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?

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?

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? 

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?

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?

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?

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.

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?

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.

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?

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?

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?

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?