# Physics MCQs for Class 12 with Answers Chapter 6 Electromagnetic Induction

Free PDF Download of CBSE Physics Multiple Choice Questions for Class 12 with Answers Chapter 6 Electromagnetic Induction. Physics MCQs for Class 12 Chapter Wise with Answers PDF Download was Prepared Based on Latest Exam Pattern. Students can solve NCERT Class 12 Physics Electromagnetic Induction MCQs Pdf with Answers to know their preparation level.

## Electromagnetic Induction Class 12 Physics MCQs Pdf

1. Two coils are placed closed to each other. The mutual inductance of the pair of coils depends upon
(a) the rate at which currents are changing in the two coils.
(b) relative position and orientation of two coils.
(c) the material of the wires of the coils.
(d) the currents in the two coils.

Explaination:
(b) Mutual induction depends upon the relative orientation and position of coil w.r.t. each other.

2. When current in a coil changes from 5 A to 2 A in 0.1 s, average voltage of 50 V is produced. The self-inductance of the coil is
(a) 1.67 H
(b) 6 H
(c) 3 H
(d) 0.67 H

Explaination:

3. A coil having 500 sq. loops of side 10 cm is placed normal to magnetic flux which increases at a rate of 1 T/s. The induced emf is
(a) 0.1 V
(b) 0.5 V
(c) 1 V
(d) 5 V

Explaination:

4. A coil of 100 turns carries a current of 5 mA and creates a magnetic flux of 10-5 weber. The inductance is
(a) 0.2 mH
(b) 2.0 mH
(c) 0.02 mH
(d) 0.002 H

Explaination:

5. Lenz’s law of electromagnetic induction is as per law of conservation of
(a) energy.
(b) momentum angular.
(c) charge.
(d) electromotive force.

Explaination:
(a) Work done in changing magnetic flux, is produced as induced e.m.f.

6. The current flows from A to B is as shown in the figure. The direction of the induced current in the loop is

(a) clockwise.
(b) anticlockwise.
(c) straight line.
(d) no induced e.m.f. produced.

Explaination:
(a) By lenz’s law, the induced current must produce inward flux to counter magnetic flux of AB. So induced current is clockwise in the loop.

7. In a coil of self-induction 5 H, the rate of change of current is 2 As-1. Then emf induced in the coil is
(a) 10 V
(b) -10 V
(c) 5 V
(d) -5 V

Explaination:
(b) Induced e.m.f. ε = -L$$\frac{dI}{dt}$$ = – 5 × 2 = -10 V

8. The north pole of a long bar magnet was pushed slowly into a short solenoid connected to a short 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 The magnet was held stationary for a few seconds with the north pole in the middle of the solenoid and then withdrawn rapidly.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

9. The magnetic flux linked with a coil of N turns of area of cross section A held with its plane parallel to the field B is

10. Faraday’s laws are consequence of the conservation of
(a) charge
(b) energy
(c) magnetic field
(d) both (b) and (c)

11. Two identical coaxial coils P and Q carrying equal amount of current in the same direction are brought nearer. The current in
(a) P increases while in Q decreases
(b) Q increases while in P decreases
(c) both P and Q increases
(d) both P and Q decreases

12. 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

13. Lenz’s law is a consequence of the law of conservation of
(a) charge
(b) energy
(c) induced emf
(d) induced current

14. A solenoid is connected to a battery so that a steady current flows through it. If an iron core is inserted into the solenoid, the current will
(a) increase
(b) decrease
(c) remain same
(d) first increase then decrease

15. Which of the following statements is not correct?
(a) Whenever the amount of magnetic flux linked with a circuit changes, an emf is induced in circuit.
(b) The induced emf lasts so long as the change in magnetic flux continues.
(c) The direction of induced emf is given by Lenz’s law.
(d) Lenz’s law is a consequence of the law of conservation of momentum.

16. There is a uniform magnetic field directed perpendicular and into the plane of the paper. An irregular shaped conducting loop is slowly changing into a circular loop in the plane of the paper. Then
(a) current is induced in the loop in the anti-clockwise direction.
(b) current is induced in the loop in the clockwise direction.
(c) ac is induced in the loop.
(d) no current is induced in the loop.

17. In the given figure current from A to B in the straight wire is decreasing. The direction of induced current in the loop is A

(a) clockwise
(b) anticlockwise
(c) changing
(d) nothing can be said

18. The north pole of a bar magnet is rapidly introduced into a solenoid at one end (say A). Which of the following statements correctly depicts the phenomenon taking place?
(a) No induced emf is developed.
(b) The end A of the solenoid behaves like a south pole.
(c) The end A of the solenoid behaves like north pole.
(d) The end A of the solenoid acquires positive potential.

19. A metal plate can be heated by
(a) passing either a direct or alternating current through the plate.
(b) placing in a time varying magnetic field.
(c) placing in a space varying magnetic field, but does not vary with time.
(d) both (a) and (b) are correct.

20. Identify the wrong statement.
(a) Eddy currents are produced in a steady magnetic field.
(b) Eddy currents can be minimized by using laminated core.
(c) Induction furnace uses eddy current to produce heat.
(d) Eddy current can be used to produce braking force in moving trains.

21. Which of the following does not use the application of eddy current?
(a) Electric power meters
(b) Induction furnace
(c) LED lights
(d) Magnetic brakes in trains

22. If number of turns in primary and secondary coils is increased to two times each, the mutual inductance
(a) becomes 4 times
(b) becomes 2 times
(c) becomes A times
(d) remains unchanged 4

23. When the rate of change oic current is unity, the induced emf is equal to
(a) thickness of coil
(b) number of turns in coil
(c) coefficient of self inductance
(d) total flux linked with coil

24. Two inductors of inductance .L each are connected in series with opposite? magnetic fluxes. The resultant inductance is
(Ignore mutual inductance)
(a) zero
(b) L
(c) 2L
(d) 3L

25. A square of side L metres lies in the x-y plane in a region, where the magnetic field is given by B = B0{li + 3j + 4k) T, where Bo is constant. The magnitude of flux passing through the square is [NCERT Exemplar]
(a) 2BoL² Wb.
(b) 3BoL² Wb.
(c) 4BoL² Wb.
(d) √29 BoL² Wb.

26. A loop, made of straight edges has six comers at A(0, 0, 0), B(L, 0, 0) C(L, L, 0), D(0, L, 0), E(0, L, L) and F(0,0, L). A magnetic field B = Bo ($$\hat{i}+\hat{k}$$)T is present in the region. The flux passing through the loop ABCDEFA (in that order) is [NCERT Exemplar]
(a) BoL² Wb.
(b) 2BoL² Wb.
(c) √2BoL² Wb.
(d) 4BoL² Wb.

27. A cylindrical bar magnet is rotated about its axis (Figure). A wire is connected from the axis and is made to touch the cylindrical surface through a contact. Then [NCERT Exemplar]

(a) a direct current flows in the ammeter A.
(b) no current flows through the ammeter A.
(c) an alternating sinusoidal current flows through the ammeter A with a time period T = $$\frac{2 \pi}{\omega}$$
(d) a time varying non-sinosoidal current flows through the ammeter.

28. There are two coils A 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 counterclockwise. B is kept stationary when A moves. We can infer that [NCERT Exemplar]

(a) there is a constant current in the clockwise direction in A.
(b) there is a varying current in A.
(c) there is no current in A.
(d) there is a constant current in the counterclockwise direction in A.

29. Same as question 4 except the coil A is made to rotate about a vertical axis (Figure). No current flows in B if A is at rest. The current in coil A, when the current in B (at t = 0) is counterclockwise and the coil A is as shown at this instant, t = 0, is [NCERT Exemplar]

(a) constant current clockwise.
(b) varying current clockwise.
(c) varying current counterclockwise.
(d) constant current counterclockwise.

30. An e.m.f is produced in a coil, which is not connected to an external voltage source. This is not due to
(a) the coil being in a time varying magnetic field.
(b) the coil moving in a time varying magnetic field.
(c) the coil moving in a constant magnetic field.
(d) the coil is stationary in external spatially varying magnetic field, which does not change with time.

31. Total number of magnetic lines of force crossing a surface normally is called _________ .

Explaination: magnetic flux

32. Relation between S.I. unit and C.G.S. unit of magnetic flux is _________ .

Explaination: 1 Weber = 108 Maxwell

33. Phenomenon of production of induced emf due to change of magnetic flux linked with a closed circuit is known as _________ .

Explaination: electromagnetic induction

34. Direction of induced current is such that it _________ the cause which produces it.

Explaination: opposes

35. A long straight current carrying wire passes normally through the centre of circular loop. If the current through the wire increases, will there be an induced emf in the loop? Justify.
[Delhi 2017]

Explaination: No current will be induced since the field lines are lying in the plane of the closed loop.

36. The electric current flowing in a wire in the direction from B to A is decreasing. Find out the direction of the induced current in the metallic loop kept above the wire as shown. [AI 2014]

Explaination: Clockwise.

37. What is the direction of induced currents in metal rings 1 and 2 when current I in the wire is increasing steadily? [AI2017]

Explaination:
The direction of induced current is clockwise in metal ring 1 and anticlockwise in metal ring 2.

38. Use Lenz’s law to determine the direction of the induced current when a rectangular conducting loop abed is moved into a region of magnetic field which is directed normal to the plane of the loop away from the reader. [Foreign 2014]

Explaination:
On moving a rectangular conducting loop into the field, the flux increases. According to Lenz’s law, the induced current would be anticlockwise.

39. A triangular loop of wire placed at abc is moved completely inside a magnetic field ’which is directed normal to the plane of the loop away from the reader to a new position a’b’c’. What is the direction of the current induced in the loop? Give reason. [Foreign 2014]

Explaination:
A triangular loop remains inside the magnetic field throughout its motion. The free charges do not find path to complete the circuit. So, no current is induced.

40. Two bar magnets are quickly moved towards a metallic loop connected across a capacitor C as shown in the figure. Predict the polarity of the capacitor. [AI 2017, 2011]

Explaination: The upper plate is having +ve polarity and the lower plate is having -ve polarity.

41. 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 show in the figure.

Explaination: Anticlockwise: As seen from the side opposite to the magnet.

42. A closed loop is held stationary in the magnetic field between the north and south poles of two permanent magnets held fixed. Can we hope to generate current in the loop by using very strong magnets?

Explaination:
No. However strong the magnet may be, current can be induced only by changing the magnetic flux through the loop.

43. A closed loop moves normal to the constant electric field between the plates of a large capacitor. Is a current induced in the loop
(i) when it is wholly inside the region between the capacitor plates, and
(ii) when it is partially outside the plates of the capacitor? The electric field is normal to the plane of the loop.

Explaination:
No current is induced in either case. Current cannot be induced by changing the electric flux.

44. A bar magnet is moved in the direction indicated by the arrow between two coils PQ and CD. Predict the directions of induced current in each coil.

Explaination:
The direction of induced current clockwise in coil PQ as seen from magnet side.
The direction of induced current clockwise in coil CD as seen from magnet side.

45. Twelve wires of equal length are connected to form a skeleton cube which moves with a velocity v parallel to the magnetic field $$\vec{B}$$. What will be the induced emf in each arm of the cube? [HOTS]

Explaination:
$$F=q(\vec{v} \times \vec{B}) \cdot \operatorname{As} \vec{v} \| \vec{B}$$ force on electrons in any arm of the cube is zero. Hence, no emf is induced.

46. Two spherical bobs, one metallic and the other of glass, of the same size are allowed to fall freely from the same height above the ground. Which of the two would reach earlier and why? [Delhi 2014]

Explaination:
A glass bob, as in the glass bob, there is no effect of electromagnetic induction due to the presence of earth’s magnetic field, unlike in the case of a metallic bob.

47. A circular loop is moved through the region of uniform magnetic field. Find the direction of induced current (clock wise or antic lock wise) when the loop moves (i) into the e field, and (ii) out of the field. [Foreign 2010]

Explaination: (i) Anticlockwise, (ii) Clockwise

48. A rectangular loop of wire is p right, away from the long straight wire through which a steady current I flows upwards. What is the direction of induced current in the loop?

Explaination: Clockwise.

49. When a coil is rotated in a uniform magnetic field at constant angular velocity, will the magnitude of induced emf set up in the coil be constant? Why? [HOTS]

Explaination:
No, the induced emf will vary with time and will be sinosoidal due to the change in orientation of the coil w.r.t. the magnetic field.

50. A light metal disc on the top of an electromagnet is thrown up as the current is switched on. Why? Give reason. [AI2013]

Explaination:
Due to the eddy currents. As these currents produce opposite polarity on the lower side of the disc.

51. A current carrying wire (straight) passes inside a triangular coil as shown in figure. The current in the wire is perpendicular to paper inwards. Find the direction of induced current in the loop if current in the wire is increasing with time. [DoE]

Explaination:
The magnetic field lines are tangential to the triangular plane, i.e.
θ = 90.

Hence. Φ = 0.
∴ Induced emf = 0
∴ Induced current = 0

52. How does the mutual inductance of a pair of coils change when
(i) distance between the coils is increased and
(ii) number of turns in the coils is increased? [AI 2013]

Explaination:
(i) When the distance between a pair of coils is increased, the magnetic flux linked with the secondary coil decreases and hence, the mutual inductance between them will decrease.
(ii) Since M ∝ N1 N2, so, when number of turns in the coil is increased, the mutual inductance will also increase.

53. The closed loop (PQRS) of wire is moved into a uniform magnetic field at right angles to the plane of the paper as shown in the figure. Predict the direction of the induced current in the loop. [Foreign 2012]

Explaination: Anticlockwise.

54. The current i in an induction coil varies with time t according to the adjoining graph.

Draw the graph of induced emf with time. [DoE]

Explaination: Induced emf, E = -L$$\frac{dI}{dt}$$

55. A rod PQ of length 1 is moved in uniform magnetic field $$\vec{B}$$ as shown. What will be the emf induced in it?

Explaination: e = Blv sin θ

56. Predict the direction of induced current in a metal ring when the ring is moved towards a straight conductor
with constant speed v. The conductor is carrying current I in the direction shown in the figure. [Delhi 2012]