CBSE Class 12 Physics Electromagnetic Induction Important Questions

CBSE Class 12 Physics Electromagnetic Induction Important Questions. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Comprehension

Inductance of a coil or a circuit can be defined as a properly by virtue of which, the coil or circuit opposes any change in the flux linked to it. Whenever one tries to change the flux, the coil or circuit produces induced current or induced e.m.f., so that it can oppose the cause of the change of flux. It is also called electromagnetic inertia, which opposes any change in its electromagnetic state. Magnetic flux is proportional to the current (I) flowing is φ = LI, where L is proportionality constant, called self inductance.
Energy in magnetic field inside inductor can be associated as U = (1/2)LI², where L is self inductance and I is the current flowing through it.

Now answer the following
1. In the shown figure a magnet is placed along the axis of a conducting coil. If magnet is pushed towards coils

(a) coil get attracted toward magnet
(b) coil get repelled away from magnet
(c) a force on magnet acts away from coil
(d) coil behaves like magnet

2. In the shown L-R circuit switch is thrown from (1) to (2) at time t = 0

(a) Just after closing the switch current becomes half
(b) Just after closing the switch current will not change
(c) Long time after closing the switch current in the circuit is equal to E/2R
(d) Long time after closing the switch current is 2E/R

3. In the shown in the figure smooth coil having an smooth iron rod, placed as shown in the figure. Mass of rod is m and self inductance of coil L and resistance R. If force F is applied on the rod (neglecting gravity) just after the force is applied.

(a) acceleration of rod is F/m
(b) acceleration of rod is less than F/m
(c) acceleration of rod is more than F/m R
(d) none of these

Each of the questions given below consists of two statements, an assertion (A) and reason (R).
Select the number corresponding to the appropriate alternative as follows
(a) If both A and R are true and R is the correct explanation of A
(b) If both A and R are true but R is not the correct explanation of A
(c) If A is true but R is false
(d) If A is false but R is true

4. A: The oscillations of a copper disc in magnetic field are damped.
R: The eddy currents produced in the copper disc always oppose its oscillatory motion.

5. A: Self inductance is the inertia of electricity.
R: The unit of self inductance is henry.

6. A: Coefficient of mutual induction of two coils depends on their relative orientation.
R: Inductance opposes the growth of current.

7. A: The energy is stored in the inductor at the expense of the energy of the source of e.m.f.
R: The energy resides in the inductor in the form of magnetic field.

8. A. Lenz’s law violates the principle of conservation of energy.
R. Induced e.m.f. opposes always opposes magnetic flux responsible for its production.

9. A. An emf is induced between the wings of the aeroplane, when it is flying horizontally.
R. An emf is induced due to vertical component of earth’s magnetic filed.

10. A. Current takes time to become zero in Inductor Resistance circuit.
R. Current takes infinite time to grow to its maximum value in the Inductor Resistance circuit.

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