photo diode is fabricated from a semiconductor with a band gap of 2.5 ev' It can detect a signal of wavelength

(a) 4000 nm

(b) 6000 nm

(c) 4000 \(\dot A\)

(d) 6000 \(\dot A\)

(ii) Three photo diodes D₁ D₂ and D₃ are made of semiconductors having band gap of 2.5 eV, 2 eV and 3 eV, respectively. Which one will be able to detect light of wavelength 6000 \(\dot A\) ?

(a) D₁

(b) D₂

(c) D₃

(d) D₁, and D₂ both

(iii) Photodiode is a device

(a) which is always operated in reverse bias

(b) which of always operated in forward bias

(c) in which photo current is independent of intensity of incident radiation

(d) which may be operated in forward or reverse bias.

(iv) To detect light of wavelength 500 nrn, the photodiode must be fabricated from a semiconductor of minimum bandwidth of

(a) 1.24 eV

(b) 0.62 eV

(c) 2.48eV

(d) 3.2 eV

(v) Photo diode can be used as a photo detector to detect

(a) optical signals

(b) electrical signals

(c) both (a) and (b)

(d) none of these

CBSE 12th Standard Physics Subject Dual Nature of Radiation and Matter Chapter Case Study Questions 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
Photoelectric effect is the phenomenon of emission of electrons from a metal surface, when radiations of suitable frequency fallon them. The emitted electrons are called photoelectrons and the current so produced is called photoelectric current.
(i) With the increase of intensity of incident radiations on photoelectrons emitted by a photo tube, the number of photoelectrons emitted per unit time is

(a) increases (b) decreases

(c) remains same (d) none of these

(ii) It is observed that photoelectron emission stops at a certain time t after the light source is switched on. The stopping potential (V) can be represented as

(a) 2(KE_max/e) (b) (KE_max/e)

(c) (KE_max/3e) (d) (KE_max/2e)

(iii) A point source of light of power 3.2 x 10^-3 W emits monoenergetic photons of energy 5.0 eV and work function 3.0 eV. The efficiency of photoelectron emission is 1 for every 10⁶ incident photons. Assume that photoelectrons are instantaneously swept away after emission. The maximum kinetic energy of photon is

(a) 4 eV (b) 5 eV

(c) 2 eV (d) Zero

(iv) Which of the following device is the application of Photoelectric effect?

(a) Light emitting diode (b) Diode

(c) Photocell (d) Transistor

(v) If the frequency of incident light falling on a photosensitive metal is doubled, the kinetic energy of the emitted photoelectron is

(a) unchanged (b) halved

(c) doubled (d) more than twice its initial value
2)
When a monochromatic radiations of suitable frequency obtained from source S, after being filtered by a filter attached on the window W, fall on the photosensitive place C, the photo electrons are emitted from C, which get accelerated towards the plate A if it is kept at positive potential. These electrons flow in the outer circuit resulting in photoelectric current. Due to it, the micro ammeter shows a deflection. The reading of micrommeter measures the photoelectric current.

An experimental setup of verification of photoelectric effect is shown in figure. The voltage across the electrodes is measured with the help of an ideal voltmeter, and which can be varied by moving jockey J on the potentiometer wire. The battery used in potentiometer circuit is of 16 V and its internal resistance is 2 \(\Omega\) The resistance of 100 ern long po.t•e. ntiometer wire is 8 \(\Omega\).

The photocurrent is measured with the help of an ideal ammeter. Two plates of potassium oxide of area 50 cm² at separation 0.5 mm are used in the vacuum tube. Photocurrent in the circuit is very small, so we can treat the
potentiometer circuit as an independent circuit

Light Violet blue Green Yellow Orange Red

\(\lambda\) in \(\dot A\) 4000-5000 4500-5000 5000-5500 5500-6000 6000-6500 6500-7000

(i) When radiation falls on the cathode plate, a current of 2 \(\mu \)A is recorded in the ammeter. Assuming that the vacuum tube setup follows Ohm's law, the equivalent resistance of vacuum tube operating in the case when jockey is at end P is

(a) 8 x 10⁸\(\Omega\) (b) 16 x 10⁶\(\Omega\) (c) 8 x 10⁶\(\Omega\) (d) 10 x 10⁶\(\Omega\)

(ii) It is found that ammeter current remains unchanged (2 \(\mu\)A) even when the jockey is moved from the end P to the middle point of the potentiometer wire. Assuming that all the incident photons eject electrons and the power of the light incident is 4 x 10^-6\(\Omega\)Then, the color of the incident light is

(a) Green (b) Violet (c) Red (d) Orange

(iii) Which of the following colors may not give photoelectric effect for this cathode?

(a) Green (b) Violet (c) Red (d) Orange

(iv) When other light falls on the anode plate, the ammeter reading zero till jockey is moved from the end P to the middle point of the wire PQ. Therefore, the deflection is recorded in the ammeter. The maximum kinetic energy of the emitted electron is

(a) 16 eV (b) 8 eV (c) 4 eV (d) 10 eV

(v) If the intensity of incident radiation is increased twice, the number of photoelectrons emitted per second will be

(a) halves (b) double (c) remain same (d) four times
3)
A point source S of power 6.4 x 10^-3W emits mono energetic photons each of energy 6.0 eV. The source is located at a distance of 0·8 m from the centre of a stationary metallic sphere of work function 3·0 eV and of radius 1.6 x 10^-3 m as shown in figure. The sphere is isolated and initially neutral and photoelectrons are instantly taken away from sphere after emission. The efficiency of photoelectric emission is one for very 10⁵ incident photons.

(i) The'power received by the sphere through radiations is

\(\text { (a) } \frac{4 R^{2}}{P r}\) \(\text { (b) } \frac{P R^{2}}{4 r^{2}}\) \(\text { (c) } \frac{p^{2} R}{2 \pi r}\) \(\text { (d) } \frac{P R}{4 r}\)

(ii) Number of photons striking the metal sphere per second is

(a) 6.7 x 10⁹ (b) 3.3 x 10⁹ (c) 6.7 x 10¹⁰ (b) 3.3 x 10¹⁰

(iii) The number of photoelectrons emitted per second is about

(a) 3.3 x 10⁴ (b) 6.7 x 10⁴ (c) 6.7 x 10¹⁵ (d) 3.3 x 10¹⁵

(iv) The photoelectric emission stops when the sphere acquires a potential about

(a) 2 V (b) 3 V (c) 4 V (d) 6 V

(v) If the distance of source becomes double from the centre of the metal sphere then the power received by the sphere

\(\text { (a) } \frac{P R^{2}}{4 r^{2}}\) \(\text { (b) } \frac{P R^{2}}{16 r^{2}}\) \(\text { (c) } \frac{P R^{2}}{4 r}\) \(\text { (d) } \frac{P^{2} R^{2}}{16 r^{2}}\)

4)

According to Einstein, when a photon of light of frequency u or wavelength \(\lambda\) is incident on a photosensitive metal surface of work function \(\phi\)₀w' here \(\phi\)₀< hv (here, h is Planck's constant), then the emission of photoelectrons takes place. The maximum kinetic energy of the emitted photoelectrons is given by K_max = hv - \(\phi\)₀. If the frequency of the incident light is V₀called threshold frequency, the photoelectrons are emitted from metal without any kinetic energy. So hv₀ = \(\phi\)
(i) A metal of work function 3·3 eV is illuminated by light of wavelength 300 nm. The maximum kinetic energy of photoelectrons emitted is (taking h = 6·6 x 10^-34 Js)

(a) 0.413 eV

(b) 0.825 eV

(c) 1.65 eV

(d) 1.32 eV

(ii) The variation of maximum kinetic energy (K_max) of the emitted photoelectrons with frequency (v) of the incident radiations can be represented by

(iii) The variation of photoelectric current (i) with the intensity of the incident radiation (I) can be represented by

(iv) The graph between the stopping potential (V₀) and \(\left(\frac{1}{\lambda}\right)\) is shown in the figure \(\phi_{1}, \phi_{2}, \phi_{3}\) 3 are work function. Which of the following options is correct?

\(\text { (a) } \phi_{1}: \phi_{2}: \phi_{3}=1: 2: 3\)

\(\text { (b) } \phi_{1}: \phi_{2}: \phi_{3}=4: 2: 1\)

\(\text { (c) } \phi_{1}: \phi_{2}: \phi_{3}=1: 2: 4\)

(d) Ultraviolet light can be used to emit photoelectrons from metal 2 and metal 3 only

(v) Which of the following figures represent the variation of particle momentum and the associated de- Broglie wavelength?

5)

When light of sufficiently high frequency is incident on a metallic surface, electrons are emitted from the metallic surface. This phenomenon is called photoelectric emission. Kinetic energy of the emitted photoelectrons depends on the wavelength of incident light and is independent of the intensity of light. Number of emitted photoelectrons depends on intensity. (hv - \(\phi\) is the maximum kinetic energy of emitted photoelectrons (where \(\phi\) is the work function of metallic surface). Reverse effect of photo emission produces X-ray. X-ray is not deflected by electric and magnetic fields. Wavelength of a continuous X-ray depends on potential difference across the tube. Wavelength of characteristic X-ray depends on the atomic number.
(i) Einstein's photoelectric equation is

\(\text { (a) } E_{\max }=h v-\phi\)

\(\text { (b) } E=m c^{2}\)

\(\text { (c) } E^{2}=p^{2} c^{2}+m_{0}^{2} c^{4}\)

\(\text { (d) } E=\frac{1}{2} m v^{2}\)

(ii) Light of wavelength \(\lambda\) which is less than threshold wavelength is incident on a photosensitive material. If incident wavelength is decreased so that emitted photoelectrons are moving with some velocity then stopping potential will

(a) increase

(b) decrease

(c) be zero

(d) become exactly half

(iii) When ultraviolet rays incident on metal plate then photoelectric effect does not occur, it occur by incident of

(a) Infrared rays

(b) X-rays

(c) Radio wave

(d) Micro wave

(iv) If frequency (v > v₀) of incident light becomes n times the initial frequency (v), then K.E. of the emitted photoelectrons becomes (v₀ threshold frequency).

(a) n times of the initial kinetic energy

(b) More than n times of the initial kinetic energy

(c) Less than n times of the initial kinetic energy

(d) Kinetic energy of the emitted photoelectrons remains unchanged

(v) A monochromatic light is used in a photoelectric experiment. The stopping potential

(a) Is related to the mean wavelength	(b) Is related to the shortest wavelength
(c) Is not related to the minimum kinetic energy of emitted photoelectrons	(d) Intensity of incident light

CBSE 12th Standard Physics Subject Wave Optics Chapter Case Study Questions 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
When light from a monochromatic source is incident on a single narrow slit, it gets diffracted and a pattern of alternate bright and dark fringes is obtained on screen, called "Diffraction Pattern" of single slit. In diffraction pattern of single slit, it is found that
(I) Central bright fringe is ·of maximum intensity and the intensity of any secondary bright fringe decreases with increase in its order.
(II) Central bright fringe is twice as wide as any other secondary bright or dark fringe .

(i) A single slit of width 0.1 mm is illuminated by a parallel beam of light of wavelength 6000 A and diffraction bands are observed on a screen 0.5 m from the slit. The distance of the third dark band from the central bright band is

(a) 3 mm (b) 1.5 mm (c) 9 mm (d) 4.5 mm

(ii) In Fraunhofer diffraction pattern, slit width is 0.2 mm and screen is at 2 m away from the lens. If wavelength of light used is 5000 \(\lambda\) then the distance between the first minimum on either side the central maximum is

(a) 10^-1 m (b) 10^-2 m (c) 2 x 10^-2 m (d) 2 x 10^-1m

(iii) Light of wavelength 600 nm is incident normally on a slit of width 0.2 mm. The angular width of central maxima in the diffraction pattern is (measured from minimum to minimum)

(a) 6 x 10^-3 rad (b) 4 x 10^-3 rad (c) 2.4 x 10^-3 rad (d) 4.5 x 10^-3 rad

(iv) A diffraction pattern is obtained by using a beam of red light. What will happen, if the red light is replaced by the blue light?

(a) bands disappear

(b) bands become broader and farther apart

(c) no change will take place

(d) diffraction bands become narrower and crowded together.

(v) To observe diffraction, the size of the obstacle

(a) should be A/2, where A is the wavelength. (b) should be of the order of wavelength.

(c) has no relation to wavelength. (d) should be much larger than the wavelength.
2)
A narrow tube is bent in the form of a circle of radius R, as shown in figure. Two small holes S and D are made in the tube at the positions at right angle to each other. A source placed at S generates a wave of intensity Io which is equally divided into two parts: one part travels along the longer path, while the other travels along the shorter path. Both the waves meet at point D where a detector is placed.

(i) If a maxima is formed at a detector, then the magnitude of wavelength \(\lambda\) of the wave produced is given by

\((a) \pi R\) \((b) \frac{\pi R}{2}\) \((c) \frac{\pi R}{4}\) (d) all of these

(ii) If the intensity ratio of two coherent sources used in Young's double slit experiment is 49 : 1, then the ratio between the maximum and minimum intensities in the interference pattern is

(a) 1: 9 (b) 9: 16 (c) 25: 16 (d) 16: 9

(iii) The maximum intensity produced at D is given by

(a) 4I₀ (b) 2I₀ (c) I₀ (d) 3I₀

(iv) In a Young's double slit experiment, the intensity at a point where the path difference is \(\lambda\)/6 (\(\lambda\) - wavelength of the light) is I. If I₀ denotes the maximum intensity, then I/I₀ is equal to

\((a) \frac{1}{2}\) \((b) \frac{\sqrt{3}}{2}\) \((c) \frac{1}{\sqrt{2}}\) \((d) \frac{3}{4}\)

(v) Two identical light waves, propagating in the same direction, have a phase difference d. After they superpose the intensity of the resulting wave will be proportional to

\((a) \cos \delta\) \((b) \cos (\delta / 2)\) \((c) \cos ^{2}(\delta / 2)\) \((d) \cos ^{2} \delta\)

3)

Wavefront is a locus of points which vibratic in same phase. A ray of light is perpendicular to the wavefront. According to Huygens principle, each point of the wavefront is the source of a secondary disturbance and the wavelets connecting from these points spread out in all directions with the speed of wave. The figure shows a surface XY separating two transparent media, medium-1 and medium-2. The lines ab and cd represent wavefronts of a light wave travelling in medium- 1 and incident on XY. The lines ef and gh represent wavefronts of the light wave in medium -2 after refraction.

(i) Light travels as a

(a) parallel beam in each medium	(b) convergent beam in each medium
(c) divergent beam in each medium	(d) divergent beam in one medium and convergent beam in the other medium.

(ii) The phases of the light wave at c, d, e and f are \(\phi_{c}, \phi_{d}, \phi_{e}\) and \( \phi_{f}\) respectively. It is given that \(\phi_{c} \neq \phi_{f}\)

\(\text { (a) } \phi_{c} \text { cannot be equal to } \phi_{d}\)	\(\text { (b) } \phi_{d} \text { can be equal to } \phi_{e}\)
\(\text { (c) }\left(\phi_{d}-\phi_{f}\right) \text { is equal to }\left(\phi_{c}-\phi_{e}\right)\)	\(\text { (d) }\left(\phi_{d}-\phi_{c}\right) \text { is not equal to }\left(\phi_{f}-\phi_{e}\right)\)

(iii) Wavefront is the locus of all points, where the particles of the medium vibrate with the same

(a) phase

(b) amplitude

(c) frequency

(d) period

(iv) A point source that emits waves uniformly in all directions, produces wavefronts that are

(a) spherical

(b) elliptical

(c) cylindrical

(d) planar

(v) What are the types of wavefronts ?

(a) Spherical

(b) Cylindrical

(c) Plane

(d) All of these

4)

Huygen's principle is the basis of wave theory of light. Each point on a wavefront acts as a fresh source of new disturbance, called secondary waves or wavelets. The secondary wavelets spread out in all directions with the speed light in the given medium.An initially parallel cylindrical beam travels in a medium of refractive index \(\mu(I)=\mu_{0}+\mu_{2} I\), where \(\mu_{0} \text { and } \mu_{2}\)are positive constants and I is the intensity of the light beam. The intensity of the beam is decreasing with increasing radius.

(i) The initial shape of the wavefront of the beam is

(a) planar	(b) convex
(c) concave	(d) convex near the axis and concave near the periphery

(ii) According to Huygens Principle, the surface of constant phase is

(a) called an optical ray	(b) called a wave
(c) called a wavefront	(d) always linear in shape

(iii) As the beam enters the medium, it will

(a) travel as a cylindrical beam	(b) diverge
(c) converge	(d) diverge near tile axis and converge near the periphery.

(iv) Two plane wavefronts of ligbt, one incident on a thin convex lens and another on the refracting face of a thin prism. After refraction at them, the emerging wavefronts respectively become

(a) plane wavefront and plane wavefront	(b) plane wavefront and spherical wavefront
(c) spherical wavefront and plane wavefront	(d) spherical wavefront and spherical wavefront

(v) Which of the following phenomena support the wave theory of light?
1. Scattering
2. Interference
3. Diffraction
4. Velocity of light in a denser medium is less than the velocity of light in the rarer medium

(a) 1,2,3

(b) 1,2,4

(c) 2,3,4

(d) 1,3,4

5)
Interference is based on the superposition principle. According to this principle, at a particular point in the medium, the resultant displacement produced by a number of waves is the vector sum of the displacements produced by each of the waves. If two sodium lamps illuminate two pinholes S₁ and S₂. The intensities will add up and no interference fringes will be observed on the screen. Here the source undergoes abrupt phase change in times of the order of 10^-10 seconds.

(i) Two coherent sources of intensity 10 W/m²and 25 W/m² interfere to form fringes. Find the ratio of maximum intensity to minimum intensity

(a) 15.54 (b) 16.78 (c) 19.72 (d) 18.39

(ii) Which of the following does not show interference?

(a) Soap bubble (b) Excessively thin film (c) A thick film (d) Wedge shaped film

(iii) In a Young's double-slit experiment, the slit separation is doubled. To maintain the same fringe spacing on the screen, the screen-to-slit distance D must be changed to

(a) 2D (b) 4D (c) D/2 (d) D/4

(iv) The maximum number of possible interference maxima for slit separation equal to twice the wavelength in Young's double-slit experiment, is

(a) infinite (b) five (c) three (d) zero

(v) The resultant amplitude of a vibrating particle by the superposition of the two waves \(y_{1}=a \sin \left[\omega t+\frac{\pi}{3}\right] \text { and } y_{2}=a \sin \omega t \text { is }\)

(a) a (b)\(\sqrt{2}\) a (c) 2a (d) \(\sqrt{3}\) a

CBSE 12th Standard Physics Subject Ray Optics and Optical Instruments Chapter Case Study Questions 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
A convex or converging lens is thicker at the centre than at the edges. It converges a parallel beam of light on refraction through it. It has a real focus. Convex lens is of three types:
(i) Double convex lens
(ii) Plano-convex lens
(iii) Concavo-convex lens. Concave lens is thinner at the centre than at the edges. It diverges a parallel beam of light on refraction through it. It has a virtual focus.
(i) A point object 0 is placed at a distance of 0.3 m from a convex lens (focal length 0.2 m) cut into two halves each of which is displaced by 0.0005 m as shown in figure.What will be the location of the image?

(a) 30 cm right of lens (b) 60 ern right of lens

(c) 70 ern left of lens (d) 40 cm left oflens

(ii) Two thin lenses are in contact and the focal length of the combination is 80 cm. If the focal length of one lens is 20 cm, the focal length of the other would be

(a) -26.7 cm (b) 60 crn

(c) 80 cm (d) 20 cm

(iii) A spherical air bubble is embedded in a piece of glass. For a ray of light passing through the bubble, it behaves like a

(a) converging lens (b) diverging lens

(c) plano-converging lens (d) plano-diverging lens

(iv) Lens used in magnifying glass is

(a) Concave lens (b) Convex lens (c) Both (a) and (b) (d) None of the above

(v) The magnification of an image by a convex lens is positive only when the object is placed

(a) at its focus F (b) between F and 2F

(c) at 2F (d) between F and optical centre
2)
Refraction of light is the change in the path oflight as it passes obliquely from one transparent medium to another medium. According to law of refraction \(\frac{\sin i}{\sin r}={ }^{1} \mu_{2}\) where \({ }^{1} \mu_{2}\) is called refractive index of second medium with respect to first medium. From refraction at a convex spherical surface, we have \(\frac{\mu_{2}}{v}-\frac{\mu_{1}}{u}=\frac{\mu_{2}-\mu_{1}}{R}\) Similarly from refraction at a concave spherical surface when object lies in the rarer medium, we have \(\frac{\mu_{2}}{v}-\frac{\mu_{1}}{u}=\frac{\mu_{2}-\mu_{1}}{R}\) and when object lies in the denser medium, we have \(\frac{\mu_{1}}{v}-\frac{\mu_{2}}{u}=\frac{\mu_{1}-\mu_{2}}{R}\).
(i) Refractive index of a medium depends upon

(a) nature of the medium (b) wavelength of the light used

(c) temperature (d) all of these

(ii) A ray of light of frequency 5 x 10¹⁴Hz is passed through a liquid. The wavelength of light measured inside the liquid is found to be 450 x 10^-9 m. The refractive index of the liquid is

(a) 1.33 (b) 2.52 (c) 2.22 (d) 0.75

(iii) A ray of light is incident at an angle of 60° on one face of a rectangular glass slab of refractive index 1.5. The angle of refraction is

(a) sin^-1(0.95) (b) sin^-1(0.58) (c) sin^-1(0.79) (d) sin^-1(0.86)

(iv) A point object is placed at the centre of a glass sphere of radius 6 cm and refractive index 1.5. The distance of the virtual image from the surface of sphere is

(a) 2 cm (b) 4 cm (c) 6 cm (d) 12 cm

(v) In refraction, light waves are bent on passing from one medium to the second medium because in the second medium

(a) the frequency is different (b) the co-efficient of elasticity is different

(c) the speed is different (d) the amplitude is smaller.

3)

The lens maker's formula relates the focal length of a lens to the refractive index of the lens material and the radii of curvature of its two surfaces. This formula is called so because it is used by manufacturers to design lenses of
required focal length from a glass of given refractive index. If the object is placed at infinity, the image will be formed at focus for both double convex lens and double concave lens
Therefore, lens maker's formula is \(\frac{1}{f}=\left[\frac{\mu_{2}-\mu_{1}}{\mu_{1}}\right]\left[\frac{1}{R_{1}}-\frac{1}{R_{2}}\right]\)
When lens is placed in air, \(\mu\)₁= 1 and \(\mu\)₂ = \(\mu\). The lens maker formula takes the form \(\frac{1}{f}=(\mu-1)\left[\frac{1}{R_{1}}-\frac{1}{R_{2}}\right]\)
(i) The radius of curvature of each face of biconcave lens with refractive index 1.5 is 30 cm. The focal length of the lens in air is

(a) 12 cm

(b) 10 cm

(c) 20 cm

(d) 30 cm

(ii) The radii of curvature of the faces of a double convex lens are 10 cm and 1.5 cm. If focal length is 12 cm, then refractive index of glass is

(a) 1.5

(b) 1.78

(c) 2.0

(d) 2.52

(iii) An under-water swimmer cannot see very clearly even in absolutely clear water because of

(a) absorption oflight in water	(b) scattering of light in water
(c) reduction of speed of light in water	(d) change in the focal length of eye-lens

(iv) A thin lens of glass (\(\mu\) = 1.5) offocallength 10 cm is immersed in water (\(\mu\) = 1.33). The new focal length is

(a) 20 cm

(b) 40 cm

(c) 48 cm

(d) 12 cm

(v) An object is immersed in a fluid. In order that the object becomes invisible, it should

(a) behave as a perfect reflector

(b) absorb all light falling on it

(c) have refractive index one

(d) have refractive index exactly matching with that of the surrounding fluid.

4)
A prism is a portion of a transparent medium bounded by two plane faces inclined to each other at a suitable angle. A ray of light suffers two refractions on passing through a prism and hence deviates through a certain angle from its original path. The angle of deviation of a prism is, \(\delta\) = (\(\mu\)- 1) A, through which a ray deviates on passing through a thin prism of small refracting angle A.
If \(\mu\) is refractive index of the material of the prism, then prism formula is,\(\mu=\frac{\sin \left(A+\delta_{m}\right) / 2}{\sin A / 2}\)
(i) For which colour, angle of deviation is minimum?

(a) Red (b) Yellow (c) Violet (d) Blue

(ii) When white light moves through vacuum

(a) all colours have same speed (b) different colours have different speeds

(c) violet has more speed than red (d) red has more speed than violet.

(iii) The deviation through a prism is maximum when angle of incidence is

(a) 45° (b) 70° (c) 90° (d) 60°

(iv) What is the deviation produced by a prism of angle 6°? (Refractive index of the material of the prism is 1.644).

(a) 3.864° (b): 4.595° (c) 7.259° (d) 1.252°

(v) A ray of light falling at an angle of 50° is refracted through a prism and suffers minimum deviation. If the angle of prism is 60°, then the angle of minimum deviation is

(a) 45° (b) 75° (c) 50° (d) 40°

5)

An optical fibre is a thin tube of transparent material that allows light to pass through, without being refracted into the air or another external medium. It make use of total internal reflection. These fibres are fabricated in such a way that light reflected at one side of the inner surface strikes the other at an angle larger than critical angle. Even, if fibre is bent, light can easily travel along the length.

(i) Which of the following is based on the phenomenon of total internal reflection of light?

(a) Sparkling of diamond	(c) Instrument used by doctors for endoscopy
(b) Optical fibre communication	(d) All of these

(ii) A ray of light will undergo rotal internal reflection inside the optical fibre, if it

(a) goes from rarer medium to denser medium

(b) is incident at an angle less than the critical angle

(c) strikes the interface normally

(d) is incident at an angle greater than the critical angle

(iii) If in core, angle of incidence is equal to critical angle, then angle of refraction will be

(a) 0°

(b) 45°

(c) 90

(d) 180°

(iv) In an optical fibre (shown), correct relation for refractive indices of core and cladding is

(a) n₁ = n₂

(b) n₁ > n₂

(c) n₁ < n₂

(d) n₁ + n₂ = 2

(v) If the value of critical angle is 30° for total internal reflection from given optical fibre, then speed of light in that fibre is

(a) 3 x 108 m S^-1

(b) 1.5 x 108 m S^-1

(c) 6 x 108 m s^-1

(d) 4.5 x 108 m s^-1

CBSE 12th Standard Physics Subject Alternating Current Chapter Case Study Questions 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
When a pure resistance R, pure inductor L and an ideal capacitor of capacitance C is connected in series to a source of alternating e.m.f., then current at any instant through the three elements has the same amplitude and is represented as I = I_osinwt. However, voltage across each element has a different phase relationship with the current as shown in graph.
The effective resistance of RLC circuit is called impedance (2) of the circuit and the voltage leads the current by a phase angle \(\phi .\)

A resistor of \(12 \Omega\) a capacitor of reactance \(14 \Omega\) and a pure inductor of inductance 0.1 H are joined in series and placed across 200 V, 50 Hz a.c. supply
(i) The value of inductive reactance is

\(\text { (a) } 15 \Omega\) \(\text { (b) } 31.4 \Omega\) \(\text { (c) } 20 \Omega\) \(\text { (d) } 30 \Omega\)

(ii) The value of impedance is

\(\text { (a) } 20 \Omega\) \(\text { (b) } 15 \Omega\) \(\text { (c) } 30 \Omega\) \(\text { (d) } 21.13 \Omega\)

(iii) What is the value of current in the circuit?

(a) 5 A (b) 15 A (c) 10 A (d) 9.46 A

(iv) What is the value of the phase angle between current and voltage?

\(\text { (a) } 53^{\circ} 9^{\prime}\) \(\text { (b) } 63^{\circ} 9^{\prime}\) \(\text { (c) } 55^{\circ} 4^{\prime}\) (d) 50°

(v) From graph, which one is true from following?

\(\text { (a) } V_{L} \geq V_{C}\) \(\text { (b) } V_{L}<V_{C}\) \(\text { (c) } V_{L}>V_{C}\) \(\text { (d) } V_{L}=V_{C}\)
2)
A transformer is essentially an a.c. device. It cannot work on d.c. It changes alternating voltages or currents. It does not affect the frequency of a.c. It is based on the phenomenon of mutual induction. A transformer essentially consists of two coils of insulated copper wire having different number of turns and wound on the same soft iron core.
The number of turns in the primary and secondary coils of an ideal transformer are 2000 and 50 respectively. The primary coil is connected to a main supply of 120 V and secondary coil is connected to a bulb of resistance \(0.6 \Omega\)
(i) The value of voltage across the secondary coil is

(a) 5V (b) 2V (c) 3 V (d) 10 V

(ii) The value of current in the bulb is

(a) 7 A (b) 15 A (c) 3 A (d) 5 A

(iii) The value of current in primary coil is

(a) 0.125 A (b) 2.52 A (c) 1.51 A (d) 3.52 A

(iv) Power in primary coil is

(a) 20W (b) 5W (c) 10 W (d) 15W

(v) Power in secondary coil is

(a) 15W (b) 20 W (c) 7W (d) 8 W

3)

An LC circuit also called a resonant circuit, tank circuit or tuned circuit is an electric circuit consisting of an inductor represented by the letter L and a capacitor, represented by the letter C connected together. An LC circuit is an idealized model since it assumes there is no dissipation of energy due to resistance.
An LC circuit contains a 20 mH inductor and a \(50 \mu \mathrm{F}\) capacitor with an initial charge of 10 mC The resistance of the circuit is negligible. Let the instant the circuit is closed be t = 0.

(i) The total energy stored initially is

(a) 5 J

(b) 3 J

(c) 10 J

(d) 1 J

(ii) The natural frequency of the circuit is

(a) 159.24 Hz

(b) 200.12 Hz

(c) 110.25 Hz

(d) 95 Hz

(iii) At what time is the energy stored completely electrical?

\(\text { (a) } T, 5 T, 9 T\)

\(\text { (b) } \frac{T}{2}, \frac{5 T}{2}, \frac{9 T}{2}\)

(c) 0, T, 2T, 3T

\(\text { (d) } 0, \frac{T}{2}, T, \frac{3 T}{2}\)

(iv) At what time is the energy stored completely magnetic?

\(\text { (a) } \frac{T}{2}, \frac{3 T}{2}, \frac{T}{4}\)

\(\text { (b) } \frac{T}{3}, \frac{T}{9}, \frac{T}{12}\)

(c) 0, 2T, 3T

\(\text { (d) } \frac{T}{4}, \frac{3 T}{4}, \frac{5 T}{4}\)

(v) The value of X_L is

\(\text { (a) } 20 \Omega\)

\(\text { (b) } 40 \Omega\)

\(\text { (c) } 60 \Omega\)

\(\text { (d) } 50 \Omega\)

4)
Step-down transformers are used to decrease or step-down voltages. These are used when voltages need to be lowered for use in homes and factories.
A small town with a demand of 800 kW of electric power at 220 V is situated 15 km away from an electric plant generating power at 440 V. The resistance of the two wire line carrying power is \(0.5 \Omega\) per km. The town gets power from the line through a 4000 - 220 V step-down transformer at a sub-station in the town.

(i) The value of total resistance of the wires is

\(\text { (a) } 25 \Omega\) \(\text { (b) } 30 \Omega\) \(\text { (c) } 35 \Omega\) \(\text { (d) } 15 \Omega\)

(ii) The line power loss in the form of heat is

(a) 550 kW (b) 650 kW (c) 600 kW (d) 700 kW

(iii) How much power must the plant supply, assuming there is negligible power loss due to leakage?

(a) 600 kW (b) 1600 kW (c) 500 W (d) 1400 kW

(iv) The voltage drop in the power line is

(a) 1700V (b) 3000V (c) 2000V (d) 2800 V

(v) The total value of voltage transmitted from the plant is

(a) 500 V (b) 4000 V (c) 3000 V (d) 7000 V

5)

A transformer is an electrical device which is used for changing the a.c. voltages. It is based on the phenomenon of mutual induction i.e. whenever the amount of magnetic flux linked with a coil changes, an e.m.f is induced in the neighbouring coil. For. an ideal transformer, the resistances of the primary and secondary windings are negligible.

It can be shown that \(\frac{E_{s}}{E_{p}}=\frac{I_{p}}{I_{s}}=\frac{n_{s}}{n_{p}}=k\)
where the symbols have their standard meanings.
For a step up transformer \(n_{s}>n_{p} ; E_{s}>E_{p} ; k>1 ; \quad \therefore I_{s}
For a step down transformer \(n_{s}
The above relations are on the assumptions that efficiency of transformer is 100%.
lentlac ,effciency \(\eta=\frac{\text { output power }}{\text { intput power }}=\frac{E_{s} I_{s}}{E_{p} I_{p}}\)
(i) Which of the following quantity remains constant in an ideal transformer?

(a) Current

(b) Voltage

(c) Power

(d) All of these

(ii) Transformer is used to

(a) convert ac to dc voltage	(b) convert de to ac voltage
(c) obtain desired dc power	(d) obtain desired ac voltage and current

(iii) The number of turns in primary coil of a transformer is 20 and the number of turns in a secondary is 10. If the voltage across the primary is 220 ac V, what is the voltage across the secondary?

(a) 100 ac V

(b) 120 ac V

(c) 110 ac V

(d) 220 ac V

(iv) In a transformer the number of primary turns is four times that of the secondary turns. Its primary is connected to an a.c. source of voltage V. Then

(a) current through its secondary is about four times that of the current through its primary

(b) voltage across its secondary is about four times that of the voltage across its primary.

(c) voltage across its secondary is about two times that of the voltage across its primary

(d) voltage across its secondary is about \(\frac{1}{2 \sqrt{2}}\) times that of the voltage across its primary

(v) A transformer is used to light 100 W-110 V lamp from 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is

(a) 95%

(b) 99%

(c) 90%

(d) 96%

CBSE 12th Standard Physics Subject Moving Charges And Magnetism Chapter Case Study Questions 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)

Various methods can be used to measure the mass of an atom. One possibility is through the use of a mass spectrometer. The basic feature of a Banbridge mass spectrometer is illustrated in figure. A particle carrying a charge +q is first sent through a velocity selector and comes out with velocity v = E/B.
The applied electric and magnetic fields satisfy the relation E = vB so that the trajectory of the particle is a straight line. Upon entering a region where a second magnetic field \(\vec{B}_{0}\) pointing into the page has been applied, the particle will move in a circular path with radius r and eventually strike the photographic plate.

(i) In mass spectrometer, the ions are sorted out in which of the following ways?

(a) By accelerating them through electric field

(b) By accelerating them through magnetic field

(c) By accelerating them through electric and magnetic field

(d) By applying a high voltage

(ii) Radius of particle in second magnetic field B_o is

\(\text { (a) } \frac{2 m v}{q E_{0}}\)

\(\text { (b) } \frac{m v}{q E_{0}}\)

\(\text { (c) } \frac{m v}{q B_{0}}\)

\(\text { (d) } \frac{2 m E_{0} v}{q B_{0}}\)

(iii) Which of the following will trace a circular trajectory wit largest radius?

(a) Proton

(b) -\(\alpha\)particle

(c) Electron

(d) A particle with charge twice and mass thrice that of electron

(iv) Mass of the particle in terms q, B_o, B,r and E is

\(\text { (b) } \frac{q B_{0} B r}{E}\)

\(\text { (c) } \frac{q B r}{E B_{0}}\)

\(\text { (d) } \frac{q B r E}{B_{0}}\)

(v) The particle comes out of velocity selector along a straight line, because

(a) electric force is less than magnetic force	(b) electric force is greater than magnetic force
(c) electric and magnetic force balance each other	(d) can't say.

2)
An electron with speed V_o<< c moves in a circle ofradius r_o in a uniform magnetic field. This electron is able to traverse a circular path as magnetic field is perpendicular to the velocity of the electron. A force acts on the particle perpendicular to both \(\vec{v}_{0}\) and \(\vec{B}\). This force continuously deflects the particle sideways without changing its speed and the particle will move along a circle perpendicular to the field. The time required for one revolution of the electron is T_o .

(i) If the speed of the electron is now doubled to 2v_o.The radius of the circle will change to

\(\text { (a) } 4 r_{0}\) \(\text { (b) } 2 r_{0}\) \(\text { (c) } r_{0}\) \(\text { (d) } r_{0} / 2\)

(ii) If v_o = 2v_o then the time required for one revolution of the electron will change to

\(\text { (a) } 4 T_{0}\) \(\text { (b) } 2 T_{0}\) \(\text { (c) } T_{0}\) \(\text { (d) } T_{0} / 2\)

(iii) A charged particles is projected in a magnetic field \(\vec{B}=(2 \hat{i}+4 \hat{j}) \times 10^{2} \mathrm{~T}\) The acceleration of the particle is found to be \(\vec{a}=(x \hat{i}+2 \hat{j}) \mathrm{m} \mathrm{s}^{-2}\). Find the value of x.

(a) 4 m S^-2 (b) -4 m s^-2 (c) -2 m s^-2 (d) 2 m s^-2

(iv) If the given electron has a velocity not perpendicular to B, then trajectory of the electron is

(a) straight line (b) circular (c) helical (d) zig-zag

(v) If this electron of charge (e) is moving parallel to uniform magnetic field with constant velocity v, the force acting on the electron is

(a) Bev \(\text { (b) } \frac{B e}{v}\) \(\text { (c) } \frac{B}{e v}\) (d) zero

3)

Moving coil galvanometer operates on Permanent Magnet Moving Coil (PMMC) mechanism and was designed by the scientist D'arsonval.
Moving coil galvanometers are of two types
(i) Suspended coil
(ii) Pivoted coil type or tangent galvanometer.
Its working is based on the fact that when a current carrying coil is placed in a magnetic field, it experiences a torque. This torque tends to rotate the coil about its axis of suspension in such a way that the magnetic flux passing through the coil is maximum.

(i) A moving coil galvanometer is an instrument which

(a) is used to measure emf

(b) is used to measure potential difference

(c) is used to measure resistance

(d) is a deflection instrument which gives a deflection when a current flows through its coil

(ii) To make the field radial in a moving coil galvanometer

(a) number of turns of coil is kept small	(b) magnet is taken in the form of horse-shoe
(c) poles are of very strong magnets	(d) poles are cylindrically cut

(iii) The deflection in a moving coil galvanometer is

(a) directly proportional to torsional constant of spring

(b) directly proportional to the number of turns in the coil

(c) inversely proportional to the area of the coil

(d) inversely proportional to the current in the coil

(iv) In a moving coil galvanometer, having a coil of N-turns of area A and carrying current I is placed in a radial field of strength B.
The torque acting on the coil is

\(\text { (a) } N A^{2} B^{2} I\)

\(\text { (b) } N A B I^{2}\)

\(\text { (c) } N^{2} A B I\)

(d) NABI

(v) To increase the current sensitivity of a moving coil galvanometer, we should decrease

(a) strength of magnet	(b) torsional constant of spring
(c) number ofturns in coil	(d) area of coil

4)

A galvanometer can be converted into voltmeter of given range by connecting a suitable resistance R_s in series with the galvanometer, whose value is given by
\(R_{s}=\frac{V}{I_{g}}-G\)
where V is the voltage to be measured, I_g is the current for full scale deflection of galvanometer and G is the resistance of galvanometer

Series resistort (R_s) increases range of voltmeter and the effective resistance of galvanometer. It also protects the galvanometer from damage due to large current.
Voltmeter is a high resistance instrument and it is always connected in parallel with the circuit element across which potential difference is to be measured. An ideal voltmeter has infinite resistance
In order to increase the range of voltmeter n times the value of resistance to be connected in series with galvanometer is R_s = (n - l)G.
(I) 10 mA current can pass through a galvanometer of resistance \(25 \Omega\) What resistance in series should be connected through it, so that it is converted into a voltmeter of 100 V?

\(\text { (a) } 0.975 \Omega\)

\(\text { (b) } 99.75 \Omega\)

\(\text { (c) } 975 \Omega\)

\(\text { (d) } 9975 \Omega \text { . }\)

(ii) There are 3 voltmeter A, B, C having the same range but their resistance are \(15,000 \Omega, 10,000 \Omega\) and \(5,000 \Omega\) respectively. The best voltmeter amongst them is the one whose resistance is

\(\text { (a) } 5000 \Omega\)

\(\text { (b) } 10,000 \Omega\)

\(\text { (c) } 15,000 \Omega\)

(d) all are equally good

(iii) A milliammeter of range 0 to 25 mA and resistance of \(10 \Omega\) is to be converted into a voltmeter with a range of 0 to 25 V. The resistance that should be connected in series will be

(a) \(930 \Omega\)

\(\text { (b) } 960 \Omega\)

\(\text { (c) } 990 \Omega\)

\(\text { (d) } 1010 \Omega\)

(iv) To convert a moving coil galvanometer (MCG) into a voltmeter

(a) a high resistance R is connected in parallel with MCG

(b) a low resistance R is connected in parallel with MCG

(c) a low resistance R is connected in series with MCG

(d) a high resistance R is connected in series with MCG

(v) The resistance of an ideal voltmeter is

(a) zero

(b) low

(c) high

(d) infinity

5)

A charged particle moving in a magnetic field experiences a force that is proportional to the strength of the magnetic field, the component of the velocity that is perpendicular to the magnetic field and the charge of the particle.
This force is given by \(\vec{F}=q(\vec{v} \times \vec{B})\) where q is the electric charge of the particle, v is the instantaneous velocity of the particle, and B is the magnetic field (in tesla).
The direction of force is determined by the rules of cross product of two vectors
Force is perpendicular to both velocity and magnetic field. Its direction is same as \(\vec{v} \times \vec{B}\) if q is positive and opposite of \(\vec{v} \times \vec{B}\) if q is negative
The force is always perpendicular to both the velocity of the particle and the magnetic field that created it. Because the magnetic force is always perpendicular to the motion, the magnetic field can do no work on an isolated charge. It can only do work indirectly, via the electric field generated by a changing magnetic field.

(I) When a magnetic field is applied on a stationary electron, it

(a) remains stationary

(b) spins about its own axis

(c) moves in the direction of the field

(d) moves perpendicular to the direction of the field.

(ii) A proton is projected with a uniform velocity v along the axis of a current carrying solenoid, then

(a) the proton will be accelerated along the axis

(b) the proton path will be circular about the axis

(c) the proton moves along helical path

(d) the proton will continue to move with velocity v along the axis.

(iii) A charged particle experiences magnetic force in the presence of magnetic field. Which of the following statement is correct?

(a) The particle is stationary and magnetic field is perpendicular.

(b) The particle is moving and magnetic field is perpendicular to the velocity

(c) The particle is stationary and magnetic field is parallel

(d) The particle is moving and magnetic field is parallel to velocity

(iv) A charge q moves with a velocity 2 ms^-1 along x-axis in a uniform magnetic field \(\vec{B}=(\hat{i}+2 \hat{j}+3 \hat{k}) \mathrm{T}\) then charge will experience a force

(a) in z-y plane

(b) along -yaxis

(c) along +z axis

(d) along -z axis

(v) Moving charge will produce

(a) electric field only	(b) magnetic field only
(c) both electric and magnetic field	(d) none ofthese.

CBSE 12th Standard Physics Subject Current Electricity Chapter Case Study Questions 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
The flow of charge in a particular direction constitutes the electric current. Current is measured in Ampere. Quantitatively, electric current in a conductor across an area held perpendicular to the direction of flow of charge is defined as the amount of charge is flowing across that area per unit time.
Current density at a point in a conductor is the ratio of the current at that point in the conductor to the area of cross section of the conductor of that point.
The given figure shows a steady current flows in a metallic conductor of non uniform cross section. Current density depends inversely on area, so, here \(J_{1}>J_{2}, \text { as } A_{1}.

(i) What is the current flowing through a conductor, if one million electrons are crossing in one millisecond through a cross-section of it ?

(a) 2.5 x 10^-10 A (b) 1.6 x 10^-10 A

(c) 7.5 X 10^-9 A (d) 8.2 x 10^-11 A

(ii) SI unit of electric current is

(a) Cs (b) Ns^-2 (c) Cs^-1 C^-1s^-1

(iii) A steady current flows in a metallic conductor of non-uniform cross-section. Which of these quantities is constant along the conductor?

(a) Electric field (b) Drift velocity (c) Current (d) Current density

(iv) A constant current I is flowing along the length of a conductor of variable cross-section as shown in the figure. The quantity which does not depend upon the area of cross-section is

(a) electron density (b) current density

(c) drift velocity (d) electric field

(v) When a current of 40 A flows through a conductor of area 10 m², then the current density is

(a) 4 A/m² (b) 1 A/m² (c) 2 A/m² (d) 8 A/m²

2)

According to Ohm's law, the current flowing through a conductor is directly proportional to the potential difference across the ends of the conductor i.e \(I \propto V \Rightarrow \frac{V}{I}=R\) where R is resistance of the conductor Electrical resistance of a conductor is the obstruction posed by the conductor to the flow of electric current through it. It depends upon length, area of cross-section, nature of material and temperature of the conductor We can write \(R \propto \frac{l}{A} \text { or } R=\rho \frac{l}{A}\) where \(\rho\) is electrical resistivity of the material of the conductor.
(i) Dimensions of electric resistance is

\(\text { (a) }\left[\mathrm{ML}^{2} \mathrm{~T}^{-2} \mathrm{~A}^{-2}\right]\)

\(\text { (b) }\left[M L^{2} T^{-3} A^{-2}\right]\)

\(\text { (c) }\left[\mathrm{M}^{-1} \mathrm{~L}^{-2} \mathrm{~T}^{-1} \mathrm{~A}\right]\)

\(\text { (d) }\left[M^{-1} L^{2} T^{2} A^{-1}\right]\)

(ii) If \(1 \mu \mathrm{A}\) current flows through a conductor when potential difference of2 volt is applied across its ends, then the resistance of the conductor is

\(\text { (a) } 2 \times 10^{6} \Omega\)

\(\text { (b) } 3 \times 10^{5} \Omega\)

\(\text { (c) } 1.5 \times 10^{5} \Omega\)

\(\text { (d) } 5 \times 10^{7} \Omega\)

(iii) Specific resistance of a wire depends upon

(a) length

(b) cross-sectional area

(c) mass

(d) none of these

(iv) The slope of the graph between potential difference and current through a conductor is

(a) a straight line	(b) curve
(c) first curve then straight line	(d) first straight line then curve

(v) The resistivity of the material of a wire 1.0 m long, 0.4 mm in diameter and having a resistance of 2.0 ohm is

\(\text { (a) } 1.57 \times 10^{-6} \Omega \mathrm{m}\)

\(\text { (b) } 5.25 \times 10^{-7} \Omega \mathrm{m}\)

\(\text { (c) } 7.12 \times 10^{-5} \Omega \mathrm{m}\)

\(\text { (d) } 2.55 \times 10^{-7} \Omega \mathrm{m}\)

3)

Emf of a cell is the maximum potential difference between two electrodes of the cell when no current is drawn from the cell. Internal resistance is the resistance offered by the electrolyte of a cell when the electric current flows through it. The internal resistance of a cell depends upon the following factors;
(i) distance between the electrodes
(ii) nature and temperature of the electrolyte
(iii) nature of electrodes
(iv) area of electrodes.

For a freshly prepared cell, the value of internal resistance is generally low and goes on increasing as the cell is put to more and more use. The potential difference between the two electrodes of a cell in a closed circuit is called terminal potential difference and its value is always less than the emf of the cell in a closed circuit. It can be written as V = E - Jr.
(i) The terminal potential difference of two electrodes of a cell is equal to emf of the cell when

\(\text { (a) } I \neq 0\)

(b) I=0

(c) both (a) and (b)

(d) neither (a)nor (b)

(ii) A cell of emf E and internal resistance r gives a current of 0.5 A with an external resistance of \(12 \Omega\) and a current of 0.25 A with an external resistance of \(25 \Omega\) .What is the value of internal resistance of the cell?

\(\text { (a) } 5 \Omega\)

\(\text { (b) } 1 \Omega\)

\(\text { (c) } 7 \Omega\)

\(\text { (d) } 3 \Omega\)

(iii) Choose the wrong statement.

(a) Potential difference across the terminals of a cell in a closed circuit is always less than its emf.

(b) Internal resistance of a cell decrease with the decrease in temperature of the electrolyte.

(c) Potential difference versus current graph for a cell is a straight line with a -ve slope

(d) Terminal potential difference of the cell when it is being charged is given as V = E + Ir.

(iv) An external resistance R is connected to a cell of internal resistance r, the maximum current flows in the external resistance, when

(a) R = r

(b) R < r

(c) R> r

(d) R=l/r

(v) IF external resistance connected to a cell has been increased to 5 times, the potential difference across the terminals of the cell increases from 10 V to 30 V. Then, the emf of the cell is

(a) 30 V

(b) 60V

(c) 50 V

(d) 40 V

4)
A single cell provides a feeble current. In order to get a higher current in a circuit, we often use a combination of cells A combination of cells is called a battery, Cells can be joined in series, parallel or in a mixed way.
Two cells are said to be connected in series when negative terminal of one cell is connected to positive terminal of the other cell and so on. Two cells are said to be connected in parallel if positive terminal of each cell is connected to one point and negative terminal of each cell connected to the other point. In mixed grouping of cells, a certains number of identical cells are joined in series, and all such rows are then connected in parallel with each other.

(i) To draw the maximum current from a combination of cells, how should the cells be grouped?

(a) Parallel (b) Series (c) Mixed grouping (d) Depends upon the relative values of internal and external resistances

(ii) The total emf of the cells when n identical cells each of emf e are connected in parallel is

\(\text { (a) } n \varepsilon\) \(\text { (b) } n^{2} \varepsilon\) (c) E \(\text { d) } \frac{\varepsilon}{n}\)

(iii) 4 cells each of emf 2 V and internal resistance of \(1 \Omega\) are connected in parallel to a load resistor of \(2 \Omega\). Then the current through the load resistor is

(a) 2 A (b) 1.5 A (c) 1 A (d) 0.888 A

(iv) If two cells out of n number of cells each of internal resistance 'r' are wrongly connected in series, then total resistance of the cell is

(a) 2nr (b) nr - 4r (c) nr (d) r

(v) Two identical non-ideal batteries are connected in parallel. Consider the following statements.
(i). The equivalent emf is smaller than either of the two emfs.
(ii) The equivalent internal resistance is smaller than either of the two internal resistances

(a) Both (i) and (ii) are correct. (b) (i) is correct but (ii) is wrong

(c) (ii) is correct but (i) is wrong. (d) Both (i) and (ii) are wrong.

5)

Potentiometer is an apparatus used for measuring the emf of a cell or potential difference between two points in an electrical circuit accurately. It is also used to determine the internal resistance of a primary cell. The potentiometer is based on the principle that, if V is the potential difference across any portion of the wire of length 1 and resistance R, then \(V \propto l \text { or } V=k l\) where k is the potential gradient. Thus, potential difference across any portion of potentiometer wire is directly proportional to length of the wire of that portion. The potentiometer wire must be uniform. The resistance of potentiometer wire should be high.

(i) Which one of the following is true about potentiometer?

(a) Its sensitivity is low

(b) It measures the emf of a cell very accurately

(c) It is based on deflection method

(d) None of the above

(ii) A current of 1.0 mA is flowing through a potentiometer wire of length 4 cm and of resistance \(4 \Omega\) .The potential gradient of the potentiometer wire is

\(\text { (a) } 10^{-3} \mathrm{Vm}^{-1}\)

\(\text { (b) } 10^{-5} \mathrm{Vm}^{-2}\)

\(\text { (c) } 2 \times 10^{-3} \mathrm{Vm}^{-1}\)

\(\text { (d) } 4 \times 10^{-3} \mathrm{Vm}^{-1}\)

(iii) Sensitivity of a potentiometer can be increased by

(a) decreasing potential gradient along the wire	(b) increasing potential gradient along the wire
(c) decreasing current through the wire	(d) increasing current through the wire

(iv) A potentiometer is an accurate and versatile device to make electrical measurements of EMF because the method involves

(a) potential gradients

(b) a condition of no current flow through the galvanometer

(c) a combination of cells, galvanometer and resistances

(d) cells

(v) In a potentiometer experiment, the balancing length is 8 m, when the two cells E_land E₂ are joined in series. When the two cells are connected in opposition the balancing length is 4 m. The ratio of the e. m. f. of two cells (E_l/E₂) is

(a) 1: 2

(b) 2: 1

(c) 1: 3

(d) 3: 1

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Chapter Case Study Questions 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)

The potential at any observation point P of a static electric field is defined as the work done by the external agent (or negative of work done by electrostatic field) in slowly bringing a unit positive point charge from infinity to the observation point. Figure shows the potential variation along the line of charges. Two point charges Q₁ and Q₂ lie along a line at a distance from each other.

(i) At which of the points 1, 2 and 3 is the electric field is zero?

(a) 1

(b) 2

(c) 3

(d) Both (a) and (b)

(ii) The signs of charges Q₁ and Q₂respectively are

(a) positive and negative	(b) negative and positive
(c) positive and positive	(d) negative and negative

(iii) Which of the two charges Q₁and Q₂is greater in magnitude?

(a) Q₂

(b) Q₁

(c) Same

(d) Can't determined

(iv) Which of the following statement is not true?

(a) Electrostatic force is a conservative force

(b) Potential energy of charge q at a point is the work done per unit charge in bringing a charge from any point to infinity

(c) When two like charges lie infinite distance apart, their potential energy is zero.

(d) Both (a) and (c).

(v) Positive and negative point charges of equal magnitude are kept at \(\left(0,0, \frac{a}{2}\right)\) and \(\left(0,0, \frac{-a}{2}\right)\) respectively.
The work done by the electric field when another positive point charge is moved from (-a, 0, 0) to (0, a, 0) is

(a) positive

(b) negative

(c) zero

(d) depends on the path connecting the initial and final positions

2)

For the various charge systems, we represent equipotential surfaces by curves and line of force by full line curves. Between any two adjacent equipotential surfaces, we assume a constant potential difference the equipotential surfaces of a single point charge are concentric spherical shells with their centres at the point charge. As the lines of force point radially outwards, so they are perpendicular to the equipotential surfaces at all points.

(i) Identify the wrong statement.

(a) Equipotential surface due to a single point charge is spherical.

(b) Equipotential surface can be constructed for dipoles too.

(c) The electric field is normal to the equipotential surface through the point.

(d) The work done to move a test charge on the equipotential surface is positive

(ii) Nature of equipotential surface for a point charge is

(a) Ellipsoid with charge at foci	(b) Sphere with charge at the centre of the sphere
(c) Sphere with charge on the surface of the sphere	(d) Plane with charge on the surface

(iii) A spherical equipotential surface is not possible

(a) inside a uniformly charged sphere	(b) for a dipole
(c) inside a spherical condenser	(d) for a point charge

(iv) The work done in carrying a charge q once round a circle of radius a with a charge Q at its centre is

\(\text { (a) } \frac{q Q}{4 \pi \varepsilon_{0} a}\)

\(\text { (b) } \frac{q Q}{4 \pi \varepsilon_{0} a^{2}}\)

\(\text { (c) } \frac{q}{4 \pi \varepsilon_{0} a}\)

(d) zero

(v) The work done to move a unit charge along an equipotential surface from P to Q

(a) must be defined as \(-\int_{P}^{Q} \vec{E} \cdot d \vec{l}\)	(b) is zero
(c) can have a non-zero value	(d) both (a) and (b) are correct

3)

The electrical capacitance of a conductor is the measure of its ability to hold electric charge. An isolated spherical conductor of radius R. The charge Q is uniformly distributed over its entire surface. It can be assumed to be concentrated at the centre of the sphere. The potential atany point on the surface of the spherical conductor will be \(V=\frac{1}{4 \pi \varepsilon_{0}} \frac{Q}{R}\).

Capacitance of the spherical conductor situated in vacuum is \(C=\frac{Q}{V}=\frac{Q}{\frac{1}{4 \pi \varepsilon_{0}} \cdot \frac{Q}{R}} \text { or } C=4 \pi \varepsilon_{0} R\) Clearly, the capacitance of a spherical conductor is proportional to its radius.
The radius of the spherical conductor of 1F capacitance is R = \(\frac{1}{4 \pi \varepsilon_{0}}\). C and this radius is about 1500 times the radius of the earth \(\left(\sim 6 \times 10^{3} \mathrm{~km}\right)\).
(i) If an isolated sphere has a capacitance 50pF. Then radius is

(a) 90 ern

(b) 45 cm

(c) 45 m

(d) 90 m

(ii) How much charge should be placed on a capacitance of 25 pF to raise its potential to l0⁵ V?

\(\text { (a) } 1 \mu \mathrm{C}\)

\(\text { (b) } 1.5 \mu \mathrm{C}\)

\(\text { (c) } 2 \mu \mathrm{C}\)

\(\text { (d) } 2.5 \mu \mathrm{C}\)

(iii) Dimensions of capacitance is

\(\text { (a) }\left[M L^{-2} T^{4} A^{2}\right]\)

\(\text { (b) }\left[\mathrm{M}^{-1} \mathrm{~L}^{-1} \mathrm{~T}^{3} \mathrm{~A}^{1}\right]\)

\(\text { (c) }\left[\mathrm{M}^{-} \mathrm{L}^{-2} \mathrm{~T}^{4} \mathrm{~A}^{2}\right]\)

\(\text { (d) }\left[M^{0} L^{-2} T^{4} A^{1}\right]\)

(iv) Metallic sphere of radius R is charged to potential V. Then charge q is proportional to

(a) V

(b) R

(c) both V and R

(d) none of these.

(v) If 64 identical spheres of charge q and capacitance C each are combined to form a large sphere. The charge and capacitance of the large sphere is

(a) 64q, C

(b) 16q, 4C

(c) 64q, 4C

(d) 16q, 64C

4)

A dielectric slab is a substance which does not allow the flow of charges through it but permits them to exert electrostatic forces on one another.
When a dielectric slab is placed between the plates, the field E_o polarises the dielectric. This induces charge -Q_p on the upper surface and + Q_p on the lower surface of the dielectric. These induced charges set up a field E_p inside the dielectric in the opposite direction of \(\vec{E}_{0}\) as shown.

(I) In a parallel plate capacitor, the capacitance increases from \(4 \mu \mathrm{F}\) to 80\(\mu \mathrm{F}\) on introducing a dielectric medium between the plates. What is the dielectric constant of the medium?

(a) 10

(b) 20

(c) 50

(d) 100

(ii) A parallel plate capacitor with air between the plates has a capacitance of 8 pF. The separation between the plates is now reduced half and the space between them is filled with a medium of dielectric constant 5.
Calculate the value of capacitance of the capacitor in second case.

(a) 8pF

(b) 10pF

(c) 80pF

(d) 100pF

(iii) A dielectric introduced between the plates of a parallel plate condenser

(a) decreases the electric field between the plates	(b) increases the capacity of the condenser
(c) increases the charge stored in the condenser	(d) increases the capacity of the condenser

(iv) A parallel plate capacitor of capacitance 1 pF has separation between the plates is d. When the distance of separation becomes 2d and wax of dielectric constant x is inserted in it the capacitance becomes 2 pF. What is the value of x?

(a) 2

(b) 4

(c) 6

(d) 8

(v) A parallel plate capacitor having area A and separated by distance d is filled by copper plate of thickness b. The new capacity is

\(\text { (a) } \frac{\varepsilon_{0} A}{d+\frac{b}{2}}\)

\(\text { (b) } \frac{\varepsilon_{0} A}{2 d}\)

\(\text { (c) } \frac{\varepsilon_{0} A}{d-b}\)

\(\text { (d) } \frac{2 \varepsilon_{0} A}{d+\frac{b}{2}}\)

5)

When an insulator is placed in an external field, the dipoles become aligned. Induced surface charges on the insulator establish a polarization field \(\vec{E}_{i}\) in its interior. The net field \(\vec{E}\) in the insulator is the vector sum of \(\vec{E}_{0}\) and \(\vec{E}_{i}\) as shown in the figure.

On the application of external electric field, the effect of aligning the electric dipoles in the insulator is called polarisation and the field \(\vec{E}_{i}\) is known as the polarisation field.
The dipole moment per unit volume of the dielectric is known as polarisation \((\vec{P})\).
For linear isotropic dielectrics, \(\vec{P}=\chi \vec{E}\) where X = electrical susceptibility of the dielectric medium.
(i) Which among the following is an example of polar molecule?

(a) O₂

(b) H₂

(c) N₂

(d) HCl

(ii) When air is replaced by a dielectric medium of constant K, the maximum force of attraction between two charges separated by a distance

(a) increases K times

(b) remains unchanged

(c) decreases Ktimes

(d) increases 2K times

(iii) Which of the following is a dielectric?

(a) Copper

(b) Glass

(c) Antimony (Sb)

(d) None of these

(iv) For a polar molecule, which of the following statements is true?

(a) The centre of gravity of electrons and protons coincide

(b) The centre of gravity of electrons and protons do not coincide

(c) The charge distribution is always symmetrical.

(d) The dipole moment is always zero.

(v) When a comb rubbed with dry hair attracts pieces of paper. This is because the

(a) comb polarizes the piece of paper

(b) comb induces a net dipole moment opposite to the direction of field

(c) electric field due to the comb is uniform

(d) comb induces a net dipole moment perpendicular to the direction of field

CBSE 12th Standard Physics Subject Electric Charges And Fields Chapter Case Study Questions 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
Smallest charge that can exist in nature is the charge of an electron. During friction it is only the transfer of electrons which makes the body charged. Hence net charge on any body is an integral multiple of charge of an electron.

[1.6 x 10^-19 C] i.e.
q = ± ne
where n = 1,2,3,4, ....
Hence no body can have a charge represented as \(1.1 e, 2.7 e, \frac{3}{5} e, \text { etc. }\)
Recently, it has been discovered that elementary particles such as protons or neutrons are composed of more elemental units called quarks.
(i) Which of the following properties is not satisfied by an electric charge?

(a) Total charge conservation (b) Quantization of charge

(c) Two types of charge (d) Circular line of force

(ii) Which one of the following charges is possible?

(a) 5.8 x 10^-18C (b) 3.2 x 10^-18C

(c) 4.5 x 10^-19C (d) 8.6 x 10^-19C

(iii) If a charge on a body is 1 nC, then how many electrons are present on the body?

(a) 6.25 x 10²⁷ (b) 1.6 x 10¹⁹

(c) 6.25 x 10²⁸ (d) 6.25 x 10⁹

(iv) If a body gives out 10⁹ electrons every second, how much time is required to get a total charge of 1 C from it?

(a) 190.19 years (b) 150.12 years (c) 198.19 years (d) 188.21 years

(v) A polythene piece rubbed with wool is found to have a negative charge of3.2 x 1O^-7C.Calculate the number of electrons transferred.

(a) 2 x 10¹² (b) 3 x 10¹² (c) 2 x 10¹⁴ (d) 3 x 10¹⁴
2)
In 1909, Robert Millikan was the first to find the charge of an electron in his now-famous oil-drop experiment. In that experiment, tiny oil drops were sprayed into a uniform electric field between a horizontal pair of oppositely charged plates. The drops were observed with a magnifying eyepiece, and the electric field was adjusted so that the upward force on some negatively charged oil drops was just sufficient to balance the downward force of gravity. That is, when suspended, upward force qE just equaled Mg. Millikan accurately measured the charges on many oil drops and found the values to be whole number multiples of 1.6 x 10^-19 C the charge of the electron. For this, he won the Nobel prize.

(i) If a drop of mass 1.08 x 10^-14kg remains stationary in an electric field of 1.68 x 10⁵ N C^-I, then the charge of this drop is

(a) 6.40 x 10^-19 C (b) 3.2 x 10^-19 C

(c) 1.6 X 10^-19 C (d) 4.8 x 10^-19 C

(ii) Extra electrons on this particular oil drop (given the presently known charge of the electron) are

(a) 4 (b) 3 (c) 5 (d) 8

(iii) A negatively charged oil drop is prevented from falling under gravity by applying a vertical electric field 100 V m^-1.If the mass of the drop is 1.6 X 10^-3 g, the number of electrons carried by the drop is (g= 10 m s^-2)

(a) 10¹⁸ (b) 10¹⁵ (c) 10¹² (d) 10⁹

(iv) The important conclusion given by Millikan's experiment about the charge is

(a) charge is never quantized (b) charge has no definite value

(c) charge is quantized (d) charge on oil drop always increases.

(v) If in Millikan's oil drop experiment, charges on drops are found to be \(8 \mu \mathrm{C}, 12 \mu \mathrm{C}, 20 \mu \mathrm{C}\) then quanta of charge is

\(\text { (a) } 8 \mu \mathrm{C}\) \(\text { (b) } 20 \mu \mathrm{C}\) \(\text { (c) } 12 \mu \mathrm{C}\) \(\text { (d) } 4 \mu \mathrm{C}\)

3)

Electric field strength is proportional to the density of lines of force i.e., electric field strength at a point is proportional to the number of lines of force cutting a unit area element placed normal to the field at that point. As illustrated in the given figure, the electric field at P is stronger that at Q.

(i) Electric lines of force about a positive point charge are

(a) radially outwards	(b) circular clockwise
(c) radially inwards	(d) parallel straight lines

(ii) Which of the following is false for electric lines of force?

(a) They always start from positive charges and terminate on negative charges

(b) They are always perpendicular to the surface of a charged conductor

(c) They always form closed loops

(d) They are parallel and equally spaced in a region of uniform electric field

(iii) Which one of the following pattern of electric line of force in not possible in filed due to stationary charges?

(iv) Electric lines of force are curved

(a) in the field of a single positive or negative charge	(b) in the field of two equal and opposite charges
(c) in the field of two like charges	(d) both (b) and (c).

(v) The figure below shows the electric field lines due to two positive charges. The magnitudes E_A, E_B and E_c of the electric fields at points A, Band C respectively are related as

\(\text { (a) } E_{A}>E_{B}>E_{C}\)

\(\text { (b) } E_{B}>E_{A}>E_{C}\)

\(\text { (c) } E_{A}=E_{B}>E_{C}\)

\(\text { (d) } E_{A}>E_{B}=E_{C}\)

4)
In practice, we deal with charges much greater in magnitude than the charge on an electron, so we can ignore the quantum nature of charges and imagine that the charge is spread in a region in a continuous manner. Such a charge distribution is known as continuous charge distribution. There are three types of continuous charge distribution : (i) Line charge distribution (ii) Surface charge distribution (iii) Volume charge distribution as shown in figure.

(I) Statement 1 : Gauss's law can't be used to calculate electric field near an electric dipole.
Statement 2 : Electric dipole don't have symmetrical charge distribution.

(a) Statement 1 and statement 2 are true (b) Statement 1 is false but statement 2 is true

(c) Statement 1 is true but statement 2 is false (d) Both statements are false

(ii) An electric charge of 8.85 X 10^-13 C is placed at the centre of a sphere of radius 1 m. The electric flux through the sphere is

(a) 0.2 N C^-1m² (b) 0.1 N C^-1 m² (c) 0.3 N C^-1 m² (d) 0.01 N C^-1m²

(iii) The electric field within the nucleus is generally observed to be linearly dependent on r. So,

(a) a=O \(\text { (b) } a=\frac{R}{2}\) (c) a=-R \(\text { (d) } a=\frac{2 R}{3}\)

(iv) What charge would be required to electrify a sphere of radius 25 cm so as to get a surface charge density of \(\frac{3}{\pi} \mathrm{C} \mathrm{m}^{-2} ?\)

(a) 0.75 C (b) 7.5 C (c) 75 C (d) zero

(v) The SI unit of linear charge density is

(a) Cm (b) Cm^-1 (c) C m^-2 (d) C m^-3

5)

Surface charge density is defined as charge per unit surface area of surface charge distribution. i.e., \(\sigma=\frac{d q}{d S}\) Two large. thin metal plates are parallel and close to each other. On their inner faces, the plates have surface charge densities of opposite signs having magnitude of 17.0 x 10^-22 C m^-2as shown. The intensity of electric field at a point is \(E=\frac{\sigma}{\varepsilon_{0}}\) where \(\varepsilon_{0}\) = permittivity of free space.

(i) E in the outer region of the first plate is

\(\text { (a) } 17 \times 10^{-22} \mathrm{~N} / \mathrm{C}\)

\(\text { (b) } 1.5 \times 10^{-25} \mathrm{~N} / \mathrm{C}\)

\(\text { (c) } 1.9 \times 10^{-10} \mathrm{~N} / \mathrm{C}\)

(d) zero

(ii) E in the outer region of the second plate is

\(\text { (a) } 17 \times 10^{-22} \mathrm{~N} / \mathrm{C}\)

\(\text { (b) } 1.5 \times 10^{-15} \mathrm{~N} / \mathrm{C}\)

\(\text { (c) } 1.9 \times 10^{-10} \mathrm{~N} / \mathrm{C}\)

(d) zero

(iii) E between the plates is

\(\text { (a) } 17 \times 10^{-22} \mathrm{~N} / \mathrm{C}\)

\(\text { (b) } 1.5 \times 10^{-15} \mathrm{~N} / \mathrm{C}\)

\(\text { (c) } 1.9 \times 10^{-10} \mathrm{~N} / \mathrm{C}\)

(d) zero

(iv) The ratio of E from right side of B at distances 2 cm and 4 ern, respectively is

(a) 1: 2

(b) 2: 1

(c) 1: 1

\(\text { (d) } 1: \sqrt{2}\)

(v) In order to estimate the electric field due to a thin finite plane metal plate, the Gaussian surface considered is

(a) spherical

(b) cylindrical

(c) straight line

(d) none of these

CBSE 12th Standard Physics Subject Semiconductor Electronics Materials Devices And Simple Circuits Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
A silicon p-n junction diode is connected to a resistor R and a battery of voltage V_B through milliammeter (mA) as shown in figure. The knee voltage for this junction diode is V_N = 0.7 V. The p-n junction diode requires a minimum current of 1m. A to attain a value higher than the knee point on the J- V characteristics of this junction diode. Assuming that the voltage V across the junction is independent of the current above the knee point. A p-n junction is the basic building block of many semiconductor devices like diodes. Important process occurring during the formation of a p-n junction are diffusion and drift. In an n-type semiconductor concentration of electrons is more as compared to holes. In a p-type semiconductor concentration of holes is more as compared to electrons.

(i) If V_B= 5 V, the maximum value of R so that the voltage V is above the knee point voltage is

(a) 40 \(\Omega\) (b) 4.3 \(\Omega\) (c) 5.0 \(\Omega\) (d) 5.7 \(\Omega\)

(ii) If V_B = 5 V, the value of R in order to establish a current to 6 mA in the circuit is

(a) 833 \(\Omega\) (b) 717 \(\Omega\) (c) 950 \(\Omega\) (d) 733 \(\Omega\)

(iii) If V_B = 6 V, the power dissipated in the resistor R, when a current of 6 mA flows in the circuit is

(a) 30.2 mW (b) 30.8 mW (c) 31.2 mW (d) 31.8 mW

(iv) When the diode is reverse biased with a voltage of 6 V and V_bi = 0.63 V. Calculate the total potential.

(a) 9.27 V (b) 6.63 V (c) 5.27 V (d) 0.63 V

(v) Which of the below mentioned statement is false regarding a p-n junction diode?

(a) Diodes are uncontrolled devices. (b) Diodes are rectifying devices.

(c) Diodes are unidirectional devices. (d) Diodes have three terminals

2)

The electron mobility characterises how quickly an electron can move through a metal of semiconductor when pulled by an electric field. There is an analogous quality for holes, called hole mobility. A block of pure silicon at 300 K has a length of 10 cm and an area of 1.0 cm². A battery of emf 2 V is connected across it. The mobility of electron is 0.14 m² y^-1 s^-1 and their number density is 1.5 x 10¹⁶ m^-3. The mobility of holes is 0.05 m² y^-1 s^-1.
(i) The electron current is

(a) 6.72 x 10^-4 A

(b) 6.72 x 10^-5 A

(c) 6.72 x 10^-6 A

(d) 6.72 x 10^-7A

(ii) The hole current is

(a) 2.0 x 10-7 A

(b) 2.2 x 10-7 A

(c) 2.4 X 10-7 A

(d) 2.6 x 10-7 A

(iii) The number density of donor atoms which are to be added up to pure silicon semiconductor to produce an n-type semiconductor of conductivity 6.4 \(\Omega\)^-1 cm^-1 is approximately (neglect the contribution of holes to conductivity)

(a) 3 x 10²² m^-3

(b) 3 x 10²³ m^-3

(c) 3 x 10²⁴ m^-3

(d) 3 x 10²¹ m^-3

(iv) When the given silicon semiconductor is doped with indium, the hole concentration increases to 4.5 x 10²³ m^-3. The electron concentration in doped silicon is

(a) 3 x 10⁹ m^-3

(b) 4 x 10⁹ m^-3

(c) 5 x 10⁹ m^-3

(d) 6 x 10⁹ m^-3

(v) Pick out the statement which is not correct.

(a) At a low temperature, the resistance of a semiconductor is very high.

(b) Movement of holes is restricted to the valence band only

(c) Width of the depletion region increases as the forward bias voltage increases in case of a p- n junction diode.

(d) In a forward bias condition, the diode heavily conducts

3)

p-n junction is a single crystal of Ge or Si doped in such a manner that one half portion of it acts as p-type semiconductor and other half functions as n-type semiconductor. As soon as a p-n junction is formed, the holes from the p-region diffuse into the n-region and electron from n region diffuse in to p-region. This results in the development of VB across the junction which opposes the further diffusion of electrons and holes through the junction.
(i) In an unbiased p-n junction electrons diffuse from n-region to p-region because

(a) holes in p-region attract them

(b) electrons travel across thejunction due to potential difference

(c) electron concentration in n-region is more as compared to that in p-region

(d) only electrons move from n to p region and not the vice-versa

(ii) Electron hole recombination in p-n junction may lead to emission of

(a) light

(b) ultraviolet rays

(c) sound

(d) radioactive rays

(iii) In an unbiased p-n junction

(a) potential at p is equal to that at n	(b) potential at pis +ve and that at n is -ve
(c) potential at p is more than that at n	(d) potential at p is less than that at n.

(iv) The potential of depletion layer is due to

(a) electrons

(b) holes

(c) ions

(d) forbidden band

(v) In the depletion layer of unbiased p-n junction

(a) it is devoid of charge carriers	(b) has only electrons
(c) has only holes	(d) p-n junction has a weak electric field

4)
The potential barrier in the p-n junction diode is the barrier in which the charge recquires additional force for crossing the region. In other words, the barrier in which the charge carrier stopped by the obstructive force is known as the potential barrier.
When a p-type semiconductor is brought into a close contact with n-type semiconductor, we get a p-n junction with a barrier potential 0.4 V and width of depletion region is 4.0 x 10^-7 m. This p-n junction is forward biased with a battery of voltage 3V and negligible internal resistance, in series with a resistor of resistance R, ideal millimeter and key K as shown in figure. When key is pressed, a current of 20 mA passes through the diode.
(i) The intersity of the electric field in the depletion region when p-n junction is unbiased is

(a) 0.5 x 10⁶ V m^-1 (b) 1.0 x 10⁶ V m^-1 (c) 2.0 x 10⁶ V m^-1 (d) 1.5 x 10⁶ V m^-1

(ii) The resistance of resistor R is

(a) 150 \(\Omega\) (b) 300 \(\Omega\) (c) l30 \(\Omega\) (d) 180 \(\Omega\)

(iii) In a p-n junction, the potential barrier is due to the charges on either side of the junction, these charges are

(a) majority carriers (b) minority carriers

(c) both (a) and (b) (d) fixed donor and acceptor ions.

(iv) If the voltage of the potential barrier is V₀ A voltage V is applied to the input, at what moment will the barrier disappear?

(a) V0 (b) V=V₀ (c) V>V₀ (d) V<0

(v) If an electron with speed 4.0 x 10⁵ m s^-1 approaches the p-n junction from the n-side, the speed with which it will enter the p-side is

(a) 1.39 x 10⁵ m S^-1 (b) 2.78 x 10⁵ m S^-1 (c) 1.39 x 10⁶ m S^-1 (d) 2.78 x 10⁶ m s^-1
5)
Solar cell is a p-n junction diode which converts solar energy into electric energy. It is basically a solar energy converter. The upper layer of solar cell is of p- type semiconductor and very thin so that the incident light photons may easily reach the p-n junction. On the top face of p-layer, the metal finger electrodes are prepared in order to have enough spacing between the fingers for the lights to reach the p-n junction through p-layer.
(i) The schematic symbol of solar cell is

(ii) The p-n jqnction which generates an emf when solar radiations fall an it, with no external bias applied,is a

(a) light emitting diode (b) photodiode (c) solar cell (d) None of these

(iii) For satellites the source of energy is

(a) Solar cell (b) Fuel cell (c) Edison cell (d) None of these

(iv) Which of the following material is used in solar cell?

(a) Barium (b) Silicon (c) Silver (d) Selenium

(v) The efficiency of a solar cell may be in the range

(a) 2 to 5% (b) 10 to 15% (c) 30 to 40% (d) 70 to 80%

CBSE 12th Standard Physics Subject Nuclei Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
In the year 1939, German scientist Otto Hahn and Strassmann discovered that when an uranium isotope was bombarded with a neutron, it breaks into two intermediate mass fragments. It was observed that, the sum of the masses of new fragments formed were less than the mass of the original nuclei. This difference in the mass appeared as the energy released in the process. Thus, the phenomenon of splitting of a heavy nucleus (usually A> 230) into two or more lighter nuclei by the bombardment of proton, neutron, a-particle, etc with liberation of energy is called nuclear fission.
\({ }_{92} \mathrm{U}^{235}+{ }_{0} n^{1} \rightarrow \quad{ }_{92} \mathrm{U}^{236} \rightarrow{ }_{56} \mathrm{Ba}^{144}+{ }_{36} \mathrm{Kr}^{89}+3{ }_{0} n^{1}+Q\)
Unstable nucleus
(i) Nuclear fission can be explained on the basis of

(a) Millikan's oil drop method

(b) Liquid. drop model

(c) Shell model

(d) Bohr's model

(ii) For sustaining the nuclear fission chain reaction in a sample (of small size) \({ }_{92}^{235} \mathrm{U}\), it is desirable to slow down fast neutrons by

(a) friction (b) elastic damping/scattering

(c) absorption (d) none of these

(iii) Which of the following is/are fission reaction(s)?
\(\text {(I) }{ }_{0}^{1} n+{ }_{92}^{235} \mathrm{U} \rightarrow{ }_{92}^{236} \mathrm{U} \rightarrow{ }_{51}^{133} \mathrm{Sb}+{ }_{41}^{99} \mathrm{Nb}+4_{0}^{1} n\)
\(\text {(II) }{ }_{0}^{1} n+{ }_{92}^{235} \mathrm{U} \rightarrow{ }_{54}^{1.40} \mathrm{Xe}+{ }_{38}^{94} \mathrm{Sr}+2{ }_{0}^{1} n\)
\((\mathrm{III}){ }_{1}^{2} \mathrm{H}+{ }_{1}^{2} \mathrm{H} \rightarrow{ }_{2}^{3} \mathrm{He}+{ }_{0}^{1} n\)

(a) Both II and III (b) Both I and III

(c) Only II (d) Both I and II

(iv) On an average, the number of neutrons and the energy of a neutron released per fission of a uranium atom are respectively

(a) 2.5 and 2 keV (b) 3 and 1 keV (c) 2.5 and 2 MeV (d) 2 and 2 keV

(v) In any fission process, ratio of mass of daughter nucleus to mass of parent nucleus is

(a) less than 1 (b) greater than 1

(c) equal to 1 (d) depends 0 the mass of parent nucleus
2)
The nucleus was first discovered in 1911 by Lord Rutherford and his associates by experiments on scattering of a-particles by atoms. He found that the scattering results could be explained, if atoms consist of a small, central, massive and positive core surrounded by orbiting electrons. The experimental results indicated that the size of the nucleus is of the order of 10^-14m and is thus 10000 times smaller than the size of atom.
(i) Ratio of mass of nucleus with mass of atom is approximately

(a) 1 (b) 10 (c) 10³ (d) 10¹⁰

(ii) Masses of nuclei of hydrogen, deuterium and tritium are in ratio

(a) 1:2:3 (b) 1:1:1 (c) 1:1:2 (d) 1:2:4

(iii) Nuclides with same neutron number but different atomic number are

(a) isobars (b) isotopes (c) isotones (d) none of these

(iv) If R is the radius and A is the mass number, then log R versus log A graph will be

(a) a straight line (b) aparabola (c) anellipse (d) none of these

(v) The ratio of the nuclear radii of the gold isotope \({ }_{79}^{197} \mathrm{Au}\) and silver isotope \({ }_{47}^{107} \mathrm{Au}\) is

(a) 1.23 (b) 0.216 (c) 2.13 (d) 3.46

3)

A heavy nucleus breaks into comparatively lighter nuclei which are more stable compared to the original heavy nucleus. When a heavy nucleus like uranium is bombarded by slow moving neutrons, it splits into two parts releasing large amount of energy. The typical fission reaction of \({ }_{92} \mathrm{U}^{235}\).
\({ }_{92} \mathrm{U}^{235}+{ }_{0} n^{1} \rightarrow{ }_{56} \mathrm{Ba}^{141}+{ }_{36} \mathrm{Kr}^{92}+3{ }_{0} n^{1}+200 \mathrm{MeV}\)
The fission of ₉₂U²³⁵approximately released 200 MeV of energy.
(i) If 200 MeV energy is released in the fission of a single nucleus of \({ }_{92}^{235} \mathrm{U}\),the fissions which are required to produce a power of 1kW is

(a) 3.125 x 10¹³

(b) 1.52 x 10⁶

(c) 3.125 x 10¹²

(d) 3.125 x 10¹⁴

(ii) The release in energy in nuclear fission is consistent with the fact that uranium has

(a) more mass per nucleon than either ofthe two fragments

(b) more mass per nucleon as the two fragment

(c) exactly the same mass per nucleon as the two fragments

(d) less mass per nucleon than either of two fragments.

(iii) When ₉₂U²³⁵undergoes fission, about 0.1% of the original mass is converted into energy. The energy released when 1 kg of ₉₂U²³⁵undergoes fission is

(a) 9 x 10¹¹J

(b) 9 x 10¹³J

(c) 9 x 10¹⁵J

(d) 9 x 10¹⁸J

(iv) A nuclear fission is said to be critical when multiplication factor or K

(a) K= 1

(b) K> 1

(c) K< 1

(d) K=0

(v) Einstein's mass-energy conversion relation E = mc² is illustrated by

(a) nuclear fission

(b) \(\beta\)-decay

(c) rocket propulsion

(d) steam engine

4)
Neutrons and protons are identical particle in the sense that their masses are nearly the same and the force, called nuclear force, does into distinguish them. Nuclear force is the strongest force. Stability of nucleus is determined by the neutron proton ratio or mass defect or packing fraction. Shape of nucleus is calculated by quadrupole moment and spin of nucleus depends on even or odd mass number. Volume of nucleus depends on the mass number. Whole mass of the atom (nearly 99%) is centred at the nucleus.
(i) The correct statements about the nuclear force is/are

(a) change independent (b) short range force

(c) non-conservative force (d) all of these.

(ii) The range of nuclear force is the order of

(a) 2 x 10^-10 m (b) 1.5 x 10^-20 m (c) 1.2 x 10^-4 m (d) 1.4 x 10^-15 m

(iii) A force between two protons is same as the force between proton and neutron. The nature of the force is

(a) electrical force (b) weak nuclear force (c) gravitational force (d) strong nuclear force.

(iv) Two protons are kept at a separation of 40 \(\dot A\). Fn is the nuclear force and F_e is the electrostatic force between them. Then

(a) F_n << F_e (b) F_n = F_e (c) F_n >> F_e (d) F_n \(\approx \) F_e

(v) All the nucleons in an atom are held by

(a) nuclear forces (b) van der Waal's forces

(c) tensor forces (d) coulomb forces

5)

The density of nuclear matter is the ratio of the mass of a nucleus to its volume. As the volume of a nucleus is directly proportional to its mass number A, so the density of nuclear matter is independent of the size of the nucleus. Thus, the nuclear matter behaves like a liquid of constant density. Different nuclei are like drops of this liquid, of different sizes but of same density.
Let A be the mass number and R be the radius of a nucleus. If m is the average mass of a nucleon, then
Mass of nucleus = mA
\(\text { Volume of nucleus }=\frac{4}{3} \pi R^{3}=\frac{4}{3} \pi\left(R_{0} A^{1 / 3}\right)^{3}=\frac{4}{3} \pi R_{0}^{3} A\)
\(\text { Nuclear density, } \rho_{\mathrm{nu}}=\frac{\text { Mass of nucleus }}{\text { Volume of nucleus }} \text { or } \rho_{\mathrm{nu}}=\frac{m A}{\frac{4}{3} \pi R_{0}^{3} A}=\frac{3 m}{4 \pi R_{0}^{3}}\)
Clearly, nuclear density is independent of mass number A or the size of the nucleus. The nuclear mass density is of the order 10¹⁷ kg m^-3. This density is very large as compared to the density of ordinary matter, say water, for which p = 1.0 x 10³ kg m^-3.
(i) The nuclear radius of \({ }_{8}^{16} \mathrm{O}\) is 3 X 10^-15 m. The density of nuclear matter is

(a) 2.9 x 10³⁴ kg m^-3

(b) 1.2 x 10¹⁷kg m^-3

(c) 16 x 10²⁷kg m^-3

(d) 2.4 x 10¹⁷kg m^-3

(ii) What is the density of hydrogen nucleus in SI units? Given R_o = 1.1 fermi and m_p = 1.007825 amu

(a) 2.98 x 10¹⁷kg m^-3

(b) 3.0 x 10³⁴ kg m^-3

(c) 1.99 x 10¹¹kg m^-3

(d) 7.85 x 10¹⁷kg m^-3

(iii) Density of a nucleus is

(a) more for lighter elements and less for heavier elements.

(b) more for heavier elements and less for lighter elements

(c) very less compared to ordinary matter

(d) a constant

(iv) The nuclear mass of \({ }_{26}^{56} \mathrm{Fe}\) is 55.85 amu. The its nuclear density is

(a) 5.0 x 10¹⁹kg m^-3.

(b) 1.5 x 10¹⁹kg m^-3

(c) 2.9 x 10¹⁷kg m^-3

(d) 9.2 x 10²⁶kg m^-3

(v) If the nucleus of \({ }_{13}^{27} \mathrm{Al}\) has a nuclear radius of about 3.6 fm, then \({ }_{52}^{125} \mathrm{Te}\) would have its radius approximately as

(a) 9.6 fm

(b) 12 fm

(c) 4.8 fm

(d) 6 fm

CBSE 12th Standard Physics Subject Atoms Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)

Niels Bohr introduced the atomic Hydrogen model in 1913. He described it as a positively charged nucleus, comprised of protons and neutrons, surrounded by a negatively charged electron cloud. In the model, electrons orbit the nucleus in atomic shells. The atom is held together by electrostatic forces between the positive nucleus and negative surroundings.

Bohr correctly proposed that the energy and radii of the orbits of electrons in atoms are quantized, with energy for transitions between orbits given by
\(\Delta E=h v=E_{i}-E_{f}\) Where \(\Delta E\) is the change in energy between the initial and final orbits and hv is the energy of an absorbed or emitted photon.
(i) In the Bohr model of the hydrogen atom, discrete radii and energy states result when an electron circles the atom in an integer number of

(a) de Broglie wavelengths	(b) wave frequencies
(c) quantum numbers	(d) diffraction patterns.

(ii) The angular speed of the electron in the n^th orbit of Bohr's hydrogen atom is

(a) directly proportional to n	(b) inversely proportional to \(\sqrt{n}\)
(c) inversely proportional to n²	(d) inversely proportional to n³

(iii) When electron jumps from n = 4 level to n = 1 level, the angular momentum of electron changes by

\(\text { (a) } \frac{h}{2 \pi}\)

\(\text { (b) } \frac{h}{\pi}\)

\(\text { (c) } \frac{3 h}{2 \pi}\)

\(\text { (d) } \frac{2 h}{\pi}\)

(iv) The lowest Bohr orbit in hydrogen atom has

(a) the maximum energy	(b) the least energy
(c) infinite energy	(d) zero energy

(v) Which of the following postulates of the Bohr modelled to the quantization of energy of the hydrogen atom?

(a) The electron goes around the nucleus in circular orbits.

(b) The angular momentum of the electron can only be an integral multiple of h/2\(\pi\)

(c) The magnitude of the linear momentum of the electron is quantized.

(d) Quantization of energy is itself a postulate of the Bohr model.

2)

In 1911, Rutherford, along with his assistants, H. Geiger and E. Marsden, performed the alpha particle scattering experiment. H. Geiger and E. Marsden took radioactive source \(\left(\begin{array}{c} 214 \\ 83 \end{array} \mathrm{Bi}\right)\) for a-particles. A collimated beam of a-particles of energy 5.5 MeV was allowed to fall on 2.1 x 10^-7m thick gold foil. The a-particles were observed through a rotatable detector consisting of a Zinc sulphide screen and microscope. It was found that a-particles got scattered. These scattered a-particles produced scintillations on the zinc sulphide screen. Observations of this experiment are as follows.
(I) Most of the a-particles passed through the foil without deflection.
(II) Only about 0.14% of the incident a-particles scattered by more than 1°.
(III) Only about one a-particle in every 8000 a-particles deflected by more than 90°.
These observations led to many arguments and conclusions which laid down the structure of the nuclear model of an atom.

(i) Rutherford's atomic model can be visualised as

(ii) Gold foil used in Geiger-Marsden experiment is about 10^-8 m thick. This ensures

(a) gold foil's gravitational pull is small or possible

(b) gold foil is deflected when a-particle stream is not incident centrally over it

(c) gold foil provides no resistance to passage of a-particles

(d) most a-particle will not suffer more than 1° scattering during passage through gold foil

(iii) In Geiger-Marsden scattering experiment, the trajectory traced by an a-particle depends on

(a) number of collision	(b) number of scattered a- particles
(c) impact parameter	(d) none of these

(iv) In the Geiger-Marsden scatteririg experiment, in case of head-on collision, the impact parameter should be

(a) maximum	(b) minimum
(c) infinite	(d) zero

(v) The fact only a small fraction of the number of incident particles rebound back in Rutherford scattering indicates that

(a) number of a-particles undergoing head-on-collision is small

(b) mass of the atom is concentrated in a small volume

(c) mass of the atom is concentrated in a large volume

(d) both (a) and (b).

3)

At room temperature, most of the H-atoms are in ground state. When an atom receives some energy (i.e., by electron collisions), the atom may acquire sufficient energy to raise electron to higher energy state. In this condition, the atom is said to be in excited state. From the excited state, the electron can fall back to a state of lower energy emitting a photon equal to the energy difference of the orbit.

In a mixture of H-He⁺ gas (He+ is single ionized He atom), H-atoms and He⁺ ions are excited to their respective first excited states. Subsequently, H-atoms transfer their total excitation energy to He⁺ ions (by collisions).
(i) The quantum number n of the state finally populated in He⁺ ions is

(a) 2

(b) 3

(c) 4

(d) 5

(ii) The wavelength of light emitted in the visible region by He⁺ ions after collisions with H-atoms is

(a) 6.5 x 10^-7 m

(b) 5.6 x 10^-7 m

(c) 4.8 x 10^-7 m

(d) 4.0 x 10^-7 m

(iii) The ratio of kinetic energy of the electrons for the H-atoms to that of He⁺ ion for n = 2 is

\(\text { (a) } \frac{1}{4}\)

\(\text { (b) } \frac{1}{2}\)

(c) 1

(d) 2

(iv) The radius ofthe ground state orbit of H-atoms is

\(\text { (a) } \frac{\varepsilon_{0}}{h \pi m e^{2}}\)

\(\text { (b) } \frac{h^{2} \varepsilon_{0}}{\pi m e^{2}}\)

\(\text { (c) } \frac{\pi m e^{2}}{h}\)

\(\text { (d) } \frac{2 \pi h \varepsilon_{0}}{m e^{2}}\)

(v) Angular momentum of an electron in H-atom in first excited state is

\(\text { (a) } \frac{h}{\pi}\)

\(\text { (b) } \frac{h}{2 \pi}\)

\(\text { (c) } \frac{2 \pi}{h}\)

\(\text { (d) } \frac{\pi}{h}\)

4)

Bohr's model explains the spectral lines of hydrogen atomic emission spectrum. While the electron of the atom remains in the ground state, its energy is unchanged. When the atom absorbs one or more quanta of energy, the electrons moves from the ground state orbit to an excited state orbit that is further away.

The given figure shows an energy level diagram of the hydrogen atom. Several transitions are marked as I, II, III and so on. The diagram is only indicative and not to scale.
(i) In which transition is a Balmer series photon absorbed?

(a) II

(b) III

(c) IV

(d) VI

(ii) The wavelength of the radiation involved in transition II is

(a) 291 nm

(b) 364 nm

(c) 487 nm

(d) 652 nm

(iii) Which transition will occur when a hydrogen atom is irradiated with radiation of wavelength 103 nm?

(a) I

(b) II

(c) IV

(d) V

(iv) The electron in a hydrogen atom makes a transition from n = n₁ to n = n₂ state. The time period of the electron in the initial state is eight times that in the final state. The possible values of n₁ and n₂ are

(a) n₁ = 4, n₂= 2

(b) n₁ = 8, n₂= 2

(c) n₁ = 8, n₂= 3

(d) n₁= 6, n₂= 2

(v) The Balmer series for the H-atom can be observed

(a) if we measure the frequencies of light emitted when an excited atom falls to the ground state

(b) if we measure the frequencies of light emitted due to transitions between excited states and the first excited state.

(c) in any transition in a H-atom

(d) none of these.

5)
The spectral series of hydrogen atom were accounted for by Bohr using the relation \(\bar{v}=R\left(\frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}}\right)\),
where R = Rydberg constant = 1.097 x 10⁷ m.
Lyman series is obtained when an electron jumps to first orbit from any subsequent orbit. Similarly, Balmer series is obtained when an electron jumps to 2^nd orbit from any subsequent orbit, Paschen series is obtained when an electron jumps to 3^rd orbit from any subsequent orbit. Whereas Lyman series lies in U.V. region, Balmer series is in visible region and Paschen series lies in infrared region. Series limit is obtained when n₂ = \(\infty\)
(i) The wavelength of first spectral line of Lyman series is

(a) 1215.4 \(\dot A\) (b) 1215.4 crn (c) 1215.4 m (d) 1215.4 mm

(ii) The wavelength limit of Lyman series is

(a) 1215.4 \(\dot A\) (b) 511.9 \(\dot A\) (c) 951.6 \(\dot A\) (d) 911.6 \(\dot A\)

(iii) The frequency of first spectral line of Balmer series is

(a) 1.097 x 10⁷ Hz (b) 4.57 x 10¹⁴ Hz (c) 4.57 x 10¹⁵ Hz (d) 4.57 x 10¹⁶ Hz

(iv) Which of the following transitions in hydrogen atoms emit photons of highest frequency?

(a) n = 1 to n = 2 (b) n = 2 to n = 6 (c) n = 6 to n = 2 (d) n = 2 to n = 1

(v) The ratio of minimum to maximum wavelength in Balmer series is

(a) 5:9 (b) 5:36 (c) 1:4 (d) 3: 4

CBSE 12th Standard Physics Subject Dual Nature of Radiation and Matter Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
If we allow radiations of a fixed frequency to fall on plate and the accelerating potential difference between the two electrodes is kept fixed, then the photoelectric current is found to increase linearly with the intensity of incident radiation. Here, radiation pressure is P = \(\left(\frac{1+e}{C}\right) I\). As, atmosphere pressure at sea level is 10⁵Pa. If the intensity of light of a given wavelength, is increased, there is an increase in the number of photons incident on a given area in a given time. But the energy of each photon remain the same.
(i) The number of photons hitting the cone second

\(\text { (a) } \pi R^{2} I / 2 E\) \(\text { (b) } 2 \pi R^{2} I / E\) \(\text { (c) } \pi R^{2} I / 4 E\) \(\text { (d) } \pi R^{2} I / E\)

(ii) A radiation of energy E falls normally on a perfect reflecting surface. The momentum transferred to the surface is

\(\text { (a) } \frac{E}{c}\) \(\text { (b) } \frac{2 E}{c}\) \(\text { (c) } E c\) \(\text { (d) } \frac{E}{c^{2}}\)

(iii) Which one is correct?

\(\text { (a) } E^{2}=p^{2} c^{2}\) \(\text { (b) } E^{2}=p^{2} c\) \(\text { (c) } E^{2}=p^{2}\) \(\text { (d) } E^{2}=\frac{p^{2}}{c^{2}}\)

(iv) The incident intensity on a horizontal surface at sea level from the Sun is about 1 k W m^-2. Assuming that 50% of this intensity is reflected and 50% is absorbed, determine the radiation pressure on this horizontal surface.

(a) 8.2 x 10^-2 Pa (b) 5 x 10^-6 Pa (c) 3 x 10^-5 Pa (d) 6 x 10^-5 Pa

(v) Find the ratio of radiation pressure to atmospheric pressure P₀ about 1 x 10⁵ Pa at sea level.

(a) 5 x 10^-11 (b) 4 x 10^-8 (c) 6 x 10^-12 (d) 8 x 10^-11

2)

According to de-Broglie, a moving material particle sometimes acts as a wave and sometimes as a particle or a wave associated with moving material particle which controls the particle in every respect. The wave associated with moving particle is called matter wave or de-Broglie wave where wavelength called de-Broglie wavelength is given by \(\lambda=\frac{h}{m v}\)

(i) If a proton and an electron have the same de Broglie wavelength, then

(a) kinetic energy of electron < kinetic energy of proton

(b) kinetic energy of electron = kinetic energy of proton

(c) momentum of electron = momentum of proton

(d) momentum of electron < momentum of proton

(ii) Which of these particles having the same kinetic energy has the largest de Broglie wavelength?

(a) Electron

(b) Alpha particle

(c) Proton

(d) Neutron

(iii) Two particles A₁ and A₂ of masses m₁ m₂ (m₁ > m₂) have the same de Broglie wavelength. Then

(a) their momenta are the same.	(b) their energies are the same.
(c) momentum of A₁ is less than the momentum of A₂.	(d) energy of A₁ is more than the energy of A₂.

(iv) When the velocity of an electron increases, its de Broglie wavelength

(a) increases

(b) decreases

(c) remains same

(d) may increase or decrease

(v) Proton and a-particle have the same de-Broglie wavelength. What is same for both of them?

(a) time period

(b) energy

(c) frequency

(d) momentum

3)
According to wave theory, the light of any frequency can emit electrons from metallic surface provided the intensity of light be sufficient to provided necessary energy for emission of electrons, but according to experimental observations, the light of frequency less than threshold frequency can not emit electrons; whatever be the intensity of incident light. Einstein also proposed that electromagnetic radiation is quantised.If photoelectrons are ejected from a surface when light of wavelength \(\lambda\) ₁= 550 nm is incident on it. The stopping potential for such electrons is V_s = 0.19 V. Suppose the radiation of wavelength \(\lambda\)₂= 190 nm is incident on the surface.
(i) Photoelectric effect supports quantum nature oflight because
(A) there is a minimum frequency of light below which no photoelectrons are emitted.
(B) the maximum K.E. of photoelectric depends only on the frequency of light and not on its intensity.
(C) even when the metal surface is faintly illuminated, the photo electrons leave the surface immediately.
(D) electric charge of the photoelectrons is quantized.

(a) A,B,C (b) B,C (c) C,D (d) A,D,C

(ii) In photoelectric effect, electrons are ejected from metals, if the incident light has a certain minimum

(a) wavelength (b) frequency (c) amplitude (d) angle of incidence

(iii) Calculate the stopping potential V_S2of surface.

(a) 4.47 (b) 3.16 (c) 2.76 (d) 5.28

(iv) Calculate the work function of the surface.

(a) 3.75 (b) 2.07 (c) 4.20 (d) 3.60

(v) Calculate the threshold frequency for the surface.

(a) 500 x 10¹² Hz (b) 480 x 10¹³ Hz (c) 520 x 10¹¹Hz (d) 460 x 10¹³ Hz
4)
The photon picture of electromagnetic radiations and the characteristic properties of photons are as follows:In the interaction of radiation with matter, radiation behaves as if it is made of particles like photons. Each photon has energy \(E(=h v=h c / \lambda)\) and momentum \(p\left(=\frac{h v}{c}=\frac{h}{\lambda}\right)\) where h is Planck's constant, v and A are the frequency and wavelength of radiation and c is the velocity of light. The photon energy is independent of the intensity of radiations. All the photons emitted from a source of radiations travel through space with the same speed c. The frequency of photon gives the radiation, a definite energy (or colour) which does not change when photon travels through different media. Photons are not deflected by electric and magnetic fields. This shows that photons are electrically neutral.
(i) Which one among the following shows particle nature of light?

(a) Photoelectric effect (b) Interference (c) Refraction (d) Polarization

(ii) Which of the following statements about photon is incorrect?

(a) Photons exert no pressure (b) Momentum of photon is \(\frac{h v}{c}\)

(c) Rest mass of photon is zero (d) Energy of photon is hv

(iii) The rest mass of photon is

\(\text { (a) } \frac{h v}{c}\) \(\text { (b) } \frac{h v}{c^{2}}\) \(\text { (c) } \frac{h v}{\lambda}\) (d) zero

(iv) In a photon-particle collision (such as photon-electron collision), which of the following may not be conserved?

(a) Total energy (b) Number of photons (c) Total momentum (d) Both (a) and (b)

(v) 'n' photons of wavelengt '\(\lambda\)' are absorbed by a black body of mass 'm'. The momentum gained by the body is

\(\text { (a) } \frac{h}{m \lambda}\) \(\text { (b) } \frac{m n h}{\lambda}\) \(\text { (c) } \frac{n h}{m \lambda}\) \(\text { (d) } \frac{n h}{\lambda}\)

5)

To study photoelectric effect, an emitting electrode C of a photosensitive material is kept at negative potential and collecting electrode A is kept at positive potential in an evacuated tube. When light of sufficiently high frequency falls on emitting electrode, photoelectrons are emitted which travel directly to collecting electrode and hence an electric cusrent called photoelectric current starts flowing in the circuit, which is directly proportional to the number of photoelectrons emitted by emitting electrode C.

While demonstrating the existence of electromagnetic waves, Hertz found that high voltage sparks passed across the metal electrodes of the detector loop more easily when the cathode was illuminated by ultraviolet light from an arc lamp. The ultraviolet light falling on the metal surface caused the emission of negatively charged particles,which are now known to be electrons, into the surrounding space and hence enhanced the high voltage sparks.
(i) Cathode rays were discovered by

(a) Maxwell Clerk James	(b) Heinrich Hertz
(c) William Crookes	(d) J. J. Thomson

(ii) Cathode rays consists of

(a) photons

(b) electrons

(c) pistons

(d) a-particles.

(iii) Who discovered the charge on an electron for the frist time?

(a) Millikan

(b) Thomson

(c) Kelvin

(d) Coulomb

(iv) The dual nature of light is exhibited by

(a) diffraction and photoelectric effect	(b) photoelectric effect
(c) refraction and interference	(d) diffraction and reflection

(v) In the phenomenon of electric discharge through gases at low pressure, the coloured glow in the tube appears as a result of

(a) collisions between the charged particles emitted from the cathode and the atoms of the gas

(b) collision between different electrons of the atoms of the gas

(c) excitation of electrons in the atoms

(d) collision between the atoms of the gas.

CBSE 12th Standard Physics Subject Wave Optics Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
Consider the situation shown in figure. The two slits S₁ and S₂ placed symmetrically around the central line are illuminated by monochromatic light of wavelength \(\lambda\). The separation between the slits is d. The light transmitted. by the slits falls on a screen S₀ place at a distance D from the slits. The slits S₃ is at the central line and the slit S₄ is at a distance from S₃. Another screen S_c is placed a further distance D away from S_c.

(i) Find the path difference if \(z=\frac{\lambda D}{2 d}\)

\((a) \lambda\) \((b) \lambda / 2\) \((c) 3 / 2 \lambda\) \((d) 2 \lambda\)

(ii) Find the ratio of the maximum to minimum intensity observed on \(S_{c} \text { if } z=\frac{\lambda D}{d}\)

(a) 4 (b) 2 (c) \(\infty\) (d) 1

(iii) Two coherent point sources S₁ and S₂ are separated by a small distance d as shown in figure. The fringes obtained on the screen will be

(a) Concentric Circles

(b) points

(c) Straight lines

(d) semi-circles

(iv) In the case of light waves from two coherent sources S₁ and S₂. there will be constructive interference at an arbitrary point P, if the path difference S₁P - S₂P is

\(\text { (a) }\left(n+\frac{1}{2}\right) \lambda \) \( \text { (b) } n \lambda\) \( \text { (c) }\left(n-\frac{1}{2}\right) \lambda\) \( \text { (d) } \frac{\lambda}{2}\)

(v) Two monochromatic light waves of amplitudes 3A and 2A interfering at a point have a phase difference of 60°. The intensity at that point will be proportional to

(a) 5A² (b) 13A² (c) 7A² (d) 19A²

2)

Wavefront is a locus of points which vibratic in same phase. A ray of light is perpendicular to the wavefront. According to Huygens principle, each point of the wavefront is the source of a secondary disturbance and the wavelets connecting from these points spread out in all directions with the speed of wave. The figure shows a surface XY separating two transparent media, medium-1 and medium-2. The lines ab and cd represent wavefronts of a light wave travelling in medium- 1 and incident on XY. The lines ef and gh represent wavefronts of the light wave in medium -2 after refraction.

(i) Light travels as a

(a) parallel beam in each medium	(b) convergent beam in each medium
(c) divergent beam in each medium	(d) divergent beam in one medium and convergent beam in the other medium.

(ii) The phases of the light wave at c, d, e and f are \(\phi_{c}, \phi_{d}, \phi_{e}\) and \( \phi_{f}\) respectively. It is given that \(\phi_{c} \neq \phi_{f}\)

\(\text { (a) } \phi_{c} \text { cannot be equal to } \phi_{d}\)	\(\text { (b) } \phi_{d} \text { can be equal to } \phi_{e}\)
\(\text { (c) }\left(\phi_{d}-\phi_{f}\right) \text { is equal to }\left(\phi_{c}-\phi_{e}\right)\)	\(\text { (d) }\left(\phi_{d}-\phi_{c}\right) \text { is not equal to }\left(\phi_{f}-\phi_{e}\right)\)

(iii) Wavefront is the locus of all points, where the particles of the medium vibrate with the same

(a) phase

(b) amplitude

(c) frequency

(d) period

(iv) A point source that emits waves uniformly in all directions, produces wavefronts that are

(a) spherical

(b) elliptical

(c) cylindrical

(d) planar

(v) What are the types of wavefronts ?

(a) Spherical

(b) Cylindrical

(c) Plane

(d) All of these

3)

Huygen's principle is the basis of wave theory of light. Each point on a wavefront acts as a fresh source of new disturbance, called secondary waves or wavelets. The secondary wavelets spread out in all directions with the speed light in the given medium.An initially parallel cylindrical beam travels in a medium of refractive index \(\mu(I)=\mu_{0}+\mu_{2} I\), where \(\mu_{0} \text { and } \mu_{2}\)are positive constants and I is the intensity of the light beam. The intensity of the beam is decreasing with increasing radius.

(i) The initial shape of the wavefront of the beam is

(a) planar	(b) convex
(c) concave	(d) convex near the axis and concave near the periphery

(ii) According to Huygens Principle, the surface of constant phase is

(a) called an optical ray	(b) called a wave
(c) called a wavefront	(d) always linear in shape

(iii) As the beam enters the medium, it will

(a) travel as a cylindrical beam	(b) diverge
(c) converge	(d) diverge near tile axis and converge near the periphery.

(iv) Two plane wavefronts of ligbt, one incident on a thin convex lens and another on the refracting face of a thin prism. After refraction at them, the emerging wavefronts respectively become

(a) plane wavefront and plane wavefront	(b) plane wavefront and spherical wavefront
(c) spherical wavefront and plane wavefront	(d) spherical wavefront and spherical wavefront

(v) Which of the following phenomena support the wave theory of light?
1. Scattering
2. Interference
3. Diffraction
4. Velocity of light in a denser medium is less than the velocity of light in the rarer medium

(a) 1,2,3

(b) 1,2,4

(c) 2,3,4

(d) 1,3,4

4)

The phenomenon of bending of light around the sharp corners and the spreading of light within the geometrical shadow of the opaque obstacles is called diffraction of light. The light thus deviates from its linear path. The deviation becomes much more pronounced, when the dimensions of the aperture or the obstacle are comparable to the wavelength of light.

(i) Light seems to propagate in rectilinear path because

(a) its spread is very large

(b) its wavelength is very small

(c) reflected from the upper surface of atmosphere

(c) it is not absorbed by atmosphere

(ii) In diffraction from a single slit the angular width of the central maxima does not depends on

(a) \(\lambda\) of light used	(b) width of slit
(c) distance of slits from the screen	(d) ratio of \(\lambda\) and slit width

(iii) For a diffraction from a single slit, the intensity of the central point is

(a) infinite

(b) finite and same magnitude as the surrounding maxima

(c) finite but much larger than the surrounding maxima

(d) finite and substantially smaller than the surrounding maxima

(iv) .Resolving power of telescope increases when

(a) wavelength of light decreases	(b) wavelength of light increases
(c) focal length of eye-piece increases	(d) focal length of eye-piece decreases

(v) In a single diffraction pattern observed on a screen placed at D metre distance from the slit of width d metre, the ratio of the width of the ce,ntral maxima to the width of other secondary maxima is

(a) 2: 1

(b) 1: 2

(c) 1: 1

(d) 3: 1

5)
Interference is based on the superposition principle. According to this principle, at a particular point in the medium, the resultant displacement produced by a number of waves is the vector sum of the displacements produced by each of the waves. If two sodium lamps illuminate two pinholes S₁ and S₂. The intensities will add up and no interference fringes will be observed on the screen. Here the source undergoes abrupt phase change in times of the order of 10^-10 seconds.

(i) Two coherent sources of intensity 10 W/m²and 25 W/m² interfere to form fringes. Find the ratio of maximum intensity to minimum intensity

(a) 15.54 (b) 16.78 (c) 19.72 (d) 18.39

(ii) Which of the following does not show interference?

(a) Soap bubble (b) Excessively thin film (c) A thick film (d) Wedge shaped film

(iii) In a Young's double-slit experiment, the slit separation is doubled. To maintain the same fringe spacing on the screen, the screen-to-slit distance D must be changed to

(a) 2D (b) 4D (c) D/2 (d) D/4

(iv) The maximum number of possible interference maxima for slit separation equal to twice the wavelength in Young's double-slit experiment, is

(a) infinite (b) five (c) three (d) zero

(v) The resultant amplitude of a vibrating particle by the superposition of the two waves \(y_{1}=a \sin \left[\omega t+\frac{\pi}{3}\right] \text { and } y_{2}=a \sin \omega t \text { is }\)

(a) a (b)\(\sqrt{2}\) a (c) 2a (d) \(\sqrt{3}\) a

CBSE 12th Standard Physics Subject Ray Optics and Optical Instruments Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
Refraction of light is the change in the path oflight as it passes obliquely from one transparent medium to another medium. According to law of refraction \(\frac{\sin i}{\sin r}={ }^{1} \mu_{2}\) where \({ }^{1} \mu_{2}\) is called refractive index of second medium with respect to first medium. From refraction at a convex spherical surface, we have \(\frac{\mu_{2}}{v}-\frac{\mu_{1}}{u}=\frac{\mu_{2}-\mu_{1}}{R}\) Similarly from refraction at a concave spherical surface when object lies in the rarer medium, we have \(\frac{\mu_{2}}{v}-\frac{\mu_{1}}{u}=\frac{\mu_{2}-\mu_{1}}{R}\) and when object lies in the denser medium, we have \(\frac{\mu_{1}}{v}-\frac{\mu_{2}}{u}=\frac{\mu_{1}-\mu_{2}}{R}\).
(i) Refractive index of a medium depends upon

(a) nature of the medium (b) wavelength of the light used

(c) temperature (d) all of these

(ii) A ray of light of frequency 5 x 10¹⁴Hz is passed through a liquid. The wavelength of light measured inside the liquid is found to be 450 x 10^-9 m. The refractive index of the liquid is

(a) 1.33 (b) 2.52 (c) 2.22 (d) 0.75

(iii) A ray of light is incident at an angle of 60° on one face of a rectangular glass slab of refractive index 1.5. The angle of refraction is

(a) sin^-1(0.95) (b) sin^-1(0.58) (c) sin^-1(0.79) (d) sin^-1(0.86)

(iv) A point object is placed at the centre of a glass sphere of radius 6 cm and refractive index 1.5. The distance of the virtual image from the surface of sphere is

(a) 2 cm (b) 4 cm (c) 6 cm (d) 12 cm

(v) In refraction, light waves are bent on passing from one medium to the second medium because in the second medium

(a) the frequency is different (b) the co-efficient of elasticity is different

(c) the speed is different (d) the amplitude is smaller.

2)

A compound microscope is an optical instrument used for observing highly magnified images of tiny objects. Magnifying power of a compound microscope is defined as the ratio of the angle subtended at the eye by the final image to the angle subtended at the eye by the object, when both the final image and the object are situated at the least distance of distinct vision from the eye. It can be given that:\(m=m_{e} \times m_{o}\) where m_e is magnification
produced by eye lens and m_o is magnification produced by objective lens. Consider a compound microscope that consists of an objective lens of focal length 2.0 cm and an eyepiece of focal length 6.25 cm separated by a distance of 15 cm.
(i) The object distance for eye-piece, so that final image is formed at the least distance of distinct vision, will be

(a) 3.45 cm

(b) 5.cm

(c) 1.29 cm

(d) 2.59 cm

(ii) How far from the objective should an object be placed in order to obtain the condition described in part(i)?

(a) 4.5 cm

(b) 2.5 cm

(c) 1.5 cm

(d) 3.0 cm

(iii) What is the magnifying power of the microscope in case ofleast distinct vision?

(a) 20

(b) 30

(c) 40

(d) 10

(iv) The intermediate image formed by the objective of a compound microscope is

(a) real, inverted and magnified	(b) real, erect, and magnified
(c) virtual, erect and magnified	(d) virtual, inverted and magnified

(v) The magnifying power of a compound microscope increases with

(a) the focal length of objective lens is increased and that of eye lens is decreased

(b) the focal length of eye lens is increased and that of objective lens is decreased

(c) focal lengths of both objects and eye-piece are increased

(d) focal lengths of both objects and eye-piece are decreased.

3)

The lens maker's formula relates the focal length of a lens to the refractive index of the lens material and the radii of curvature of its two surfaces. This formula is called so because it is used by manufacturers to design lenses of
required focal length from a glass of given refractive index. If the object is placed at infinity, the image will be formed at focus for both double convex lens and double concave lens
Therefore, lens maker's formula is \(\frac{1}{f}=\left[\frac{\mu_{2}-\mu_{1}}{\mu_{1}}\right]\left[\frac{1}{R_{1}}-\frac{1}{R_{2}}\right]\)
When lens is placed in air, \(\mu\)₁= 1 and \(\mu\)₂ = \(\mu\). The lens maker formula takes the form \(\frac{1}{f}=(\mu-1)\left[\frac{1}{R_{1}}-\frac{1}{R_{2}}\right]\)
(i) The radius of curvature of each face of biconcave lens with refractive index 1.5 is 30 cm. The focal length of the lens in air is

(a) 12 cm

(b) 10 cm

(c) 20 cm

(d) 30 cm

(ii) The radii of curvature of the faces of a double convex lens are 10 cm and 1.5 cm. If focal length is 12 cm, then refractive index of glass is

(a) 1.5

(b) 1.78

(c) 2.0

(d) 2.52

(iii) An under-water swimmer cannot see very clearly even in absolutely clear water because of

(a) absorption oflight in water	(b) scattering of light in water
(c) reduction of speed of light in water	(d) change in the focal length of eye-lens

(iv) A thin lens of glass (\(\mu\) = 1.5) offocallength 10 cm is immersed in water (\(\mu\) = 1.33). The new focal length is

(a) 20 cm

(b) 40 cm

(c) 48 cm

(d) 12 cm

(v) An object is immersed in a fluid. In order that the object becomes invisible, it should

(a) behave as a perfect reflector

(b) absorb all light falling on it

(c) have refractive index one

(d) have refractive index exactly matching with that of the surrounding fluid.

4)
A prism is a portion of a transparent medium bounded by two plane faces inclined to each other at a suitable angle. A ray of light suffers two refractions on passing through a prism and hence deviates through a certain angle from its original path. The angle of deviation of a prism is, \(\delta\) = (\(\mu\)- 1) A, through which a ray deviates on passing through a thin prism of small refracting angle A.
If \(\mu\) is refractive index of the material of the prism, then prism formula is,\(\mu=\frac{\sin \left(A+\delta_{m}\right) / 2}{\sin A / 2}\)
(i) For which colour, angle of deviation is minimum?

(a) Red (b) Yellow (c) Violet (d) Blue

(ii) When white light moves through vacuum

(a) all colours have same speed (b) different colours have different speeds

(c) violet has more speed than red (d) red has more speed than violet.

(iii) The deviation through a prism is maximum when angle of incidence is

(a) 45° (b) 70° (c) 90° (d) 60°

(iv) What is the deviation produced by a prism of angle 6°? (Refractive index of the material of the prism is 1.644).

(a) 3.864° (b): 4.595° (c) 7.259° (d) 1.252°

(v) A ray of light falling at an angle of 50° is refracted through a prism and suffers minimum deviation. If the angle of prism is 60°, then the angle of minimum deviation is

(a) 45° (b) 75° (c) 50° (d) 40°

5)

An optical fibre is a thin tube of transparent material that allows light to pass through, without being refracted into the air or another external medium. It make use of total internal reflection. These fibres are fabricated in such a way that light reflected at one side of the inner surface strikes the other at an angle larger than critical angle. Even, if fibre is bent, light can easily travel along the length.

(i) Which of the following is based on the phenomenon of total internal reflection of light?

(a) Sparkling of diamond	(c) Instrument used by doctors for endoscopy
(b) Optical fibre communication	(d) All of these

(ii) A ray of light will undergo rotal internal reflection inside the optical fibre, if it

(a) goes from rarer medium to denser medium

(b) is incident at an angle less than the critical angle

(c) strikes the interface normally

(d) is incident at an angle greater than the critical angle

(iii) If in core, angle of incidence is equal to critical angle, then angle of refraction will be

(a) 0°

(b) 45°

(c) 90

(d) 180°

(iv) In an optical fibre (shown), correct relation for refractive indices of core and cladding is

(a) n₁ = n₂

(b) n₁ > n₂

(c) n₁ < n₂

(d) n₁ + n₂ = 2

(v) If the value of critical angle is 30° for total internal reflection from given optical fibre, then speed of light in that fibre is

(a) 3 x 108 m S^-1

(b) 1.5 x 108 m S^-1

(c) 6 x 108 m s^-1

(d) 4.5 x 108 m s^-1

CBSE 12th Standard Physics Subject Alternating Current Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
When the frequency of ac supply is such that the inductive reactance and capacitive reactance become equal, the impedance of the series LCR circuit i equal to the ohmic resistance in the circuit. Such a series LCR circuit is known as resonant series LCR circuit and the frequency of the ac supply is known as resonant frequency
Resonance phenomenon is exhibited by a circuit only ifboth Land C are present in the circuit. We cannot have resonance in a RL or RC circuit
A series LCR circuit with \(L=0.12 \mathrm{H}, C=480 \mathrm{nF}, R=23 \Omega\) is connected to a 230 V variable frequency supply

(i) Find the value of source frequency for which current amplitude is maximum

(a) 222.32 Hz (b) 550.52 Hz (c) 663.48 Hz (d) 770 Hz

(ii) The value of maximum current is

(a) 14.14 A (b) 22.52 A (c) 50.25 A (d) 47.41 A

(iii) The value of maximum power is

(a) 2200 W (b) 2299.3 W (c) 5500 W (d) 4700 W

(iv) What is the Q-factor of the given circuit?

(a) 25 (b) 42.21 (c) 35.42 (d) 21.74

(v) At resonance which of the following physical quantity is maximum?

(a) Impedance (b) Current (c) Both (a) and (b) (d) Neither (a) nor (b)

2)

An LC circuit also called a resonant circuit, tank circuit or tuned circuit is an electric circuit consisting of an inductor represented by the letter L and a capacitor, represented by the letter C connected together. An LC circuit is an idealized model since it assumes there is no dissipation of energy due to resistance.
An LC circuit contains a 20 mH inductor and a \(50 \mu \mathrm{F}\) capacitor with an initial charge of 10 mC The resistance of the circuit is negligible. Let the instant the circuit is closed be t = 0.

(i) The total energy stored initially is

(a) 5 J

(b) 3 J

(c) 10 J

(d) 1 J

(ii) The natural frequency of the circuit is

(a) 159.24 Hz

(b) 200.12 Hz

(c) 110.25 Hz

(d) 95 Hz

(iii) At what time is the energy stored completely electrical?

\(\text { (a) } T, 5 T, 9 T\)

\(\text { (b) } \frac{T}{2}, \frac{5 T}{2}, \frac{9 T}{2}\)

(c) 0, T, 2T, 3T

\(\text { (d) } 0, \frac{T}{2}, T, \frac{3 T}{2}\)

(iv) At what time is the energy stored completely magnetic?

\(\text { (a) } \frac{T}{2}, \frac{3 T}{2}, \frac{T}{4}\)

\(\text { (b) } \frac{T}{3}, \frac{T}{9}, \frac{T}{12}\)

(c) 0, 2T, 3T

\(\text { (d) } \frac{T}{4}, \frac{3 T}{4}, \frac{5 T}{4}\)

(v) The value of X_L is

\(\text { (a) } 20 \Omega\)

\(\text { (b) } 40 \Omega\)

\(\text { (c) } 60 \Omega\)

\(\text { (d) } 50 \Omega\)

3)
Step-down transformers are used to decrease or step-down voltages. These are used when voltages need to be lowered for use in homes and factories.
A small town with a demand of 800 kW of electric power at 220 V is situated 15 km away from an electric plant generating power at 440 V. The resistance of the two wire line carrying power is \(0.5 \Omega\) per km. The town gets power from the line through a 4000 - 220 V step-down transformer at a sub-station in the town.

(i) The value of total resistance of the wires is

\(\text { (a) } 25 \Omega\) \(\text { (b) } 30 \Omega\) \(\text { (c) } 35 \Omega\) \(\text { (d) } 15 \Omega\)

(ii) The line power loss in the form of heat is

(a) 550 kW (b) 650 kW (c) 600 kW (d) 700 kW

(iii) How much power must the plant supply, assuming there is negligible power loss due to leakage?

(a) 600 kW (b) 1600 kW (c) 500 W (d) 1400 kW

(iv) The voltage drop in the power line is

(a) 1700V (b) 3000V (c) 2000V (d) 2800 V

(v) The total value of voltage transmitted from the plant is

(a) 500 V (b) 4000 V (c) 3000 V (d) 7000 V
4)
In an a.c. circuit, values of voltage and current change every instant. Therefore, power of an a.c. circuit at any instant is the product of instantaneous voltage (E) and instantaneous current (I). The average power supplied to a pure resistance R over a complete cycle of a.c. is \(P=E_{v} I_{v}\) When circuit is inductive, average power per cycle is \(E_{v} I_{v} \cos \phi\)

In an a.c. circuit, 600 mH inductor and a \(50 \mu \mathrm{F}\) capacitor are connected in series with \(10 \Omega\) nresistance. The a.c. supply to the circuit is 230 V, 60 Hz.
(i) The average power transferred per cycle to resistance is

(a) 10.42 W (b) 15.25 W (c) 17.42 W (d) 13.45 W

(ii) The average power transferred per cycle to capacitor is

(a) zero (b) 10.42 W (c) 17.42 W (d) 15W

(iii) The average power transferred per cycle to inductor is

(a) 25W (b) 17.42 W (c) 16.52 W (d) zero

(iv) The total power transferred per cycle by all the three circuit elements is

(a) 17.42 W (b) 10.45W (c) 12.45 W (d) zero

(v) The electrical energy spend in running, the circuit for one hour is

(a) 7.5 x 10⁵ Joule (b) 10 x 10³ Joule (c) 9.4 x 10³ Joule (d) 6.2 x 10⁴Joule

5)

A transformer is an electrical device which is used for changing the a.c. voltages. It is based on the phenomenon of mutual induction i.e. whenever the amount of magnetic flux linked with a coil changes, an e.m.f is induced in the neighbouring coil. For. an ideal transformer, the resistances of the primary and secondary windings are negligible.

It can be shown that \(\frac{E_{s}}{E_{p}}=\frac{I_{p}}{I_{s}}=\frac{n_{s}}{n_{p}}=k\)
where the symbols have their standard meanings.
For a step up transformer \(n_{s}>n_{p} ; E_{s}>E_{p} ; k>1 ; \quad \therefore I_{s}
For a step down transformer \(n_{s}
The above relations are on the assumptions that efficiency of transformer is 100%.
lentlac ,effciency \(\eta=\frac{\text { output power }}{\text { intput power }}=\frac{E_{s} I_{s}}{E_{p} I_{p}}\)
(i) Which of the following quantity remains constant in an ideal transformer?

(a) Current

(b) Voltage

(c) Power

(d) All of these

(ii) Transformer is used to

(a) convert ac to dc voltage	(b) convert de to ac voltage
(c) obtain desired dc power	(d) obtain desired ac voltage and current

(iii) The number of turns in primary coil of a transformer is 20 and the number of turns in a secondary is 10. If the voltage across the primary is 220 ac V, what is the voltage across the secondary?

(a) 100 ac V

(b) 120 ac V

(c) 110 ac V

(d) 220 ac V

(iv) In a transformer the number of primary turns is four times that of the secondary turns. Its primary is connected to an a.c. source of voltage V. Then

(a) current through its secondary is about four times that of the current through its primary

(b) voltage across its secondary is about four times that of the voltage across its primary.

(c) voltage across its secondary is about two times that of the voltage across its primary

(d) voltage across its secondary is about \(\frac{1}{2 \sqrt{2}}\) times that of the voltage across its primary

(v) A transformer is used to light 100 W-110 V lamp from 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is

(a) 95%

(b) 99%

(c) 90%

(d) 96%

CBSE 12th Standard Physics Subject Electromagnetic Waves Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)

In an electromagnetic wave both the electric and magnetic fields are perpendicular to the direction of propagation, that is why electromagnetic waves are transverse in nature. Electromagnetic waves carry energy as they travel through space and this energy is shared equally by the electric and magnetic fields. Energy density of an electromagnetic waves is the energy in unit volume of the space through which the wave travels.
(i) The electromagnetic waves propagated perpendicular to both \(\vec{E} \text { and } \vec{B}\). The electromagnetic waves travel in the direction of

\((a) \vec{E} \cdot \vec{B}\)	\((b) \vec{E} \times \vec{B}\)
\((c) \vec{B} \cdot \vec{E}\)	\((d) \vec{B} \times \vec{E}\)

(ii) Fundame tal particle in an electromagnetic wave is

(a) photon	(b) electron
(c) phonon	(d) proton

(iii) Electromagnetic waves are transverse in nature is evident by

(a) polarisation	(b) interference
(c) reflection	(d) diffraction

(iv) For a wave propagating in a medium, identify the property that is independent of the others.

(a) velocity	(b) wavelength
(c) frequency	(d) all these depend on each other

(v) The electric and magnetic fields of an electromagnetic waves are

(a) in opposite phase and perpendicular to each other

(b) in opposite phase and parallel to each other

(c) in phase and perpendicular to each other

(d) in phase and parallel to each other.

2)

Maxwell showed that the speed of an electromagnetic wave depends on the permeability and permittivity of the medium through which it travels. The speed of an electromagnetic wave in free space is given by \(c=\frac{1}{\sqrt{\mu_{0} \varepsilon_{0}}} .\)The fact led Maxwell to predict that light is an electromagnetic wave. The emergence of the speed of light from purely electromagnetic considerations is the crowning achievement of Maxwell's electromagnetic theory. The speed of an electromagnetic wave in any medium of permeability \(\mu\) and permittivity \(\varepsilon\) will be \(\frac{c}{\sqrt{K \mu_{r}}}\) where K is the dielectric constant of the medium and \(\mu_r\) is the relative permeability.
(i) The dimensions of \(\frac{1}{2} \varepsilon_{0} E^{2}\) (\(\varepsilon_o\) permittivity of free space; E = electric field) is

\((a) \mathrm{MLT}^{-1}\)

\((b) \mathrm{ML}^{2} \mathrm{~T}^{-2}\)

\((c) \mathrm{ML}^{-1} \mathrm{~T}^{-2}\)

\((d) M L^{2} T^{-1}\)

(ii) Let [\(\varepsilon\)₀] denote the dimensional formula of the permittivity of the vacuum. If M = mass, L = length, T = time and A = electric current, then

\((a) \left[\varepsilon_{0}\right]=\mathrm{M}^{-1} \mathrm{~L}^{-3} \mathrm{~T}^{2} \mathrm{~A}\)	\((b) \left[\varepsilon_{0}\right]=M^{-1} L^{-3} T^{4} A^{2}\)
\((c) \left[\varepsilon_{0}\right]=\mathrm{MLT}^{-2} \mathrm{~A}^{-2}\)	\((d) \left[\varepsilon_{0}\right]=\mathrm{ML}^{2} \mathrm{~T}^{-1}\)

(iii) An electromagnetic wave of frequency 3MHz passes from vacuum into a dielectric medium with permittivity \(\varepsilon\) = 4. Then

(a) wavelength and frequency both remain unchanged

(b) wavelength is doubled and the frequency remains unchanged

(c) wavelength is doubled and the frequency becomes half

(d) wavelength is halved and the frequency remains unchanged.

(iv) Which of the following are not electromagnetic waves?

(a) cosmic rays

(b) \(\Upsilon\)-rays

(c) \(\beta\)-rays

(d) X-rays

(v) The electromagnetic waves travel with

(a) the same speed in all media

(b) the speed of light c = 3 x 10⁸ m s^-1 in free space

(c) the speed oflight c = 3 x 10⁸ m S^-1 in solid medium

(d) the speed of light c = 3 x 10⁸ m s^-1 in fluid medium

3)
An electromagnetic wave transports linear momentum as it travels through space. If an electromagnetic wave transfers a total energy U to a surface in time t, then total linear momentum delivered to the surface is \(p=\frac{U}{c}\) When an electromagnetic wave falls on a surface, it exerts pressure on the surface. In 1903, the American scientists Nichols and Hull succeeded in measuring radiation pressures of visible light where other had failed, by making a detailed empirical analysis of the ubiquitous gas heating and ballistic effects.
(i) The pressure exerted by an electromagnetic wave of intensity I (W m^-2) on a non-reflecting surface is (c is the velocity of light)

(a) Ic (b) Ic² (c) I/c (d) I/c²

(ii) Light with an energy flux of 18 W/cm² falls on a non-reflecting surface at normal incidence. The pressure exerted on the surface is

(a) 2 N/m² (b) 2 x 10^-4 N/m²

(c) 6 N/m² (d) 6 x 10^-4 N/m²

(iii) Radiation of intensity 0.5 W m^-2 are striking a metal plate. The pressure on the plate is

(a) 0.166 x 10^-8 N m^-2 (b) 0.212 x 10^-8 N m^-2

(c) 0.132 x 10^-8 N m^-2 (d) 0.083 x 10^-8 N m^-2

(iv) A point source of electromagnetic radiation has an average power output of 1500 W The maximum value of electric field at a distance of3 m from this source (in V m^-1) is

(a) 500 (b) 100 \(\text { (c) } \frac{500}{3}\) \(\text { (c) } \frac{250}{3}\)

(v) The radiation pressure of the visible light is of the order of

(a) 10^-2 N m² (b) 10^-4N/m (c) 10^-6 N/m² (d) 10^-8N

4)

All the known radiations from a big family of electromagnetic waves which stretch over a large range of wavelengths. Electromagnetic wave include radio waves, microwaves, visible light waves, infrared rays, UV rays, X-rays and gamma rays. The orderly distribution of the electromagnetic waves in accordance with their wavelength or frequency into distinct groups having widely differing properties is electromagnetic spectrum.
(i) Which wavelength of the Sun is used finally as electric energy?

(a) radio waves	(b) infrared waves
(c) visible light	(d) microwaves

(ii) Which of the following electromagnetic radiations have the longest wavelength?

(a) X-rays	(b) \(\Upsilon\)-rays
(c) microwaves	(d) radiowaves

(iii) Which one of the following is not electromagnetic in nature?

(a) X-rays	(b) gamma rays
(c) cathode rays	(d) infrared rays

(iv) Which of the following has minimum wavelength?

(a) X-rays	(b) ultraviolet rays
(c) \(\Upsilon\)-rays	(d) cosmic rays

(v) The decreasing order of wavelength of infrared, microwave, ultraviolet and gamma rays is

(a) microwave, infrared, ultraviolet, gamma rays

(b) gamma rays, ultraviolet, infrared, microwave

(c) microwave, gamma rays, infrared, ultraviolet

(d) infrared, microwave, ultraviolet, gamma rays

5)

Electrons oscillating in a circuit give rise to radiowaves. A transmitting antenna radiates most effectively the radiowaves of wavelength equal to the size of the antenna. The infrared waves incident on a substance set into oscillation all its electrons, atoms and molecules. This increases the internal energy and hence the temperature of the substance.
(i) If v_g, v_x and vm are the speeds of gamma rays, X-rays and microwaves respectively in vacuum, then

(a) V_g > V_X > V_m

(b) V_g X m

(c) V_g > V_X > V_m

(d) V_g= V_X= V_m

(ii) Which of the following will deflect in electric field?

(a) X-rays

(b) \(\Upsilon\)-rays

(c) cathode rays

(d) ultraviolet rays

(iii) \(\Upsilon\)-rays are detected by

(a) point contact diodes

(b) thermopiles

(c) ionization chamber

(d) photocells

(iv) The frequency of electromagnetic wave, which best suited to observe a particle of radius 3 x 10^-4 cm is the order of

(a) 10¹⁵Hz

(b) 10¹⁴Hz

(c) 10¹³Hz

(d) 10¹²Hz

(v) We consider the radiation emitted by the human body. Which one of the following statements is true?

(a) The radiation emitted is in the infrared region. .	(b) The radiation is emitted only during the day.
(c) The radiation is emitted during the summers and absorbed during the winters	(d) The radiation emitted lies in the ultraviolet region and hence it is not visible

CBSE 12th Standard Physics Subject Electromagnetic Induction Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)

Lenz's law states that the direction of induced current in a circuit is such that it opposes the change which produces it. Thus, if the magnetic flux linked with a closed circuit increases, the induced current flows in such a direction that magnetic flux is created in the opposite direction of the original magnetic flux. If the magnetic flux linked with the closed circuit decreases, the induced current flows in such a direction so as to create magnetic flux in the direction of the original flux.

(i) Which of the following statements is correct?

(a) The induced e.m.f is not in the direction opposing the change in magnetic flux so as to oppose the cause which produces it.

(b) The relative motion between the coil and magnet produces change in magnetic flux.

(c) Emf is induced only if the magnet is moved towards coil.

(d) Emf is induced only if the coil is moved towards magnet

(ii) The polarity of induced emf is given by

(a) Ampere's circuital law	(b) Biot-Savart law
(c) Lenz's law	(d) Fleming's right hand rule

(iii) Lenz's law is a consequence of the law of conservation of

(a) charge

(b) mass

(c) momentum

(d) energy

(iv) Near a circular loop of conducting wire as shown in the figure, an electron moves along a straight line. The direction of the induced current if any in the loop is

(a) variable	(b) clockwise
(c) anticlockwise	(d) zero

(v) Two identical circular coils A and B are kept in a horizontal tube side by side without touching each other. If the current in coil A increases with time, in response, the coil B.

(a) is attracted by A	(c) is repelled
(c) is repelled	(d) rotates

2)

Mutual inductance is the phenomenon of inducing emf in a coil, due to a change of current in the neighbouring coil. The amount of mutual inductance that links one coil to another depends very much on the relative positioning of the two coils, their geometry and relative separation between them. Mutual inductance between the two coils increases \(\mu_{r}\) times if the coils are wound over an iron core of relative permeability \(\mu_{r}\).

(I) A short solenoid of radius a, number of turns per unit length nI' and length L is kept coaxially inside a very long solenoid of radius b, numbdr of turns per unit length n₂• What is the mutual inductance of the system?

\(\text { (a) } \mu_{0} \pi b^{2} n_{1} n_{2} L\)

\(\text { (b) } \mu_{0} \pi a^{2} n_{1} n_{2} L^{2}\)

\(\text { (c) } \mu_{0} \pi a^{2} n_{1} n_{2} L\)

\(\text { (d) } \mu_{0} \pi b^{2} n_{1} n_{2} L^{2}\)

(ii) If a change in current of 0.01 A in one coil produces a change in magnetic flux of 2 x l0^-2 weber in another coil, then the mutual inductance between coils is

(a) 0

(b) 0.5 H

(c) 2 H

(d) 3 H

(iii) Mutual inductance of two coils can be increased by

(a) decreasing the number of turns in the coils

(b) increasing the number of turns in the coils

(c) winding the coils on wooden cores

(d) none of these

(iv) When a sheet of iron is placed in between the two co-axial coils, then the mutual inductance between the coils will

(a) increase	(b) decrease
(c) remains same	(d) cannot be predicted

(v) The SI unit of mutual inductance is

(a) ohm

(b) mho

(c) henry

(d) none of these

3)

Currents can be induced not only in conducting coils, but also in conducting sheets or blocks. Current is induced in solid metallic masses when the magnetic flux threading through them changes. Such currents flow in the form of irregularly shaped loops throughout the body of the metal. These currents look like eddies or whirlpools in water so they are known as eddy currents. Eddy currents have both undesirable effects and practically useful applications. For example it causes unnecessary heating and wastage of power in electric motors, dynamos and in the cores of transformers.
(I) The working of speedometers of trains is based on

(a) wattless currents	(b) eddy currents
(c) alternating currents	(d) pulsating currents

(ii) Identify the wrong statement

(a) Eddy currents are produced in a steady magnetic field

(b) Induction furnace uses eddy currents to produce heat.

(c) Eddy currents can be used to produce braking force in moving trains

(d) Power meters work on the principle of eddy currents.

(iii) Which of the following is the best method to reduce eddy currents?

(a) Laminating core	(b) Using thick wires
(c) By reducing hysteresis loss	(d) None ofthese

(iv) The direction of eddy currents is given by

(a) Fleming's left hand rule	(b) Biot-Savart law
(c) Lenz's law	(d) Ampere-circuital law

(v) Eddy currents can be used to heat localised tissues of the human body. This branch of medical therapy is called

(a) Hyperthermia	(b) Diathermy
(c) Inductothermy	(d) none of these

4)

In year 1820 Oersted discovered the magnetic effect of current. Faraday gave the thought that reverse of this phenomenon is also possible i.e., current can also be produced by magnetic field. Faraday showed that when we move a magnet towards the coil which is connected by a sensitive galvanometer. The galvanometer gives instantaneous deflection showing that there is an electric current in the loop.
Whenever relative motion between coil and magnet takes place an emf induced in coil. If coil is in closed circuit then current is also induced in the circuit. This phenomenon is called electromagnetic induction.

(I) The north pole of a long bar magnet was pushed slowly into a short solenoid connected to a galvanometer. The magnet was held stationary for a few seconds with the north pole in the middle of the solenoid and then withdrawn rapidly. The maximum deflection of the galvanometer was observed when the magnet was

(a) moving towards the solenoid	(b) moving into the solenoid
(c) at rest inside the solenoid	(d) moving out of the solenoid.

(ii) Two similar circular loops carry equal currents in the same direction. On moving the coils further apart, the electric current will

(a) remain unaltered	(b) increases in one and decreases in the second
(c) increase in both	(d) decrease in both

(iii) A closed iron ring is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring. The acceleration of the falling magnet is

(a) equal to g

(b) less than g

(c) more than g

(d) depends on the diameter of the ring and length of magnet

(iv) Whenever there is a relative motion between a coil and a magnet, the magnitude of induced emf set up in the coil does not depend upon the

(a) relative speed between the coil and magnet	(b) magnetic moment of the coil
(c) resistance of the coil	(d) number of turns in the coil

(v) A coil of metal wire is kept stationary in a non-uniform magnetic field

(a) an emf and current both are induced in the coil	(b) a current but no emf is induced in the coil
(c) an emf but no current is induced in the coil	(d) neither emf nor current is induced in the coil

5)

The emf induced across the ends of a conductor due to its motion in a magnetic field is called motional emf. It is produced due to the magnetic Lorentz force acting on the free electrons of the conductor. For a circuit shown in figure, if a conductor of length I moves with velocity v in a magnetic field B perpendicular to both its length and the direction of the magnetic field, then all the induced parametres are possible in the circuit.

(i) Direction of current induced in a wire moving in a magnetic field is found using

(a) Fleming's left hand rule	(b) Fleming's right hand rule
(c) Ampere's rule	(d) Right hand clasp rule

(ii) A conducting rod of length I is moving in a transverse magnetic field of strength B with velocity v. The resistance of the rod is R. The current in the rod is

\(\text { (a) } \frac{B l v}{R}\)

(b) Blv

(c) zero

\(\text { (d) } \frac{B^{2} v^{2} l^{2}}{R}\)

(iii) A 0.1 m long conductor carrying a current of 50 A is held perpendicular to a magnetic field of 1.25 mT. The mechanical power required to move the conductor with a speed of 1 m s^-1 is

(a) 62.5 mW

(b) 625 mW

(c) 6.25 mW

(d) 12.5 mW

(iv) A bicycle generator creates 1.5 V at 15 km/hr. The EMF generated at 10 km/hr is

(a) 1.5 volts

(b) 2volts

(c) 0.5volts

(d) 1 volt

(v) The dimensional formula for emf E in MKS system will be

\(\text { (a) }\left[\mathrm{ML}^{2} \mathrm{~T}^{-3} \mathrm{~A}^{-1}\right]\)

\(\text { (b) }\left[\mathrm{ML}^{2} \mathrm{~T}^{-1} \mathrm{~A}\right]\)

\(\text { (c) }\left[\mathrm{ML}^{2} \mathrm{~A}\right]\)

\(\text { (d) }\left[\mathrm{MLT}^{-2} \mathrm{~A}^{-2}\right]\)

CBSE 12th Standard Physics Subject Current Electricity Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)
The flow of charge in a particular direction constitutes the electric current. Current is measured in Ampere. Quantitatively, electric current in a conductor across an area held perpendicular to the direction of flow of charge is defined as the amount of charge is flowing across that area per unit time.
Current density at a point in a conductor is the ratio of the current at that point in the conductor to the area of cross section of the conductor of that point.
The given figure shows a steady current flows in a metallic conductor of non uniform cross section. Current density depends inversely on area, so, here \(J_{1}>J_{2}, \text { as } A_{1}.

(i) What is the current flowing through a conductor, if one million electrons are crossing in one millisecond through a cross-section of it ?

(a) 2.5 x 10^-10 A (b) 1.6 x 10^-10 A

(c) 7.5 X 10^-9 A (d) 8.2 x 10^-11 A

(ii) SI unit of electric current is

(a) Cs (b) Ns^-2 (c) Cs^-1 C^-1s^-1

(iii) A steady current flows in a metallic conductor of non-uniform cross-section. Which of these quantities is constant along the conductor?

(a) Electric field (b) Drift velocity (c) Current (d) Current density

(iv) A constant current I is flowing along the length of a conductor of variable cross-section as shown in the figure. The quantity which does not depend upon the area of cross-section is

(a) electron density (b) current density

(c) drift velocity (d) electric field

(v) When a current of 40 A flows through a conductor of area 10 m², then the current density is

(a) 4 A/m² (b) 1 A/m² (c) 2 A/m² (d) 8 A/m²

2)

Emf of a cell is the maximum potential difference between two electrodes of the cell when no current is drawn from the cell. Internal resistance is the resistance offered by the electrolyte of a cell when the electric current flows through it. The internal resistance of a cell depends upon the following factors;
(i) distance between the electrodes
(ii) nature and temperature of the electrolyte
(iii) nature of electrodes
(iv) area of electrodes.

For a freshly prepared cell, the value of internal resistance is generally low and goes on increasing as the cell is put to more and more use. The potential difference between the two electrodes of a cell in a closed circuit is called terminal potential difference and its value is always less than the emf of the cell in a closed circuit. It can be written as V = E - Jr.
(i) The terminal potential difference of two electrodes of a cell is equal to emf of the cell when

\(\text { (a) } I \neq 0\)

(b) I=0

(c) both (a) and (b)

(d) neither (a)nor (b)

(ii) A cell of emf E and internal resistance r gives a current of 0.5 A with an external resistance of \(12 \Omega\) and a current of 0.25 A with an external resistance of \(25 \Omega\) .What is the value of internal resistance of the cell?

\(\text { (a) } 5 \Omega\)

\(\text { (b) } 1 \Omega\)

\(\text { (c) } 7 \Omega\)

\(\text { (d) } 3 \Omega\)

(iii) Choose the wrong statement.

(a) Potential difference across the terminals of a cell in a closed circuit is always less than its emf.

(b) Internal resistance of a cell decrease with the decrease in temperature of the electrolyte.

(c) Potential difference versus current graph for a cell is a straight line with a -ve slope

(d) Terminal potential difference of the cell when it is being charged is given as V = E + Ir.

(iv) An external resistance R is connected to a cell of internal resistance r, the maximum current flows in the external resistance, when

(a) R = r

(b) R < r

(c) R> r

(d) R=l/r

(v) IF external resistance connected to a cell has been increased to 5 times, the potential difference across the terminals of the cell increases from 10 V to 30 V. Then, the emf of the cell is

(a) 30 V

(b) 60V

(c) 50 V

(d) 40 V

3)
A single cell provides a feeble current. In order to get a higher current in a circuit, we often use a combination of cells A combination of cells is called a battery, Cells can be joined in series, parallel or in a mixed way.
Two cells are said to be connected in series when negative terminal of one cell is connected to positive terminal of the other cell and so on. Two cells are said to be connected in parallel if positive terminal of each cell is connected to one point and negative terminal of each cell connected to the other point. In mixed grouping of cells, a certains number of identical cells are joined in series, and all such rows are then connected in parallel with each other.

(i) To draw the maximum current from a combination of cells, how should the cells be grouped?

(a) Parallel (b) Series (c) Mixed grouping (d) Depends upon the relative values of internal and external resistances

(ii) The total emf of the cells when n identical cells each of emf e are connected in parallel is

\(\text { (a) } n \varepsilon\) \(\text { (b) } n^{2} \varepsilon\) (c) E \(\text { d) } \frac{\varepsilon}{n}\)

(iii) 4 cells each of emf 2 V and internal resistance of \(1 \Omega\) are connected in parallel to a load resistor of \(2 \Omega\). Then the current through the load resistor is

(a) 2 A (b) 1.5 A (c) 1 A (d) 0.888 A

(iv) If two cells out of n number of cells each of internal resistance 'r' are wrongly connected in series, then total resistance of the cell is

(a) 2nr (b) nr - 4r (c) nr (d) r

(v) Two identical non-ideal batteries are connected in parallel. Consider the following statements.
(i). The equivalent emf is smaller than either of the two emfs.
(ii) The equivalent internal resistance is smaller than either of the two internal resistances

(a) Both (i) and (ii) are correct. (b) (i) is correct but (ii) is wrong

(c) (ii) is correct but (i) is wrong. (d) Both (i) and (ii) are wrong.

4)

Wheatstone bridge is an arrangement of four resistances P, Q, Rand S connected as shown in the figure. Their values are so adjusted that the galvanometer G shows no deflection. The bridge is then said to be balanced when this condition is achieved happens. In the setup shown here, the points Band D are at the same potential and it can be shown that \(\frac{P}{Q}=\frac{R}{S}\)
This is called the balancing condition. If any three resistances are known, the fourth can be found.
The practical form of Wheatstone bridge is slide wire bridge or Meter bridge. Using this the unknown resistance can be determined as \(S=\left(\frac{100-l}{l}\right) \times R\) ,where I is the balancing length of the Meter bridge.
(i) In a Wheatstone bridge circuit, \(P=5 \Omega, Q=6 \Omega, R=10 \Omega\) and \(S=5 \Omega\) What is the value of additional resistance to be used in series with S, so that the bridge is balanced?

\(\text { (a) } 9 \Omega\)

\(\text { (b) } 7 \Omega\)

\(\text { (c) } 10 \Omega\)

\(\text { (d) } 5 \Omega\)

(ii) A Wheatstone bridge consisting of four arms of resistances P, Q, R, S is most sensitive when

(a) all the resistances are equal

(b) all the resistances are unequal

(c) the resistances P and Q are equal but R > > P and S > > Q

(d) the resistances P and Q are equal but R < < P and S < < Q

(iii) When a metal conductor connected to left gap of a meter bridge is heated, the balancing point

(a) shifts towards right

(b) shifts towards left

(c) remains unchanged

(d) remains at zero

(iv) The percentage error in measuring resistance with a meter bridge can be minimized by adjusting the balancing point close to

(a) 0

(b)·20cm

(c) 50cm

(d) 80cm

(v) In a meter bridge experiment, the ratio ofleft gap resistance to right gap resistance is 2 : 3. The balance point from left is

(a) 20 cm

(b) 50 cm

(c) 40 cm

(d) 60 cm

5)

Whenever an electric current is passed through a conductor, it becomes hot after some time. The phenomenon of the production of heat in a resistor by the flow of an electric current through it is called heating effect of current or Joule heating. Thus, the electrical energy supplied by the source of emf is converted into heat. In purely resistive circuit, the energy expended by the source entirely appears as heat. But if the circuit has an active element like a motor, then a part of the energy supplied by the source goes to do useful work and the rest appears as heat. Joule's law of heating form the basis of various electrical appliances such as electric bulb, electric furnace,
electric press etc.
(i) Which of the following is a correct statement?

(a) Heat produced in a conductor is independent of the current flowing

(b) Heat produced in a conductor varies inversely as the current flowing

(c) Heat produced in a conductor varies directly as the square of the current flowing

(d) Heat produced in a conductor varies inversely as the square of the current flowing

(ii) If the coil of a heater is cut to half, what would happen to heat produced?

(a) Doubled

(b) Halved

(c) Remains same

(d) Becomes four times

(iii) A 25 Wand 100 Ware joined in series and connected to the mains. Which bulbs will glow brighter?

(a) 100W	(b) 25 W
(c) both bulbs will glow brighter	(d) none will glow brighter

(iv) A rigid container with thermally insulated wall contains a coil of resistance \(100 \Omega\) carrying current 1A. Change in its internal' energy after 5 min will be

(a) 0 kJ

(b) 10 kJ

(c) 20 kJ

(d) 30 kJ

(v) The heat emitted by a bulb of 1.90W in 1 min is

(a) 100 J

(b) 1000 J

(c) 600 J

(d) 6000 J

CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)

For the various charge systems, we represent equipotential surfaces by curves and line of force by full line curves. Between any two adjacent equipotential surfaces, we assume a constant potential difference the equipotential surfaces of a single point charge are concentric spherical shells with their centres at the point charge. As the lines of force point radially outwards, so they are perpendicular to the equipotential surfaces at all points.

(i) Identify the wrong statement.

(a) Equipotential surface due to a single point charge is spherical.

(b) Equipotential surface can be constructed for dipoles too.

(c) The electric field is normal to the equipotential surface through the point.

(d) The work done to move a test charge on the equipotential surface is positive

(ii) Nature of equipotential surface for a point charge is

(a) Ellipsoid with charge at foci	(b) Sphere with charge at the centre of the sphere
(c) Sphere with charge on the surface of the sphere	(d) Plane with charge on the surface

(iii) A spherical equipotential surface is not possible

(a) inside a uniformly charged sphere	(b) for a dipole
(c) inside a spherical condenser	(d) for a point charge

(iv) The work done in carrying a charge q once round a circle of radius a with a charge Q at its centre is

\(\text { (a) } \frac{q Q}{4 \pi \varepsilon_{0} a}\)

\(\text { (b) } \frac{q Q}{4 \pi \varepsilon_{0} a^{2}}\)

\(\text { (c) } \frac{q}{4 \pi \varepsilon_{0} a}\)

(d) zero

(v) The work done to move a unit charge along an equipotential surface from P to Q

(a) must be defined as \(-\int_{P}^{Q} \vec{E} \cdot d \vec{l}\)	(b) is zero
(c) can have a non-zero value	(d) both (a) and (b) are correct

2)

This energy possessed by a system of charges by virtue of their positions. When two like charges lie infinite distance apart, their potential energy is zero because no work has to be done in moving one charge at infinite distance from the other.
In carrying a charge q from point A to point B, work done \(W=q\left(V_{A}-V_{B}\right)\). This work may appear as change in KE/PE of the charge. The potential energy of two charges q₁ and q₂ at a distance r in air is \(\frac{q_{1} q_{2}}{4 \pi \varepsilon_{0} r}\). It is measured in joule. It may be positive, negative or zero depending on the signs of q_land q₂.
(i) Calculate work done in separating two electrons form a distance of 1m to 2m in air, where e is electric charge and k is electrostatic force constant.

(a) ke²

(b) e²/2

(c) -ke²/2

(d) zero

(ii) Four equal charges q each are placed at four corners of a square of side a each. Work done in carrying a charge -q from its centre to infinity is

(a) zero

\(\text { (b) } \frac{\sqrt{2} q^{2}}{\pi \varepsilon_{0} a}\)

\(\text { (c) } \frac{\sqrt{2} q}{\pi \varepsilon_{0} a}\)

\(\text { (d) } \frac{q^{2}}{\pi \varepsilon_{0} a}\)

(iii) Two points A and B are located in diametrically opposite directions of a point charge of +2 \(\mu \mathrm{C}\) at distances 2 m and 1 m respectively from it. The potential difference between A and B is

(a) 3 x 10³V

(b) 6 x 10⁴ V

(c) -9 X 10³ V

(d) -3 x 10³ V

(iv) Two point charges A = +3 nC and B = +1 nC are placed 5 ern apart in air. The work done to move charge B towards A by 1 cm is

(a) 2.0 x 10^-7 J

(b) 1.35 x 10^-7 J

(c) 2.7 X 10^-7 J

(d) 12.1 x 10^-7 J

(v) A charge Q is placed at the origin. The electric potential due to this charge at a given point in space is V. The work done by an external force in bringing another charge q from infinity up to the point is

\(\text { (a) } \frac{V}{q}\)

(b) Vq

(c) V + q

(d) V

3)
The simplest and the most widely used capacitor is the parallel plate capacitor. It consists of two large plane parallel conducting plates, separated by a small distance.
In the outer regions above the upper plate and below the lower plate, the electric fields due to the two charged plates cancel out. The net field is zero.
In the inner region between the two capacitor plates, the electric fields due to the two charged plates add up. The net field is \(\frac{\sigma}{\varepsilon_{0}}\).

For a uniform electric field, potential difference between the plates = Electric field x distance between the plates. Capacitance of the parallel plate capacitor is, the charge required to supplied to either of the conductors of the capacitor so as to increase the potential difference between then by unit amount.
(i) A parallel plate capacitor is charged and then isolated. The effect of increasing the plate separation on charge, potential and capacitance respectively are

(a) increases, decreases, decreases (b) constant, increases, decreases

(c) constant, decreases, decreases (d) constant, decreases, increases

(ii) In a parallel plate capacitor, the capacity increases if

(a) area of the plate is decreases (b) distance between the plates increases

(c) area of the plate is increases (d) dielectric constant decreases

(iii) A parallel plate capacitor has two square plates with equal and opposite charges. The surface charge densities on the plates are \(+\sigma\) and \(-\sigma\) respectively. In the region between the plates the magnitude of the electric field is

\(\text { (a) } \frac{\sigma}{2 \varepsilon_{0}}\) \(\text { (b) } \frac{\sigma}{\varepsilon_{0}}\) (c) 0 (d) none of these.

(iv) If a parallel plate air capacitor consists of two circular plates of diameter 8 cm. At what distance should the plates be held so as to have the same capacitance as that of sphere of diameter 20 cm?

(a) 9mm (b) 4mm (c) 8mm (d) 2mm

(v) If a charge of + 2.0 x 10^-8C is placed on the positive plate and a charge of -1.0 x 10^-8 C on the negative plate of a parallel plate capacitor of capacitance 1.2 x 10^-3 \(\mu \mathrm{F}\) then the potential difference developed between the plates is

(a) 6.25 V (b) 3.0 V (c) 12.5 V (d) 25 V

4)

A dielectric slab is a substance which does not allow the flow of charges through it but permits them to exert electrostatic forces on one another.
When a dielectric slab is placed between the plates, the field E_o polarises the dielectric. This induces charge -Q_p on the upper surface and + Q_p on the lower surface of the dielectric. These induced charges set up a field E_p inside the dielectric in the opposite direction of \(\vec{E}_{0}\) as shown.

(I) In a parallel plate capacitor, the capacitance increases from \(4 \mu \mathrm{F}\) to 80\(\mu \mathrm{F}\) on introducing a dielectric medium between the plates. What is the dielectric constant of the medium?

(a) 10

(b) 20

(c) 50

(d) 100

(ii) A parallel plate capacitor with air between the plates has a capacitance of 8 pF. The separation between the plates is now reduced half and the space between them is filled with a medium of dielectric constant 5.
Calculate the value of capacitance of the capacitor in second case.

(a) 8pF

(b) 10pF

(c) 80pF

(d) 100pF

(iii) A dielectric introduced between the plates of a parallel plate condenser

(a) decreases the electric field between the plates	(b) increases the capacity of the condenser
(c) increases the charge stored in the condenser	(d) increases the capacity of the condenser

(iv) A parallel plate capacitor of capacitance 1 pF has separation between the plates is d. When the distance of separation becomes 2d and wax of dielectric constant x is inserted in it the capacitance becomes 2 pF. What is the value of x?

(a) 2

(b) 4

(c) 6

(d) 8

(v) A parallel plate capacitor having area A and separated by distance d is filled by copper plate of thickness b. The new capacity is

\(\text { (a) } \frac{\varepsilon_{0} A}{d+\frac{b}{2}}\)

\(\text { (b) } \frac{\varepsilon_{0} A}{2 d}\)

\(\text { (c) } \frac{\varepsilon_{0} A}{d-b}\)

\(\text { (d) } \frac{2 \varepsilon_{0} A}{d+\frac{b}{2}}\)

5)

A capacitor is a device to store energy. The process of charging up a capacitor involves the transferring of electric charges from its one place to another. This work done in charging the capacitor is stored as its electrical potential energy.

If q is the charge and V is the potential difference across a capacitor at any instant during its charging, then small work done in storing an additional small charge dq against the repulsion of charge q already stored on it is \(d W=V . d q=(q / C) d q\)
(i) A system of 2 capacitors of capacitance \(2 \mu \mathrm{F}\) and \(4 \mu \mathrm{F}\) is connected in series across a potential difference of 6 V. The energy stored in the system is

\(\text { (a) } 3 \mu \mathrm{J}\)

\(\text { (b) } 24 \mu \mathrm{J}\)

\(\text { (c) } 30 \mu \mathrm{J}\)

\(\text { (d) } 108 \mu \mathrm{J}\)

(ii) A capacitor of capacitance of \(10 \mu \mathrm{F}\) is charged to 10 V. The energy stored in it is

\(\text { (a) } 100 \mu \mathrm{J}\)

\(\text { (b) } 500 \mu \mathrm{J}\)

\(\text { (c) } 1000 \mu \mathrm{J}\)

\(\text { (d) } 1 \mu \mathrm{J}\)

(iii) A parallel plate air capacitor has capacity C farad, potential V volt and energy E joule. When the gap between the plates is completely filled with dielectric

(a) both V and E increase	(b) both V and E decrease
(c) V decreases, E increases	(d) V increases, E decreases

(iv) A capacitor with capacitance \(5 \mu \mathrm{F}\) is charged to \(5 \mu \mathrm{C}\). If the plates are pulled apart to reduce the capacitance to \(2 \mu \mathrm{F}\),how much work is done?

\(\text { (a) } 6.25 \times 10^{-6} \mathrm{~J}\)

\(\text { (b) } 3.75 \times 10^{-6} \mathrm{~J}\)

\(\text { (c) } 2.16 \times 10^{-6} \mathrm{~J}\)

\(\text { (d) } 2.55 \times 10^{-6} \mathrm{~J}\)

(v) A metallic sphere of radius 18 cm has been given a charge of 5 x 10^-6 C. The energy of the charged conductor is

(a) 0.2 J

(b) 0.6 J

(c) 1.2 J

(d) 2.4 J

CBSE 12th Standard Physics Subject Electric Charges And Fields Chapter Case Study Questions With Solution 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)

Coulomb's law states that the electrostatic force of attraction or repulsion acting between two stationary point charges is given by
\(F=\frac{1}{4 \pi \varepsilon_{0}} \frac{q_{1} q_{2}}{r^{2}}\)

where F denotes the force between two charges q₁ and q₂separated by a distance r in free space, E_o is a constant known as permittivity of free space. Free space is vacuum and may be taken to be air practically.
If free space is replaced by a medium, then E_o is replaced by (E_ok) or (E_oEr)where k is known as dielectric constant or relative permittivity.
(i) In coulomb's law, F = \(k \frac{q_{1} q_{2}}{r^{2}}\), then on which of the following factors does the proportionality constant k depends?

(a) Electrostatic force acting between the two charges

(b) Nature of the medium between the two charges

(c) Magnitude of the two charges

(d) Distance between the two charges

(ii) Dimensional formula for the permittivity constant E_oof free space is

\(\text { (a) }\left[\mathrm{ML}^{-3} \mathrm{~T}^{4} \mathrm{~A}^{2}\right]\)	\(\text { (b) }\left[M^{-1} L^{3} T^{2} A^{2}\right]\)
\(\text { (c) }\left[\mathrm{M}^{-1} \mathrm{~L}^{-3} \mathrm{~T}^{4} \mathrm{~A}^{2}\right]\)	\(\text { (d) }\left[M L^{-3} T^{4} A^{-2}\right]\)

(iii) The force of repulsion between two charges of 1 C each, kept 1 m apart in vaccum is

\(\text { (a) } \frac{1}{9 \times 10^{9}} \mathrm{~N}\)	\(\text { (b) }\left[M^{-1} L^{3} T^{2} A^{2}\right]\)
\(\text { (c) } 9 \times 10^{7} \mathrm{~N}\)	\(\text { (d) } \frac{1}{9 \times 10^{12}} \mathrm{~N}\)

(iv) Two identical charges repel each other with a force equal to 10 mgwt when they are 0.6 m apart in air. (g = 10 ms^-2). The value of each charge is

(a) 2 mC

(b) 2 x10^-7 mC

(c) 2 nC

(d) 2\(\mu \)C

(v) Coulomb's law for the force between electric charges most closely resembles with

(a) law of conservation of energy	(b) Newton's law of gravitation
(c) Newton's 2^nd law of motion	(d) law of conservation of charge

2)
In 1909, Robert Millikan was the first to find the charge of an electron in his now-famous oil-drop experiment. In that experiment, tiny oil drops were sprayed into a uniform electric field between a horizontal pair of oppositely charged plates. The drops were observed with a magnifying eyepiece, and the electric field was adjusted so that the upward force on some negatively charged oil drops was just sufficient to balance the downward force of gravity. That is, when suspended, upward force qE just equaled Mg. Millikan accurately measured the charges on many oil drops and found the values to be whole number multiples of 1.6 x 10^-19 C the charge of the electron. For this, he won the Nobel prize.

(i) If a drop of mass 1.08 x 10^-14kg remains stationary in an electric field of 1.68 x 10⁵ N C^-I, then the charge of this drop is

(a) 6.40 x 10^-19 C (b) 3.2 x 10^-19 C

(c) 1.6 X 10^-19 C (d) 4.8 x 10^-19 C

(ii) Extra electrons on this particular oil drop (given the presently known charge of the electron) are

(a) 4 (b) 3 (c) 5 (d) 8

(iii) A negatively charged oil drop is prevented from falling under gravity by applying a vertical electric field 100 V m^-1.If the mass of the drop is 1.6 X 10^-3 g, the number of electrons carried by the drop is (g= 10 m s^-2)

(a) 10¹⁸ (b) 10¹⁵ (c) 10¹² (d) 10⁹

(iv) The important conclusion given by Millikan's experiment about the charge is

(a) charge is never quantized (b) charge has no definite value

(c) charge is quantized (d) charge on oil drop always increases.

(v) If in Millikan's oil drop experiment, charges on drops are found to be \(8 \mu \mathrm{C}, 12 \mu \mathrm{C}, 20 \mu \mathrm{C}\) then quanta of charge is

\(\text { (a) } 8 \mu \mathrm{C}\) \(\text { (b) } 20 \mu \mathrm{C}\) \(\text { (c) } 12 \mu \mathrm{C}\) \(\text { (d) } 4 \mu \mathrm{C}\)

3)

Gauss's law and Coulomb's law, although expressed in different forms, are equivalent ways of describing the relation between charge and electric field in static conditions. Gauss's law is \(\varepsilon_{0} \phi=q_{\text {encl }}\), when
q_encl is the net charge inside an imaginary closed surface called Gaussian surface. \(\phi=\oint \vec{E} \cdot d \vec{A}\) gives the electric flux through the Gaussian surface. The two equations hold only when the net charge is in vacuum or air.

(I) If there is only one type of charge in the universe, then \((\vec{E} \rightarrow \text { Electric field, } d \vec{s} \rightarrow \text { Area vector })\)

(a) \(\oint \vec{E} \cdot d \vec{s} \neq 0\) on any surface

(b) \(\oint \vec{E} \cdot d \vec{s}\) could not be defined

(c) \(\oint \vec{E} \cdot d \vec{s}=\infty\) if charge is inside

(d) \(\oint \vec{E} \cdot d \vec{s}=0\) if charge is outside, \(\oint \vec{E} \cdot d \vec{s}=\frac{q}{\varepsilon_{0}}\) if charge is inside

(ii) What is the nature of Gaussian surface involved in Gauss law of electrostatic?

(a) Magnetic

(b) Scalar

(c) Vector

(d) Electrical

(iii) A charge 10 \(\mu \)C is placed at the centre of a hemisphere of radius R = 10 cm as shown. The electric flux through the hemisphere (in MKS units) is

(a) 20 x 10⁵

(b) 10 x 10⁵

(c) 6 x 10⁵

(d) 2 x 10⁵

(iv) The electric flux through a closed surface area S enclosing charge Q is \(\phi\). If the surface area is doubled, then the flux is

\(\text { (a) } 2 \phi\)

\(\text { (b) } \phi / 2\)

\(\text { (c) } \phi / 4\)

\(\text { (d) } \phi\)

(v) A Gaussian surface encloses a dipole. 'The electric flux through this surface is

\(\text { (a) } \frac{q}{\varepsilon_{0}}\)

\(\text { (b) } \frac{2 q}{\varepsilon_{0}}\)

\(\text { (c) } \frac{q}{2 \varepsilon_{0}}\)

(d) zero

4)
In practice, we deal with charges much greater in magnitude than the charge on an electron, so we can ignore the quantum nature of charges and imagine that the charge is spread in a region in a continuous manner. Such a charge distribution is known as continuous charge distribution. There are three types of continuous charge distribution : (i) Line charge distribution (ii) Surface charge distribution (iii) Volume charge distribution as shown in figure.

(I) Statement 1 : Gauss's law can't be used to calculate electric field near an electric dipole.
Statement 2 : Electric dipole don't have symmetrical charge distribution.

(a) Statement 1 and statement 2 are true (b) Statement 1 is false but statement 2 is true

(c) Statement 1 is true but statement 2 is false (d) Both statements are false

(ii) An electric charge of 8.85 X 10^-13 C is placed at the centre of a sphere of radius 1 m. The electric flux through the sphere is

(a) 0.2 N C^-1m² (b) 0.1 N C^-1 m² (c) 0.3 N C^-1 m² (d) 0.01 N C^-1m²

(iii) The electric field within the nucleus is generally observed to be linearly dependent on r. So,

(a) a=O \(\text { (b) } a=\frac{R}{2}\) (c) a=-R \(\text { (d) } a=\frac{2 R}{3}\)

(iv) What charge would be required to electrify a sphere of radius 25 cm so as to get a surface charge density of \(\frac{3}{\pi} \mathrm{C} \mathrm{m}^{-2} ?\)

(a) 0.75 C (b) 7.5 C (c) 75 C (d) zero

(v) The SI unit of linear charge density is

(a) Cm (b) Cm^-1 (c) C m^-2 (d) C m^-3

5)

Surface charge density is defined as charge per unit surface area of surface charge distribution. i.e., \(\sigma=\frac{d q}{d S}\) Two large. thin metal plates are parallel and close to each other. On their inner faces, the plates have surface charge densities of opposite signs having magnitude of 17.0 x 10^-22 C m^-2as shown. The intensity of electric field at a point is \(E=\frac{\sigma}{\varepsilon_{0}}\) where \(\varepsilon_{0}\) = permittivity of free space.

(i) E in the outer region of the first plate is

\(\text { (a) } 17 \times 10^{-22} \mathrm{~N} / \mathrm{C}\)

\(\text { (b) } 1.5 \times 10^{-25} \mathrm{~N} / \mathrm{C}\)

\(\text { (c) } 1.9 \times 10^{-10} \mathrm{~N} / \mathrm{C}\)

(d) zero

(ii) E in the outer region of the second plate is

\(\text { (a) } 17 \times 10^{-22} \mathrm{~N} / \mathrm{C}\)

\(\text { (b) } 1.5 \times 10^{-15} \mathrm{~N} / \mathrm{C}\)

\(\text { (c) } 1.9 \times 10^{-10} \mathrm{~N} / \mathrm{C}\)

(d) zero

(iii) E between the plates is

\(\text { (a) } 17 \times 10^{-22} \mathrm{~N} / \mathrm{C}\)

\(\text { (b) } 1.5 \times 10^{-15} \mathrm{~N} / \mathrm{C}\)

\(\text { (c) } 1.9 \times 10^{-10} \mathrm{~N} / \mathrm{C}\)

(d) zero

(iv) The ratio of E from right side of B at distances 2 cm and 4 ern, respectively is

(a) 1: 2

(b) 2: 1

(c) 1: 1

\(\text { (d) } 1: \sqrt{2}\)

(v) In order to estimate the electric field due to a thin finite plane metal plate, the Gaussian surface considered is

(a) spherical

(b) cylindrical

(c) straight line

(d) none of these

CBSE 12th Standard Physics Subject Case Study Questions - 2021 - by Sharma - Kochi - May 21, 2021 - View & Read

1)

The potential at any observation point P of a static electric field is defined as the work done by the external agent (or negative of work done by electrostatic field) in slowly bringing a unit positive point charge from infinity to the observation point. Figure shows the potential variation along the line of charges. Two point charges Q₁ and Q₂ lie along a line at a distance from each other.

(i) At which of the points 1, 2 and 3 is the electric field is zero?

(a) 1

(b) 2

(c) 3

(d) Both (a) and (b)

(ii) The signs of charges Q₁ and Q₂respectively are

(a) positive and negative	(b) negative and positive
(c) positive and positive	(d) negative and negative

(iii) Which of the two charges Q₁and Q₂is greater in magnitude?

(a) Q₂

(b) Q₁

(c) Same

(d) Can't determined

(iv) Which of the following statement is not true?

(a) Electrostatic force is a conservative force

(b) Potential energy of charge q at a point is the work done per unit charge in bringing a charge from any point to infinity

(c) When two like charges lie infinite distance apart, their potential energy is zero.

(d) Both (a) and (c).

(v) Positive and negative point charges of equal magnitude are kept at \(\left(0,0, \frac{a}{2}\right)\) and \(\left(0,0, \frac{-a}{2}\right)\) respectively.
The work done by the electric field when another positive point charge is moved from (-a, 0, 0) to (0, a, 0) is

(a) positive

(b) negative

(c) zero

(d) depends on the path connecting the initial and final positions

2)

According to Ohm's law, the current flowing through a conductor is directly proportional to the potential difference across the ends of the conductor i.e \(I \propto V \Rightarrow \frac{V}{I}=R\) where R is resistance of the conductor Electrical resistance of a conductor is the obstruction posed by the conductor to the flow of electric current through it. It depends upon length, area of cross-section, nature of material and temperature of the conductor We can write \(R \propto \frac{l}{A} \text { or } R=\rho \frac{l}{A}\) where \(\rho\) is electrical resistivity of the material of the conductor.
(i) Dimensions of electric resistance is

\(\text { (a) }\left[\mathrm{ML}^{2} \mathrm{~T}^{-2} \mathrm{~A}^{-2}\right]\)

\(\text { (b) }\left[M L^{2} T^{-3} A^{-2}\right]\)

\(\text { (c) }\left[\mathrm{M}^{-1} \mathrm{~L}^{-2} \mathrm{~T}^{-1} \mathrm{~A}\right]\)

\(\text { (d) }\left[M^{-1} L^{2} T^{2} A^{-1}\right]\)

(ii) If \(1 \mu \mathrm{A}\) current flows through a conductor when potential difference of2 volt is applied across its ends, then the resistance of the conductor is

\(\text { (a) } 2 \times 10^{6} \Omega\)

\(\text { (b) } 3 \times 10^{5} \Omega\)

\(\text { (c) } 1.5 \times 10^{5} \Omega\)

\(\text { (d) } 5 \times 10^{7} \Omega\)

(iii) Specific resistance of a wire depends upon

(a) length

(b) cross-sectional area

(c) mass

(d) none of these

(iv) The slope of the graph between potential difference and current through a conductor is

(a) a straight line	(b) curve
(c) first curve then straight line	(d) first straight line then curve

(v) The resistivity of the material of a wire 1.0 m long, 0.4 mm in diameter and having a resistance of 2.0 ohm is

\(\text { (a) } 1.57 \times 10^{-6} \Omega \mathrm{m}\)

\(\text { (b) } 5.25 \times 10^{-7} \Omega \mathrm{m}\)

\(\text { (c) } 7.12 \times 10^{-5} \Omega \mathrm{m}\)

\(\text { (d) } 2.55 \times 10^{-7} \Omega \mathrm{m}\)

3)

The path of a charged particle in magnetic field depends upon angle between velocity and magnetic field.If velocity \(\vec{v}\) is at angle \(\theta\) to \(\vec{B}\) component of velocity parallel to magnetic field \((v \cos \theta)\) remains constant and component of velocity perpendicular to magnetic field \((v \sin \theta)\) is responsible for circular motion, thus the charge particle moves in a helical path.

The plane of the circle is perpendicular to the magnetic field and the axis of the helix is parallel to the magnetic field. The charged particle. moves along helical path touching the line parallel to the magnetic field passing through the starting point after each rotation.
Radius of circular path is \(r=\frac{m v \sin \theta}{1 v_{q} B}\)
Hence the resultant path of the charged particle will be a helix, with its axis along the direction of \(\vec{B}\) as shown in figure.
(i) When a positively charged particle enters into a uniform magnetic field with uniform velocity, its trajectory can be (i) a straight line (ii) a circle (iii) a helix.

(a) (i) only	(b) (i) or (ii)
(c) (i) or (iii)	(d) anyone of (i), (ii) and (iii)

(ii) Two charged particles A and B having the same charge, mass and speed enter into a magnetic field in such a way that the initial path of A makes an angle of 30° and that of B makes an angle of 90° with the field. Then the trajectory of

(a) B will have smaller radius of curvature than that of A

(b) both will have the same curvature

(c) A will have smaller radius of curvature than that of B

(d) both will move along the direction of their original velocities.

(iii) An electron having momentum 2.4 x 10^-23kg m/ s enters a region of uniform magnetic field of 0.15 T. The field vector makes an angle of 30° with the initial velocity vector of the electron. The radius of the helical path of the electron in the field shall be

(a) 2 mm

(b) 1 mm

\(\text { (c) } \frac{\sqrt{3}}{2} \mathrm{~mm}\)

(d) 0.5 mm

(iv) The magnetic field in a certain region of space is given by \(\vec{B}=8.35 \times 10^{-2} \hat{i}\) T. A proton is shot into the field with velocity \(\vec{v}=\left(2 \times 10^{5} \hat{i}+4 \times 10^{5} \hat{j}\right) \mathrm{m} / \mathrm{s}\) The proton follows a helical path in the field. The distance moved by proton in the x-direction during the period of one revolution in the yz-plane will be
(Mass of proton = 1.67 x 10^-27kg)

(a) 0.053 m

(b) 0.136 m

(c) 0.157 m

(d) 0.236 m

(v) The frequency of revolution of the particle is

\(\text { (a) } \frac{m}{q B}\)

\(\text { (b) } \cdot \frac{q B}{2 \pi m}\)

\(\text { (c) } \frac{2 \pi R}{v \cos \theta}\)

\(\text { (d) } \frac{2 \pi R}{v \sin \theta}\)

4)

Moving coil galvanometer operates on Permanent Magnet Moving Coil (PMMC) mechanism and was designed by the scientist D'arsonval.
Moving coil galvanometers are of two types
(i) Suspended coil
(ii) Pivoted coil type or tangent galvanometer.
Its working is based on the fact that when a current carrying coil is placed in a magnetic field, it experiences a torque. This torque tends to rotate the coil about its axis of suspension in such a way that the magnetic flux passing through the coil is maximum.

(i) A moving coil galvanometer is an instrument which

(a) is used to measure emf

(b) is used to measure potential difference

(c) is used to measure resistance

(d) is a deflection instrument which gives a deflection when a current flows through its coil

(ii) To make the field radial in a moving coil galvanometer

(a) number of turns of coil is kept small	(b) magnet is taken in the form of horse-shoe
(c) poles are of very strong magnets	(d) poles are cylindrically cut

(iii) The deflection in a moving coil galvanometer is

(a) directly proportional to torsional constant of spring

(b) directly proportional to the number of turns in the coil

(c) inversely proportional to the area of the coil

(d) inversely proportional to the current in the coil

(iv) In a moving coil galvanometer, having a coil of N-turns of area A and carrying current I is placed in a radial field of strength B.
The torque acting on the coil is

\(\text { (a) } N A^{2} B^{2} I\)

\(\text { (b) } N A B I^{2}\)

\(\text { (c) } N^{2} A B I\)

(d) NABI

(v) To increase the current sensitivity of a moving coil galvanometer, we should decrease

(a) strength of magnet	(b) torsional constant of spring
(c) number ofturns in coil	(d) area of coil

5)

A solenoid is a long coil of wire tightly wound in the helical form. Solenoid consists of closely stacked rings electrically insulated from each other wrapped around a non-conducting cylinder.
Figure below shows the magnetic field lines of a solenoid carrying a steady current 1.We see that if the turns are closely spaced, the resulting magnetic field inside the solenoid becomes fairly uniform, provided that the length of the solenoid is much greater than its diameter, For an "ideal" solenoid, which is infinitely long with turns tightly packed, the magnetic field inside the solenoid is uniform and parallel to the axis, and vanishes outside the solenoid.

(i) Along solenoid has 800 turns per metre length of solenoid. A current of 1.6A flows through it. The magnetic induction at the end of the solenoid on its axis is

(a) 16 x 10^-4 T

(b) 8 x 10^-4T

(c) 32 X 10^-4 T

(d) 4 x 10^-4 T

(ii) Choose the correct statement in the following

(a) The magnetic field inside the solenoid is less than that of outside

(b) The magnetic field inside an ideal solenoid is not at all uniform

(c) The magnetic field at the centre, inside an ideal solenoid is atmost twice that at the ends

(d) The magnetic field at the centre, inside an ideal solenoid is almost half of that at the ends

(iii) The magnetic field (B) inside a long solenoid having n turns per unit length and carrying current I when iron core is kept in it is \(\left(\mu_{0}=\text { permeability of vacuum, } \chi=\right.\text { magnetic susceptibility) }\)

\(\text { (a) } \mu_{0} n I(1-\chi)\)

\(\text { (b) } \mu_{0} n I \chi\)

\(\text { (c) } \mu_{0} n I^{2}(1+\chi)\)

\(\text { (d) } \mu_{0} n I(1+\chi)\)

(iv) A solenoid oflength I and having n turns carries a current I is in anticlockwise direction. The magnetic field is

\(\text { (a) } \mu_{0} n I\)	\(\text { (b) } \mu_{0} \frac{n I}{l^{2}}\)
(c) along the axis of solenoid	(d) perpendicular to the axis of coil

(v) The magnitude of the magnetic field inside a long solenoid is increased by

(a) decreasing its radius	(b) decreasing the current through it
(c) increasing its area of cross-section	(d) introducing a medium of higher permeability

CBSE 12th Standard Physics Subject Case Study Questions With Solution 2021 Part - II - by Sharma - Kochi - May 21, 2021 - View & Read

1)
In 1909, Robert Millikan was the first to find the charge of an electron in his now-famous oil-drop experiment. In that experiment, tiny oil drops were sprayed into a uniform electric field between a horizontal pair of oppositely charged plates. The drops were observed with a magnifying eyepiece, and the electric field was adjusted so that the upward force on some negatively charged oil drops was just sufficient to balance the downward force of gravity. That is, when suspended, upward force qE just equaled Mg. Millikan accurately measured the charges on many oil drops and found the values to be whole number multiples of 1.6 x 10^-19 C the charge of the electron. For this, he won the Nobel prize.

(i) If a drop of mass 1.08 x 10^-14kg remains stationary in an electric field of 1.68 x 10⁵ N C^-I, then the charge of this drop is

(a) 6.40 x 10^-19 C (b) 3.2 x 10^-19 C

(c) 1.6 X 10^-19 C (d) 4.8 x 10^-19 C

(ii) Extra electrons on this particular oil drop (given the presently known charge of the electron) are

(a) 4 (b) 3 (c) 5 (d) 8

(iii) A negatively charged oil drop is prevented from falling under gravity by applying a vertical electric field 100 V m^-1.If the mass of the drop is 1.6 X 10^-3 g, the number of electrons carried by the drop is (g= 10 m s^-2)

(a) 10¹⁸ (b) 10¹⁵ (c) 10¹² (d) 10⁹

(iv) The important conclusion given by Millikan's experiment about the charge is

(a) charge is never quantized (b) charge has no definite value

(c) charge is quantized (d) charge on oil drop always increases.

(v) If in Millikan's oil drop experiment, charges on drops are found to be \(8 \mu \mathrm{C}, 12 \mu \mathrm{C}, 20 \mu \mathrm{C}\) then quanta of charge is

\(\text { (a) } 8 \mu \mathrm{C}\) \(\text { (b) } 20 \mu \mathrm{C}\) \(\text { (c) } 12 \mu \mathrm{C}\) \(\text { (d) } 4 \mu \mathrm{C}\)

2)

This energy possessed by a system of charges by virtue of their positions. When two like charges lie infinite distance apart, their potential energy is zero because no work has to be done in moving one charge at infinite distance from the other.
In carrying a charge q from point A to point B, work done \(W=q\left(V_{A}-V_{B}\right)\). This work may appear as change in KE/PE of the charge. The potential energy of two charges q₁ and q₂ at a distance r in air is \(\frac{q_{1} q_{2}}{4 \pi \varepsilon_{0} r}\). It is measured in joule. It may be positive, negative or zero depending on the signs of q_land q₂.
(i) Calculate work done in separating two electrons form a distance of 1m to 2m in air, where e is electric charge and k is electrostatic force constant.

(a) ke²

(b) e²/2

(c) -ke²/2

(d) zero

(ii) Four equal charges q each are placed at four corners of a square of side a each. Work done in carrying a charge -q from its centre to infinity is

(a) zero

\(\text { (b) } \frac{\sqrt{2} q^{2}}{\pi \varepsilon_{0} a}\)

\(\text { (c) } \frac{\sqrt{2} q}{\pi \varepsilon_{0} a}\)

\(\text { (d) } \frac{q^{2}}{\pi \varepsilon_{0} a}\)

(iii) Two points A and B are located in diametrically opposite directions of a point charge of +2 \(\mu \mathrm{C}\) at distances 2 m and 1 m respectively from it. The potential difference between A and B is

(a) 3 x 10³V

(b) 6 x 10⁴ V

(c) -9 X 10³ V

(d) -3 x 10³ V

(iv) Two point charges A = +3 nC and B = +1 nC are placed 5 ern apart in air. The work done to move charge B towards A by 1 cm is

(a) 2.0 x 10^-7 J

(b) 1.35 x 10^-7 J

(c) 2.7 X 10^-7 J

(d) 12.1 x 10^-7 J

(v) A charge Q is placed at the origin. The electric potential due to this charge at a given point in space is V. The work done by an external force in bringing another charge q from infinity up to the point is

\(\text { (a) } \frac{V}{q}\)

(b) Vq

(c) V + q

(d) V

3)

Metals have a large number of free electrons nearly 10²⁸ per cubic metre. In the absence of electric field, average terminal speed of the electrons in random motion at room temperature is of the order of 10⁵ m s^-1 When a potential difference V is applied across the two ends of a given conductor, the free electrons in the conductor experiences a force and are accelerated towards the positive end of the conductor. On their way, they suffer frequent collisions with the ions/atoms of the conductor and lose their gained kinetic energy. After each collision, the free electrons are again accelerated due to electric field, towards the positive end of the conductor and lose their gained kinetic energy in the next collision with the ions/atoms of the conductor. The average speed of the free electrons with which they drift towards the positive end of the conductor under the effect of applied electric field is called drift speed of the electrons.
(i) Magnitude of drift velocity per unit electric field is

(a) current density

(b) current

(c) resistivity

(d) mobility

(ii) The drift speed of the electrons depends on

(a) dimensions of the conductor

(b) number density of free electrons in the conductor

(c) both (a) and (b)

(d) neither (a) nor (b)

(iii) We are able to obtain fairly large currents in a conductor because

(a) the electron drift speed is usually very large

(b) the number density of free electrons is very high and this can compensate for the low values of the 6 electron drift speed and he very small magnitude of the electron charge

(c) the number density of free electrons as well as the electron drift speeds are very large and these compensate for the very small magnitude of the electron charge

(d) the very small magnitude of the electron charge has to be divided by the still smaller product of the number density and drift speed to get the electric current

(iv) Drift speed of electrons in a conductor is very small i.e., i = 10^-4 m s^-1. The Electric bulb glows immediately. When the switch is closed because

(a) drift velocity of electron increases when switch is closed

(b) electrons are accelerated towards the negative end of the conductor

(c) the drifting of electrons takes place at the entire length of the conductor

(d) the electrons of conductor move towards the positive end and protons of conductor move towards negative end of the conductor

(v) The number density offree electrons in a copper conductor is 8.5 x 10²⁸ m^-3. How long does an electron take to drift from one end of a wire 3.0 m long to its other end? The area of cross-section of the wire is 2.0 x 10^-6m² and it is carrying a current of 3.0 A.

(a) 8.1 x 10⁴ s

(b) 2.7 x 10⁴s

(c) 9 x 10³ s

(d) 3 x 10³S

4)

Various methods can be used to measure the mass of an atom. One possibility is through the use of a mass spectrometer. The basic feature of a Banbridge mass spectrometer is illustrated in figure. A particle carrying a charge +q is first sent through a velocity selector and comes out with velocity v = E/B.
The applied electric and magnetic fields satisfy the relation E = vB so that the trajectory of the particle is a straight line. Upon entering a region where a second magnetic field \(\vec{B}_{0}\) pointing into the page has been applied, the particle will move in a circular path with radius r and eventually strike the photographic plate.

(i) In mass spectrometer, the ions are sorted out in which of the following ways?

(a) By accelerating them through electric field

(b) By accelerating them through magnetic field

(c) By accelerating them through electric and magnetic field

(d) By applying a high voltage

(ii) Radius of particle in second magnetic field B_o is

\(\text { (a) } \frac{2 m v}{q E_{0}}\)

\(\text { (b) } \frac{m v}{q E_{0}}\)

\(\text { (c) } \frac{m v}{q B_{0}}\)

\(\text { (d) } \frac{2 m E_{0} v}{q B_{0}}\)

(iii) Which of the following will trace a circular trajectory wit largest radius?

(a) Proton

(b) -\(\alpha\)particle

(c) Electron

(d) A particle with charge twice and mass thrice that of electron

(iv) Mass of the particle in terms q, B_o, B,r and E is

\(\text { (b) } \frac{q B_{0} B r}{E}\)

\(\text { (c) } \frac{q B r}{E B_{0}}\)

\(\text { (d) } \frac{q B r E}{B_{0}}\)

(v) The particle comes out of velocity selector along a straight line, because

(a) electric force is less than magnetic force	(b) electric force is greater than magnetic force
(c) electric and magnetic force balance each other	(d) can't say.

5)

When the atomic dipoles are aligned partially or fully, there is a net magnetic moment in the direction of the field in any small volume of the material. The actual magnetic field inside material placed in magnetic field is the sum of the applied magnetic field and the magnetic field due to magnetisation. This field is called magnetic intensity (H).
\(H=\frac{B}{\mu_{0}}-M\)
where M is the magnetisation of the material, llo is the permittivity of vacuum and B is the total magnetic field. The measure that tells us how a magnetic material responds to an external field is given by a dimensionless quantity is appropriately called the magnetic susceptibility: for a certain class of magnetic materials, intensity of magnetisation is directly proportional to the magnetic intensity.
(i) Magnetization of a sample is

(a) volume of sample per unit magnetic moment	(b) net magnetic moment per unit volume
(c) ratio of magnetic moment and pole strength	(d) ratio of pole strength to magnetic moment

(ii) Identify the wrongly matched quantity and unit pair.

(a) Pole strength	Am
(b) Magnetic susceptibility	dimensionless number
(c) Intensity of magnetisation	A m^-1
(d) Magnetic permeability	Henry m

(iii) A bar magnet has length- 3 cm, cross-sectional area 2 cm² and magnetic moment 3 A m². The intensity of magnetisation of bar magnet is

\(\text { (a) } 2 \times 10^{5} \mathrm{~A} / \mathrm{m}\)	\(\text { (b) } 3 \times 10^{5} \mathrm{~A} / \mathrm{m}\)
\(\text { (c) } 4 \times 10^{5} \mathrm{~A} / \mathrm{m}\)	\(\text { (d) } 5 \times 10^{5} \mathrm{~A} / \mathrm{m}\)

(iv) A solenoid has core of a material with relative permeability 500 and its windings carry a current of 1 A. The number of turns of the solenoid is 500 per metre. The magnetization of the material is nearly

\(\text { (a) } 2.5 \times 10^{3} \mathrm{Am}^{-1}\)	\(\text { (b) } 2.5 \times 10^{5} \mathrm{~A} \mathrm{~m}^{-1}\)
\(\text { (c) } 2.0 \times 10^{3} \mathrm{~A} \mathrm{~m}^{-1}\)	\(\text { (d) } 2.0 \times 10^{5} \mathrm{~A} \mathrm{~m}^{-1}\)

(v) The relative permeability of iron is 6000. Its magnetic susceptibility is

(a) 5999	(b) 6001
(c) 6000 x 10^-7	(d) 6000 x 10⁷

CBSE 12th Standard Physics Subject Case Study Questions With Solution 2021 Part - I - by Sharma - Kochi - May 21, 2021 - View & Read

1)

Coulomb's law states that the electrostatic force of attraction or repulsion acting between two stationary point charges is given by
\(F=\frac{1}{4 \pi \varepsilon_{0}} \frac{q_{1} q_{2}}{r^{2}}\)

where F denotes the force between two charges q₁ and q₂separated by a distance r in free space, E_o is a constant known as permittivity of free space. Free space is vacuum and may be taken to be air practically.
If free space is replaced by a medium, then E_o is replaced by (E_ok) or (E_oEr)where k is known as dielectric constant or relative permittivity.
(i) In coulomb's law, F = \(k \frac{q_{1} q_{2}}{r^{2}}\), then on which of the following factors does the proportionality constant k depends?

(a) Electrostatic force acting between the two charges

(b) Nature of the medium between the two charges

(c) Magnitude of the two charges

(d) Distance between the two charges

(ii) Dimensional formula for the permittivity constant E_oof free space is

\(\text { (a) }\left[\mathrm{ML}^{-3} \mathrm{~T}^{4} \mathrm{~A}^{2}\right]\)	\(\text { (b) }\left[M^{-1} L^{3} T^{2} A^{2}\right]\)
\(\text { (c) }\left[\mathrm{M}^{-1} \mathrm{~L}^{-3} \mathrm{~T}^{4} \mathrm{~A}^{2}\right]\)	\(\text { (d) }\left[M L^{-3} T^{4} A^{-2}\right]\)

(iii) The force of repulsion between two charges of 1 C each, kept 1 m apart in vaccum is

\(\text { (a) } \frac{1}{9 \times 10^{9}} \mathrm{~N}\)	\(\text { (b) }\left[M^{-1} L^{3} T^{2} A^{2}\right]\)
\(\text { (c) } 9 \times 10^{7} \mathrm{~N}\)	\(\text { (d) } \frac{1}{9 \times 10^{12}} \mathrm{~N}\)

(iv) Two identical charges repel each other with a force equal to 10 mgwt when they are 0.6 m apart in air. (g = 10 ms^-2). The value of each charge is

(a) 2 mC

(b) 2 x10^-7 mC

(c) 2 nC

(d) 2\(\mu \)C

(v) Coulomb's law for the force between electric charges most closely resembles with

(a) law of conservation of energy	(b) Newton's law of gravitation
(c) Newton's 2^nd law of motion	(d) law of conservation of charge

2)

The potential at any observation point P of a static electric field is defined as the work done by the external agent (or negative of work done by electrostatic field) in slowly bringing a unit positive point charge from infinity to the observation point. Figure shows the potential variation along the line of charges. Two point charges Q₁ and Q₂ lie along a line at a distance from each other.

(i) At which of the points 1, 2 and 3 is the electric field is zero?

(a) 1

(b) 2

(c) 3

(d) Both (a) and (b)

(ii) The signs of charges Q₁ and Q₂respectively are

(a) positive and negative	(b) negative and positive
(c) positive and positive	(d) negative and negative

(iii) Which of the two charges Q₁and Q₂is greater in magnitude?

(a) Q₂

(b) Q₁

(c) Same

(d) Can't determined

(iv) Which of the following statement is not true?

(a) Electrostatic force is a conservative force

(b) Potential energy of charge q at a point is the work done per unit charge in bringing a charge from any point to infinity

(c) When two like charges lie infinite distance apart, their potential energy is zero.

(d) Both (a) and (c).

(v) Positive and negative point charges of equal magnitude are kept at \(\left(0,0, \frac{a}{2}\right)\) and \(\left(0,0, \frac{-a}{2}\right)\) respectively.
The work done by the electric field when another positive point charge is moved from (-a, 0, 0) to (0, a, 0) is

(a) positive

(b) negative

(c) zero

(d) depends on the path connecting the initial and final positions

3)

Emf of a cell is the maximum potential difference between two electrodes of the cell when no current is drawn from the cell. Internal resistance is the resistance offered by the electrolyte of a cell when the electric current flows through it. The internal resistance of a cell depends upon the following factors;
(i) distance between the electrodes
(ii) nature and temperature of the electrolyte
(iii) nature of electrodes
(iv) area of electrodes.

For a freshly prepared cell, the value of internal resistance is generally low and goes on increasing as the cell is put to more and more use. The potential difference between the two electrodes of a cell in a closed circuit is called terminal potential difference and its value is always less than the emf of the cell in a closed circuit. It can be written as V = E - Jr.
(i) The terminal potential difference of two electrodes of a cell is equal to emf of the cell when

\(\text { (a) } I \neq 0\)

(b) I=0

(c) both (a) and (b)

(d) neither (a)nor (b)

(ii) A cell of emf E and internal resistance r gives a current of 0.5 A with an external resistance of \(12 \Omega\) and a current of 0.25 A with an external resistance of \(25 \Omega\) .What is the value of internal resistance of the cell?

\(\text { (a) } 5 \Omega\)

\(\text { (b) } 1 \Omega\)

\(\text { (c) } 7 \Omega\)

\(\text { (d) } 3 \Omega\)

(iii) Choose the wrong statement.

(a) Potential difference across the terminals of a cell in a closed circuit is always less than its emf.

(b) Internal resistance of a cell decrease with the decrease in temperature of the electrolyte.

(c) Potential difference versus current graph for a cell is a straight line with a -ve slope

(d) Terminal potential difference of the cell when it is being charged is given as V = E + Ir.

(iv) An external resistance R is connected to a cell of internal resistance r, the maximum current flows in the external resistance, when

(a) R = r

(b) R < r

(c) R> r

(d) R=l/r

(v) IF external resistance connected to a cell has been increased to 5 times, the potential difference across the terminals of the cell increases from 10 V to 30 V. Then, the emf of the cell is

(a) 30 V

(b) 60V

(c) 50 V

(d) 40 V

4)

The path of a charged particle in magnetic field depends upon angle between velocity and magnetic field.If velocity \(\vec{v}\) is at angle \(\theta\) to \(\vec{B}\) component of velocity parallel to magnetic field \((v \cos \theta)\) remains constant and component of velocity perpendicular to magnetic field \((v \sin \theta)\) is responsible for circular motion, thus the charge particle moves in a helical path.

The plane of the circle is perpendicular to the magnetic field and the axis of the helix is parallel to the magnetic field. The charged particle. moves along helical path touching the line parallel to the magnetic field passing through the starting point after each rotation.
Radius of circular path is \(r=\frac{m v \sin \theta}{1 v_{q} B}\)
Hence the resultant path of the charged particle will be a helix, with its axis along the direction of \(\vec{B}\) as shown in figure.
(i) When a positively charged particle enters into a uniform magnetic field with uniform velocity, its trajectory can be (i) a straight line (ii) a circle (iii) a helix.

(a) (i) only	(b) (i) or (ii)
(c) (i) or (iii)	(d) anyone of (i), (ii) and (iii)

(ii) Two charged particles A and B having the same charge, mass and speed enter into a magnetic field in such a way that the initial path of A makes an angle of 30° and that of B makes an angle of 90° with the field. Then the trajectory of

(a) B will have smaller radius of curvature than that of A

(b) both will have the same curvature

(c) A will have smaller radius of curvature than that of B

(d) both will move along the direction of their original velocities.

(iii) An electron having momentum 2.4 x 10^-23kg m/ s enters a region of uniform magnetic field of 0.15 T. The field vector makes an angle of 30° with the initial velocity vector of the electron. The radius of the helical path of the electron in the field shall be

(a) 2 mm

(b) 1 mm

\(\text { (c) } \frac{\sqrt{3}}{2} \mathrm{~mm}\)

(d) 0.5 mm

(iv) The magnetic field in a certain region of space is given by \(\vec{B}=8.35 \times 10^{-2} \hat{i}\) T. A proton is shot into the field with velocity \(\vec{v}=\left(2 \times 10^{5} \hat{i}+4 \times 10^{5} \hat{j}\right) \mathrm{m} / \mathrm{s}\) The proton follows a helical path in the field. The distance moved by proton in the x-direction during the period of one revolution in the yz-plane will be
(Mass of proton = 1.67 x 10^-27kg)

(a) 0.053 m

(b) 0.136 m

(c) 0.157 m

(d) 0.236 m

(v) The frequency of revolution of the particle is

\(\text { (a) } \frac{m}{q B}\)

\(\text { (b) } \cdot \frac{q B}{2 \pi m}\)

\(\text { (c) } \frac{2 \pi R}{v \cos \theta}\)

\(\text { (d) } \frac{2 \pi R}{v \sin \theta}\)

5)

By analogy to Gauss's law of electrostatics, we can write Gauss's law of magnetism as \(\oint \vec{B} \cdot d \vec{s}=\mu_{0} m_{\text {inside }}\) where \(\oint \vec{B} \cdot d \vec{s}\) is the magnetic flux and \(m_{\text {inside }}\) is the net pole strength inside the closed surface.
We do not have an isolated magnetic pole in nature. At least none has been found to exist till date. The smallest unit of the source of magnetic field is a magnetic dipole where the net magnetic pole is zero. Hence, the net magnetic pole enclosed by any closed surface is always zero. Correspondingly, the flux of the magnetic field through any closed surface is zero.

(I) Consider the two idealised systems
(i) a parallel plate capacitor with large plates and small separation and
(ii) a long solenoid oflength L >> R, radius of cross-section.
In (i) \(\vec{E}\) is ideally treated as a constant between plates and zero outside. In (ii) magnetic field is constant inside the solenoid and zerq outside. These idealised assumptions, however, contradict fundamental laws as below

(a) case (i) contradicts Gauss's law for electrostatic fields

(b)case (ii) contradicts Gauss's aw for magnetic fields

\(\text { (c) case (i) agrees with } \oint \vec{E} \cdot \overrightarrow{d l}=0 \text { . }\)

\(\text { (d) case (ii) contradicts } \oint \vec{H} \cdot \overrightarrow{d l}=I_{e n}\)

(ii) The net magnetic flux through any closed surface, kept in a magnetic field is

(a) zero

\(\text { (b) } \frac{\mu_{0}}{4 \pi}\)

\(\text { (c) } 4 \pi \mu_{0}\)

\(\text { (d) } \frac{4 \mu_{0}}{\pi}\)

(iii) A closed surface S encloses a magnetic dipole of magnetic moment 2ml. The magnetic flux emerging from the surface is

\(\text { (a) } \mu_{0} m\)

(b) zero

\(\text { (c) } 2 \mu_{0} m\)

\(\text { (d) } \frac{2 m}{\mu_{0}}\)

(iv) Which of the following is not a consequence of Gauss's law?

(a) The magnetic poles always exist as unlike pairs of equal strength.

(b) If several magnetic lines of force enter in a closed surface, then an equal number of lines of force must leave that surface

(c) There are abundant sources or sinks of the magnetic field inside a closed surface

(d) Isolated magnetic poles do not exist

(v) The surface integral of a magnetic field over a surface

(a) is proportional to mass enclosed	(b) is proportional to charge enclosed
(c) is zero	(d) equal to its magnetic flux through that surface.

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1)
At a particular point, electric field depends upon
2)
The SI unit of electric field intensity is
3)
Electric field due to a single charge is
4)
Electric dipole moment is
5)
Electric field intensity (E) due to an electric dipole varies with distance (r) of the point from the centre of dipole as:

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(a) bi-directional device	(b) ohmic device
(c) non-ohmic device	(d) passive element

(a) 2(KE_max/e)	(b) (KE_max/e)
(c) (KE_max/3e)	(d) (KE_max/2e)

(a) Light emitting diode	(b) Diode
(c) Photocell	(d) Transistor

(a) unchanged	(b) halved
(c) doubled	(d) more than twice its initial value

Light	Violet	blue	Green	Yellow	Orange	Red
\(\lambda\) in \(\dot A\)	4000-5000	4500-5000	5000-5500	5500-6000	6000-6500	6500-7000

(a) should be A/2, where A is the wavelength.	(b) should be of the order of wavelength.
(c) has no relation to wavelength.	(d) should be much larger than the wavelength.

(a) 30 cm right of lens	(b) 60 ern right of lens
(c) 70 ern left of lens	(d) 40 cm left oflens

(a) converging lens	(b) diverging lens
(c) plano-converging lens	(d) plano-diverging lens

(a) at its focus F	(b) between F and 2F
(c) at 2F	(d) between F and optical centre

(a) nature of the medium	(b) wavelength of the light used
(c) temperature	(d) all of these

(a) the frequency is different	(b) the co-efficient of elasticity is different
(c) the speed is different	(d) the amplitude is smaller.

(a) all colours have same speed	(b) different colours have different speeds
(c) violet has more speed than red	(d) red has more speed than violet.

(a) 2.5 x 10^-10 A	(b) 1.6 x 10^-10 A
(c) 7.5 X 10^-9 A	(d) 8.2 x 10^-11 A

(a) electron density	(b) current density
(c) drift velocity	(d) electric field

(a) Both (i) and (ii) are correct.	(b) (i) is correct but (ii) is wrong
(c) (ii) is correct but (i) is wrong.	(d) Both (i) and (ii) are wrong.

(a) Total charge conservation	(b) Quantization of charge
(c) Two types of charge	(d) Circular line of force

(a) 5.8 x 10^-18C	(b) 3.2 x 10^-18C
(c) 4.5 x 10^-19C	(d) 8.6 x 10^-19C

(a) 6.25 x 10²⁷	(b) 1.6 x 10¹⁹
(c) 6.25 x 10²⁸	(d) 6.25 x 10⁹

(a) 6.40 x 10^-19 C	(b) 3.2 x 10^-19 C
(c) 1.6 X 10^-19 C	(d) 4.8 x 10^-19 C

(a) charge is never quantized	(b) charge has no definite value
(c) charge is quantized	(d) charge on oil drop always increases.

12th Standard stateboard question papers & Study material

தமிழ் Subjects

உயிரியல்

கணினி பயன்பாடுகள்

கணினி அறிவியல்

வணிகக் கணிதம் மற்றும் புள்ளியியல்

வணிகவியல்

பொருளியல்

கணிதவியல்

வேதியியல்

இயற்பியல்

கணினி தொழில்நுட்பம்

வரலாறு

கணக்குப்பதிவியல்

தமிழ்

English Subjects

Maths

Chemistry

Physics

Biology

Computer Science

Business Maths and Statistics

Economics

Commerce

Accountancy

History

Computer Applications

Computer Technology

English

11th Standard stateboard question papers & Study material

தமிழ் Subjects

கணிதம்

உயிரியல்

பொருளியல்

இயற்பியல்

வேதியியல்

வரலாறு

வணிகக் கணிதம் மற்றும் புள்ளியியல்

கணினி அறிவியல்

கணக்குப்பதிவியல்

வணிகவியல்

கணினி பயன்பாடுகள்

கணினி தொழில்நுட்பம்

தமிழ்

English Subjects

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Commerce

Economics

Biology

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Accountancy

Computer Science

Physics

Chemistry

Computer Applications

History

Computer Technology

தமிழ்

English

9th Standard stateboard question papers & Study material

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English Subjects

Maths

Science

Social Science

கணிதம்

அறிவியல்

சமூக அறிவியல்

6th Standard stateboard question papers & Study material

தமிழ் Subjects

கணிதம்

அறிவியல்

சமூக அறிவியல்

English Subjects

Maths

Science

Social Science

10th Standard stateboard question papers & Study material

தமிழ் Subjects

கணிதம்

(a) Statement 1 and statement 2 are true	(b) Statement 1 is false but statement 2 is true
(c) Statement 1 is true but statement 2 is false	(d) Both statements are false

(a) Diodes are uncontrolled devices.	(b) Diodes are rectifying devices.
(c) Diodes are unidirectional devices.	(d) Diodes have three terminals

(a) majority carriers	(b) minority carriers
(c) both (a) and (b)	(d) fixed donor and acceptor ions.

(a) friction	(b) elastic damping/scattering
(c) absorption	(d) none of these

(a) Both II and III	(b) Both I and III
(c) Only II	(d) Both I and II

(a) less than 1	(b) greater than 1
(c) equal to 1	(d) depends 0 the mass of parent nucleus

(a) change independent	(b) short range force
(c) non-conservative force	(d) all of these.

(a) nuclear forces	(b) van der Waal's forces
(c) tensor forces	(d) coulomb forces

(a) Photons exert no pressure	(b) Momentum of photon is \(\frac{h v}{c}\)
(c) Rest mass of photon is zero	(d) Energy of photon is hv

(a) 2 N/m²	(b) 2 x 10^-4 N/m²
(c) 6 N/m²	(d) 6 x 10^-4 N/m²