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

### CBSE Class 12 Physics MCQs Solution All Chapters

Free PDF 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 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 MCQ Chapter 6

Below are some of the very important NCERT Electromagnetic Induction MCQ Class 12 Physics Chapter 6 with answers. These Electromagnetic Induction MCQ have been prepared by expert teachers and subject experts based on the latest syllabus and pattern of CBSE Term 1 examination.

We have given these Electromagnetic Induction MCQ Class 12 Physics questions with answers to help students understand the concept.

MCQ Questions for Class 12 Physics are very important for the latest CBSE Term 1 and Term 2 pattern. These MCQs are very important for students who want to score high in CBSE Board, NEET and JEE exam.

### MCQ 1- 44

1 . A moving conductor coil is a magnetic field produces an induced EMF this is in accordance with

1. Lenz’s law
2. Coulomb’s law
4. Ampere’s law

3

2. An induced EMF is produced when a magnet is plunged into a coil. The strength of the induced EMF is independent of

1. number of turns of coil
2. speed with which the magnet is moved
3. the strength of magnet
4. the resistivity of the wire of the coil

4

3. The magnetic flux through a coil is inversely proportional to

1. magnetic field
2. number of turns
3. area
4. none of these

4

4. Faraday’s law are consequences of conservation of

1. energy & magnetic field
2. energy
3. magnetic field
4. charge

2

5. Lenz’s law give

1. the direction of the induced current
2. the magnitude of the induced EMF
3. the magnitude of the induced current
4. Both the magnitude and direction of the induced current

1

6. Which of the following phenomena makes use of electromagnetic induction?

1. magnetising an iron piece with a bar magnet
2. generation of hydroelectricity
3. magnetizing a soft iron piece by placing inside a current carrying solenoid
4. charging a storage battery

2

7. The magnetic flux (ф) linked with a coil due to its own magnetic field is related to the number of turns of coil as

1. Ф ∝ N2
2. Ф ∝ N-1
3. Ф ∝ N
4. Ф ∝ N-2

1

8. In electromagnetic induction, the induced charge is independent of

1. resistance of the coil
2. change of flux
3. time
4. none of these

3

9. To induce an EMF in a coil, the linking magnetic flux

1. must remain constant
2. can either increase or decrease
3. must increase
4. must decrease

2

10. The magnetic flux through a circuit of resistance R changes by an amount ΔΦ in a time Δt. Then the total quantity of the electric charge Q that passes through any point in the circuit during the time Δt is represented by

1. Q = ΔΦ / R
2. Q = RΔΦ / Δt
3. Q = ΔΦ / RΔt
4. Q = ΔΦ / Δt

1

11. A coil has 200 turns and area of 70 cm2 . The magnetic field perpendicular to the plane of the coil is 0.3 Wb/m2 and takes 0.1 s to rotate through 180°. The value of the induced EMF will be

1. 84 V
2. 42 V
3. 8.4 V
4. 4.2 V

3

12. The expression for the induced EMF contains and negative sign. What is the significance of the negative sign?

1. The induced EMF is opposite to the direction of the flux
2. The induced EMF is produced only when the magnetic flux decreases
3. The induced EMF opposes the changes in the magnetic flux
4. None of the above

3

13. Lenz’s and Faraday’s law is expressed by the following formula

1. e = -NdΦ/dt
2. e = NdΦ/dt
3. e = -ΦdN/dt
4. e = -d(Φ/N)/dt

1

14. A rectangular coil of 100 turns and size 0.1 X 0.05 m is placed perpendicular to a magnetic field of 0.1 T. If the field drops to zero point 0.05T in 0.05 s, the magnitude of the EMF induced in the coil is

1. 0.5
2. 3
3. 2
4. 6

1

15. An electron moves along the line AB, which lies in the same plane as a circular loop of conducting wire as shown in the diagram. What will be the direction of current induced, if any, in the loop?

1. The current will change direction as the electron passes by
2. The current will be anticlockwise
3. The current will be clockwise
4. No current will be induced

1

16. Eddy Currents may be reduced by using

1. thick piece of Cobalt
2. thick piece of Nickel
3. laminated core of Steel
4. laminated core of soft iron

4

17. When current changes from 13A to 7A in 0.5s through a coil the EMF induced is 3 x 10-4. The coefficient of self induction is

1. 25 x 10-6 H
2. 25 x 10-5 H
3. 25 x 10-4 H
4. 25 x 10-3 H

1

18. Magnetic flux of 10μWb is linked with a coil, when a current of 2mA flows through it. What is the self inductance of the coil?

1. 20mH
2. 10mH
3. 15mH
4. 5 mH

4

19. For two coils with number of turns 500 and 200 each of length 1 m and cross sectional area 4 x 10-4 m2, the mutual inductance is

1. 0.5 μH
2. 0.5 H
3. 5 μH
4. 0.05 mH

4

20. When current I passes through an inductor of inductance L, energy stored in it is 1/2LI2. This is stored in the

1. electric field
2. magnetic field
3. voltage
4. current

2

21. A small coil of N1 turns, l1 length is tightly wound over the centre of long solenoid of length l2, area of cross section A and number of turns N2. If a current I flows in the small coil, then the flux through the long solenoid is

1. Zero
2. μoN1N2AI/l1
3. μoN12AI/l1
4. Infinite

2

22. Which of the following is not a factor to determine the mutual inductance of the two coils

1. current through each coil
2. the number of terms of each coil
3. separation between the coils
4. the shape of each coil

1

23. Mutual inductance of two coils can be increased by

1. winding the coils on wooden coil
2. decreasing the number of turns in the coil
3. increasing the number of turns in the coil
4. none of these

3

24. The mutual inductance between two coils depend upon

1. medium between the coils
2. separation between coils
3. neither 1 nor 2
4. both 1 and 2

4

25. Self inductance ___________ when the number of turns of a coil is doubled

1. is halved
2. is doubled
3. becomes 4 times
4. becomes one quarter

3

26. Self induction of a solenoid is

1. inversely proportional to area of cross section
2. directly proportional to area of cross section
3. directly proportional to its length
4. directly proportional to current flowing through the coil

2

27. Two solenoids of same cross sectional area have the length and number of turns in ratio 1:2 both. The ratio of self inductance of two solenoids is

1. 1:2
2. 2:1
3. 1:4
4. 1:1

1

28. For perfect coupling of two coils of inductance L1 and L2 their mutual inductance M should be given by

1. M = √ (L1L2)
2. M = L1 / L2
3. M = (L1L2)½
4. M = L1L2

1

29. In an inductor of inductance L=100mH, a current of I=10A is flowing. The energy stored in the inductor is

1. 1000 J
2. 100 J
3. 10 J
4. 5 J

4

30. What will be the self inductance of a coil of 100 turns if a current of 5A produces a magnetic flux of 5 x 10-5 Wb?

1. 1 μH
2. 10μH
3. 1mH
4. 10mH

3

31. If the current 30A flowing in the primary coil is made zero in 0.1 s, the EMF induced in the secondary coil is 1.5V. The mutual inductance between the coil is

1. 0.1 H
2. 0.2 H
3. 0.005 H
4. 1.05 H

3

32. The physical quantity which is measured in the unit of WbA-1 is

1. magnetic flux
2. self inductance
3. mutual inductance
4. both B and C

4

33. The coefficient of mutual inductance of two coils is 6mH. If the current flowing in one is 2A, then the induced EMF in the second coil will be

1. Zero
2. 2mV
3. 3mV
4. 3V

1

34. An EMF of 12V is induced in a given coil when the current in it changes at a rate of 48A/min. The inductance of the coil is

1. 9.6 H
2. 15 H
3. 0.25 H
4. 1.5 H

2

35. The mutual inductance of a pair of coil is 0.75 H. If current in the primary coil changes from 0.50A to zero in 0.01s, find average induced EMF is in secondary coil

1. 22.5 V
2. 12.5 V
3. 25.5 V
4. 37.5 V

4

36. In an inductor, having a self inductance of 10 H, the current changes from 10A to 5A in 0.2s. The induced EMF in inductor is

1. 2.5 V
2. 10 V
3. 25 V
4. 250 V

4

37. Energy stored in a coil of self inductance 40mH carrying a steady current of 2A is

1. 8J
2. 0.08J
3. 0.8J
4. 80J

2

38. The mutual inductance of an induction coil is 5H. In the primary coil, the current reduces from 5A to zero in 10-3s. What is the induced EMF in the secondary coil?

1. Zero
2. 2500 V
3. 2510 V
4. 2500 V

4

39. An air core solenoid has 1000 turns and is 1 m long. Its cross-sectional area is 10 cm2. Its self inductance is

1. 0.1256 mH
2. 1.256 mH
3. 12.56 mH
4. 125.6 mH

2

40. A square of side L in lies in the x-y plane in a region, where the magnetic field is given by, B = Bo (2i + 3j + 4k) T, where Bo is a constant. The magnitude of flux passing through the square is

1. 2BoL2Wb
2. 3BoL2Wb
3. 4BoL2Wb
4. √29BoL2L2Wb

3

41. A loop, made of straight edges has six corners 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(i+k) T is present in the region. The flux passes through the loop in the region. The flux passing through the loop ABCDEFA is

1. BoL2Wb
2. 2BoL2Wb
3. √2BoL2Wb
4. 4BoL2Wb

2

42. There are two coils A and B as shown in the 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 conclude that

1. there is a constant current in the clockwise direction in A
2. there is a very current in A
3. there is no current in a there is A
4. constant current in the counterclockwise direction in A

4

43. The self inductance L of a solenoid of length l and area of cross section A, with a fixed number of turns N increases as

1. l and A increases
2. l decreases and A increases
3. l increases and A decreases
4. both l and A decrease

1

44. A circular loop of radius r, carrying a current I lies in the y-z plane with its centre at the origin. The net magnetic flux through the loop is

1. directly proportional to r
2. zero
3. inversely proportional to r
4. directly proportional to I

2

### Assertion-Reasoning Based MCQ

Code

1. Both assertion and reason are true and reason is the correct explanation of assertion.
2. Both assertion and reason are true but reason is not the correct explanation of assertion.
3. Assertion is true but reason is false.
4. Assertion is false but reason is true.

A

1 . Assertion Faraday’s law are consequence of conservation of energy

Reason In a pure resistive AC circuit, the current lags behind the EMF in phase

1. (3)

According to Faraday’s laws, the conversion of mechanical energy into electrical energy. This is in accordance with the law of conservation of energy. In pure resistance, the EMF is in with phase the current.

2. Assertion Lenz’s law is based on the principle of conservation of energy

Reason Induced EMF always opposes the change in magnetic flux responsible for its production

2. (1)

Lenz’s law is based on conservation of energy and induced EMF opposes the cause of it, i.e, change in magnetic field.

3. Assertion Two identical loops one of copper and other of aluminium and rotated with the same speed in the same magnetic field. The EMF induced in both the loop will be same.

Reason The magnitude of induced EMF is directly proportional to the rate of change of magnetic flux linked with the circuit

3. (1)

Since both the loops are identical and moving with the same speed in same magnetic field, same emf is induced in both the coils. But the induced current will be more in the copper loop as its resistance will be lesser as compared to that of aluminium loop.

4. Assertion An induced current will be developed in a conductor, if it is moved in a direction parallel to the magnetic field.

Reason Whenever there is relative motion between loop and magnet and induced current is produced in the loop.

4. (4)

Induced current will not be developed in a conductor if a conductor, if it is move in the direction parallel to magnetic field. It is because, in this case, the Lorentz force on free electrons in the conductor is zero. The induced EMF is produced only when the magnetic flux linked with the loop changes.

5. Assertion Eddy Currents are produced in a metallic conductor when magnetic flux is changed around it

Reason Electric potential determines the flow of charge

5. (2)

When a metallic conductor is moved in a magnetic field, magnetic flux is varied. It disturbs the free electrons of the metal and set up an induced EMF in it. As there are no free ends of the metal, it will be closed in itself so there will be induced current.

6. Assertion An artificial satellite with a metal surface is moving above the earth in a circular orbit. A current will be induced in the satellite if the plane of the orbit is inclined to the plane of the equator.

Reason The current will be induced only when the speed of satellite is more than 8 km/sec

6. (3)

When the satellite moves in inclined plane with equitorial plane, the value of magnetic field will change both in magnitude and direction. Due to this, the magnetic flux through the satellite will change and hence induced currents will be produced in metal of the satellite. But no current will get induced if satellite orbits in the equitorial plane because the magnetic flux does not change through the metal of the satellite in this plane.

7. Assertion An induced EMF is generated when magnet is withdrawn from the solenoid

Reason The relative motion between magnet and solenoid induces EMF

7. (1)

EMF is induced when there is change in magnetic flux.

8. Assertion Only a change in magnetic flux will maintain and induced current in the coil

Reason The presence of large magnetic flux through a coil maintains the current in the coil electric circuit is continuous

8. (3)

Presence of magnetic flux can not produce current.

9. Assertion mutual inductance of a pair of coil depends on the separation as well as the relative orientation

Reason mutual inductance depends upon the length of the coil only

9. (3)

The mutual inductance in case of a medium of relative permeability is

M = (μoμrπN1N2r22) / l

10. Assertion in the phenomenon of mutual inductance self induction of each of the coil possessed

Reason self induction rises due to change in current in the coil itself in mutual induction current changes in both the individual coil

10. (3)

Mutual inductance is the phenomenon according to which an opposing EMF produces flux in a coil as a result of change in current on magnetic flux linked with a neighbouring coil. But when two coils are inductively coupled in addition to induced EMF produced in each of two coils due to self induction.

11. Assertion the self inductance of a long solenoid is proportional to the area of cross section and length of the solenoid

Reason self inductance of a solenoid is independent of the number of turns per unit length

11. (3)

The self inductance of a solenoid is given by L = μoμrn2Al

12. Assertion when two coils are wound on each other the mutual inductance between the coil is maximum

Reason mutual inductance does not depend on the orientation of the coils

12. (3)

The manner in which the two coils are oriented, determines the coefficient of coupling between them

M = K√L1L2

When two coils are wound on each other, the coefficient of coupling is maximum and hence mutual inductance between the coil is maximum.

13. Assertion inductance coil are made of copper

Reason induced current is more in wire having less resistance

13. (1)

The inductance coils made of copper will have very small ohmic resistance. Due to change in magnetic flux a large induced current will be produced in such an inductance, which will offer appreciable opposition to the flow of current.

### Case-Study Based MCQ

1 . Lenz’s law is the mostly used to find the direction current induced in a circuit. According to this law, the polarity of EMF induced in the circuit is such that it opposes or check the variation in magnetic flux responsible for it.

If we move north pole of a bar magnet towards coil, then magnetic flux linked with the coil changes (i.e. increases). Due to this current is induced in the coil in anticlockwise direction. The magnetic moment related with induced current has not polarity towards the north pole. If we move away the bar magnet the magnetic moment has south polarity.

Lenz’s law was the law of conservation of energy.

(i) Lenz’s law is used to find the direction of

(a) electric field

(b) force

(c) induced current

(d) electrostatic force

(ii) Lenz’s law follows the law of

(a) conservation of force

(b) conservation of mass

(c) conservation of momentum

(d) conservation of energy

(iii) What will be the polarity of magnetic moment if we move the north of magnet towards coil?

(a) North

(b) South

(c) Both (a) and (b)

(d) None of these

(iv) If we move away the bar magnet from coil then what will be the direction of induced current in coil.

(a) clockwise

(b) anticlockwise

(c) both (a) and (b)

(d) none of these

(v) As the move the north pole of magnet towards coil, the magnetic flux linked with the coil

(a) increases

(b) decreases

(c) remains same

(d) none of these

2. From the experimental observations for after arrived at a conclusion that an EMF is induced in a coil when magnetic flux through the coil changes with time. The change in magnetic flux induces EMF in coils C1. It was this induced EMF which cost electric current to flow in coil C1 and through the galvanometer.

When the tapping key K is pressed, the current enquiry C2 (and the result in magnetic field) rises from zero to a maximum value in a short time. Consequently, the magnetic flux through the neighboring coil C1 also increases. It is the change in magnetic flux through a point C1 that produces an induced EMF in a coil C1.

The SI unit of magnetic flux is weber. When the key is held pressed current in coil C2 is constant. Therefore, there is no change in the magnetic flux through coil C1 and the current in coil C1 drops to zero. When the key is released, the current in C2 and the resulting magnetic field decreases from the maximum value to zero in a short time.

This results in a decrease in magnetic flux through coil C1 and hence again induces an electric current in coil C1. The common point in all his observation is that the time rate of change in magnetic flux through a circuit induces EMF in it.

Faraday stated experimental observation in form of law called Faraday’s law of electromagnetic induction which states that ‘the magnitude of induced EMF in a circuit is equal to time rate of change of magnetic flux through the circuit.

(i) What is the full form of EMS?

(a) electron movement force

(b) electromotive force

(c) electron monitoring force

(d) electromagnetic field

(ii) Which of the following scientist arrived at a conclusion that an EMF is induced in a coil when magnetic flux through the coil changes with time

(b) Joseph Henry

(d) Blaise Pascal

(iii) What is the SI unit of magnetic flux?

(a) Pascal

(b) Coulomb

(c) Weber

(d) Tesla

(iv)Who among the following scientist gave the statement, ‘the magnitude of the induced EMF in a circuit is equal to the time rate of change of magnetic flux through the circuit’?

(a) John Dalton

(b) Joseph Henry

(c) Blaise Pascal

(v) A rod of length 0.4 m moves in a direction perpendicular to a magnetic field of magnitude 1.2 T. The EMF induced in the moving rod is found to be 2.4 V. What is the speed of the rod?

(a) 0.48 m/s

(b) 2.88 m/s

(c) 7.2 m/s

(d) 5.0 m/s

3. So far we have studied about the electric currents induced in well defined paths in conductor like circular loops. Even when bulk pieces of conductors are subjected to changing magnetic flux, induced currents are produced in the. However, their flow patterns resemble swirling eddies in water.

This effect was discovered by physicist Foucault (1819-1868) and these currents are called eddy currents. A copper plate is allowed to swing like a simple pendulum between the pole pieces of a strong magnet. It is found that the motion is damped and in a little while, the plate comes to a halt in the magnetic field.

We can explain this phenomenon on the basis of electromagnetic induction. Magnetic flux associated with the plate keeps on changing as the plate moves in and out of the region between magnetic poles. The flux change induces eddy currents in the plate. Directions of eddy currents are opposite when the plate swings into the region between the poles and when it swings out of the region.

(i) In which year Faucault was born?

(a) 1819

(b) 1825

(c) 1838

(d) 1868

(ii) Even when bulk pieces of conductors are subjected to changing magnetic flux, induced currents are produced in them. This effect was discovered by which of the following scientist?

(a) John Dalton

(b) Jean Bernard Leon Faucault

(c) Heinrich Friedlich Lenz

(iii) What is called magnetic flux?

(a) Magnetic flux is a vector field that describes the magnetic influence on moving electric charges, electric currents and magnetic materials.

(b) Magnetic flux is the production of an electromotive force across an electric conductor in a changing magnetic fields.

(c) Magnetic flux is a measurement of the total magnetic field which passes through a given area.

(d) Magnetic flux is a rectangular piece of an object that shows permanent magnetic properties and are made from the ferromagnetic substance.

(iv) Eddy current can be defined as

(a) Eddy currents are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday’s law of induction.

(b) Eddy currents are the magnitude of the induced EMF in a circuit is equal to the time rate of change of magnetic flux through that circuit

(c) Eddy currents are the polarity of induced EMF such that it tends to produce a current which opposes the change in magnetic flux that produces it.

(d) None of these

(v) If a current of 2A gives rise to a magnetic flux of 5 x 10-5 Wb through a coil having 100 turns, then the magnetic energy stored in the medium surrounding the coil is

(a) 5 J

(b) 50 J

(c) 5 x 10-3 J

(4) 0.5 J

### Electromagnetic Induction Class 12 Physics MCQs

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]  