CBSE 12th Standard Physics Subject Value Based Questions 5 Mark Questions 2021 Part - II

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Questions:

Generic 5

15 x 5 = 75

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?

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?

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.

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?

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?

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?

Self- inductance is the property of a coil by virtue of which the coil oppose any change in the strength of current flowing through it by inducing an emf in itself. The induced emf is also called back emf. Self-inductance represents electric inertia which is measured in terms of coefficient of self-inductance(L). We can show that
L = \(L=\cfrac { \phi }{ I } \) = \(\cfrac { -e }{ { \triangle I }/{ \triangle t } } \)
Read the above passage and answer the following questions:
(i) How does the self-inductance of a coil represent its electric inertia?
(ii) An emf of 100\(\mu\) V is induced in a coil when the current in it changes from 5A to 1A in 0.4s.
Find the self-inductance of the coil.

Raj is in XII standard. His Physics teacher demonstrated an experiment to explain Faraday's laws of electromagnetic induction. Raj interrupted his lecture and asked, "Is there any possibility of induced emf due to the earth's magnetism"? The teacher was stunned for a moment and gave this question for group discussion. Finally, the students came out with correct answer.
(i) Write the values that you learnt from this incident.
(ii) What can be reason for Raj's question?

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?

10.

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?

11.

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?

12.

A pure semiconductor germanium or silicon,free of every impurity is called intrinsic semiconductor, At room temperature, a pure semiconductor has a very small number of current carriers (electrons and holes).Hence,its conductivity is low.
When the impurity atoms of valence five or three are doped in a pure semiconductor,we get respectively \(n-\) type or \(p-\) type extrinsic semiconductor.In case of a doped semiconductor.\({ n }_{ e }n_{ h }={ n }_{ i }^{ 2 };\)when \({ n }_{ e }\) and \(n_{ h }\) are the number density of electrons and holes respectively and \({ n }_{ i }\) is the number density of intrinsic charge carriers in a pure semiconductor. The conductivity of extrinsic semiconductor is much higher than that that of intrinsic semiconductor.
Read the above passage and answer the following question:
(i) Name two materials to be doped in pure semiconductor of silicon to get (a) \(p-\)type semiconductor (b) \(n-\)type semiconductor
(ii) What do you learn from the above study?

13.

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?

14.

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?

15.

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.

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Answers Key:

Generic 5

15 x 5 = 75

(i) Moon is a natural satellite of the earth but it is not an active satellite as it carries no electronic equipments for receiving, amplifying and transmitting the signal back to the earth. Moon cannot be used as a communication satellite because
(a) the distance between the earth and the moon is not proper.
(b) the period of revolution of the moon is not 24 hr.
(c) the moon is not revolving in the equitorial plane of the earth.
(ii) The three groups showed the values of eagerness to engage in a debate, promptness in taking decision and ability to work in a group in a constructive manner.

(i) As set up that transfer information implicitly from one point to another is called communication system. Analog signal is better than a digital signal.
(ii) Sohan is an intelligent and knowledgeable person.
(iii) There are three communication satellites.
(iv) The three groups display the values if eagerness to engage in adebate, promptness in taking decision and ability to work in a constructive manner.

(i) Concern for his brother, care about the school thorough subject knowledge.
(ii) Balmer series.
(iii) His brother has zeal to learn.

(i) Khusbhu is intelligent, cooperative and has good knowledge of electronic devices.
(ii) An integrated circuit is a small device in which different components of electronics circuits such as a diode, transistor, resistors, inductor, etc., are fabricated together in a small chip.
Since it can operate a wide range of functions simultaneously it is used in computer, television, cars, CD players, cell phones, etc.
(iii) The microprocessor is an IC that process all information in a computer.

(i) Jayant is helpful, caring and has presence of mind to deal with adverse situation.
(ii) X-ray is produced by the bombardment of a metal target by high energy electrons.
(iii) It is used in the determination of structure of solids by X-rays diffraction method.

(i) He refers to the process of dispersion of light. Dispersion of light is due to the different velocities of light rays in a medium.
(ii) Studying and analysing the spectrum of distant light sources.
(iii) Curiosity, research mindedness and awareness.

(i) On account of self-inductance, a coil opposes change in strength of current flowing through it, i.e., coil opposes the growth and decay of current through it. Thus, self-inductance is correctly representing the electric inertia of coil.
(ii) Here, e = 100 V = 10\(\mu\)0 10^-6V,
= 1 - 5 = -4A, \(\triangle\)t = 0.4s
From e = -L \(\cfrac{\triangle I}{\triangle t}\) ,we have
L = - \(\cfrac{e\times\triangle t}{\triangle I}\) = - \(\cfrac { 100\times { 10 }^{ -6 }\times 0.4 }{ -4 } \)
= 10^-5H

(i) Term spirit, curiosity.
(ii) When the wire in N-S direction is dropped freely, none of the components of the earth's magnetic field is intercepted. So, no induced emf is produced. When the wire is dropped freely in East-West direction, horizontal component of the earth's magnetic field is intercepted. So, emf is induced in the coil.

(i) Acknowledging the help from others with gratitude. Awareness of the technology, helping tendency, practical knowledge of the subject.
(ii) Vasu checked the wiring because he has practical knowledge and he can rectify the problem.
(iii) An electric fuse is a wire used as a safety device, which melts when current exceeds the limit. Fuse wire has low melting point, high resistivity

10.

As \(\tau =nIBA \ sin \ \theta ,\ therefore,\ (i) \ \tau =0, \ when \ sin\theta =0 \ or \ \theta =0°, \ i.e.\)when the plane of coil is perpendicular to the direction of magnetic field. (ii) \(\tau =\) maximum, when \(sin \ \theta \)=maximum=1 or \(\theta =90°\)
\({ \tau }_{ max }=nIBA\times 1=nIBA\)
It will be so when the plane of coil is parallel to the direction of magnetic field.
(ii) Here, n = 200; r = 0.05m; I = 2.0 A; B = 0.20 T; \(\theta =90°-60°\)=\(30°\)
\( \tau =nIBA \ sin \ \theta ,\ therefore,\ (i) \ \tau =0, \ when \ sin\theta =0 \ or \ \theta =30°-60°, \ i.e.,\)
\( \\ { \tau }_{ max }=nIBA\times 1=nIBA\)
\( \tau =nIBA \ sin \ \theta =nIB({ \pi r }^{ 2 })sin\theta =200\times 2.0\times 0.20\left[ (22/7)\times { \left( 0.05 \right) }^{ 2 } \right] \times sin30°\)
\(=0.314\quad N-m=0.31\ Nm\)
(iii) From the above study, we find that when potential energy of the coil is minimum, both force and torque acting on the coil are zero. The same is true in real life. a person who is humble and boasts of nothing, would be a happy person, with no pulls and pressure of life.

11.

(i) The force is due to the interaction between magnetic fields due to currents in two linear parallel conductors.
(ii) Here, \({ l }_{ 1 }=2cm=2\times { 10 }^{ -2 }m;{ l }_{ 2 }=20\times { 10 }^{ -2 }m;{ I }_{ 1 }=2.0A;{ I }_{ 2 }=5.0A;r=4\times { 10 }^{ -2 }m\)
Since action and reaction are equal and opposite so the magnitude of repulsive force on 20 cm long wire = the magnitude of repulsive force on 2 cm long wire
= \(\frac { { \mu }_{ 0 } }{ 4\pi } \frac { 2{ I }_{ 1 }{ I }_{ 2 } }{ r } { l }_{ 1 }={ 10 }^{ -7 }\times \frac { 2\times 2\times 5\times (2\times { 10 }^{ -2 }) }{ 4\times { 10 }^{ -2 } }\)
\( ={ 10 }^{ -6 }\)
This study shows that when the current through two parallel conductors flow in the same direction, they attract each other and vice versa. It implies that when the thoughts and actions of two business partners are aligned in the same direction, their behavior is cohesive and they succeed. If there thoughts and actions are opposing, the partnership is likely to collapse. The same thing is true for husband and wife. For a successful family life, the coherence of thoughts and action is a must.

12.

(i) (a) The doping of pure silicon with boron or aluminium will give us \(p-\)type semiconductor
(b) The doping of pure silicon with arsenic or phosphorous will give us \(n-\)type semiconductor.
(ii) From the above study, we find that to get better output current ,pure semiconductor has to be adopted with suitable (impurity) atoms.Similarly,in day to day life,the appearence of right kind of persons(leaders) in society can improve their lot.

13.

Work function of metal depends upon the amount of restraining forces acting on the electrons to be ejected.In different metals, the amount of restraining forces on the electrons to be ejected is different.Hence, work function for different metals is different.
Here,
\({ \phi }_{ 0 }=1.2eV=1.2\times 1.6\times { 10 }^{ -19 }J\)
\( As \ { \phi }_{ 0 }=\frac { hc }{ { \lambda }_{ 0 } } \ or \ { \lambda }_{ 0 }=\frac { hc }{ { \phi }_{ 0 } } =\frac { \left( 6.63\times { 10 }^{ -34 } \right) \times \left( 3\times { 10 }^{ 8 } \right) }{ 1.2\times 1.6\times { 10 }^{ -19 } } =1037\times { 10 }^{ -19 }m=1037nm\)
(iii) Work function of metal required to the minimum energy required by an electron to escape from the metal. In day-to-day life, we find that we can purchase something only when we have money, which is at least equal to or more than that price. Thus to purchase comforts of life, we have to work hard and earn money by fair means.

14.

(i) Nuclear reactors are used in electric power generation. They are also used to produce radioactive isotopes which have applications in medicine, industry and agriculture.
(ii) Radioactive waste consists of fission products and transuranic elements such as plutonium and americium. This waste is extremely hazardous to all forms of life on earth.
(iii) People often oppose the location site of a nuclear reactor because any leakage of nuclear radiations can affect adversely miles of area surrounding it. Elaborate safety measures are needed not only for reactor operations, but also for handling and disposal of radioactive waste.
I would suggest that Government must take stringent safety measures and assure people of safeguards in the event of nuclear accidents. At the same time, people must also be educated accordingly.

15.

(i) From the fission of a single nucleus of \(_{ 92 }{ { { U }^{ 235 } } }\); 200 MeV energy is released in \({ 10 }^{ -9 }\) second, i.e., almost instantly.
(ii) First atomic explosion occurred in 1945 when an atom bomb was dropped on the city of Hiroshima, Japan. This resulted in the killing of about 66000 people and grievous injury to an equal number. 2/3rd of city structures were smashed and so on.
(iii) No, the research must go on. But we must investigate ways and means for harnessing the enormous amount of nuclear energy for peaceful purposes. Nuclear reactor is an outcome of that research.