# MCQ of Electromagnetic Induction | Chapter 6 | Physics | Class 12 |

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MCQ of Electromagnetic Induction, Chapter 6, Class 12, Physics

Question 1: In Faraday’s experiment on electromagnetic induction, more deflection will be shown by the galvanometer, when

1. Magnet is in constant motion towards the coil
2. Magnet is in constant motion away from the coil
3. Magnet is in accelerated motion towards the coil
4. Magnet is at rest near the coil

Answer: C ( Magnet is in accelerated motion towards the coil )

Question 2: The inductance of a coil is proportional to

1. The length
2. The number of turns
3. The resistance of coil
4. The square of the number of turns

Answer: D (The square of the number of turns)

Question 3: A bar magnet is dropped between a current carrying coil. What would be its acceleration?

1. g downwards
2. Greater than g downwards
3. Less than g downwards
4. Bar will be stationary

Answer: C (Less than g downwards)

Question 4: In a solenoid, if number of turns is doubled, then self inductance will become

1. Half
2. Double
3. 1 / 4 times

Question 5: According to Lenz’s law of electromagnetic induction

1. The relative motion between the coil and the magnet produces change in magnetic flux
2. The direction of induced emf is such that it supports the change in magnetic flux
3. Only the coil should be moved towards the magnet for production of induced emf
4. Only the magnet should be moved towards coil for the generation of  induced electric field

Answer: A ( The relative motion between the coil and the magnet)

Question 6: A horizontal conducting rod 10 m long extending from east to west is falling with speed 5 ms-1 at right angles to horizontal component of the earth’s magnetic field 0.3 x 10-4 wbm-2. Find the instantaneous value of emf induced in the coil.

1. 15 x 10-3 V
2. 1.5 x 10-3 V
3.  0.3 x 10-4
4. None of these

Answer: B ( 1.5 x 10-3 V )

You may also go through other subjects like MCQs of Biology, Physics, Chemistry, Music, Accountancy, Business Studies, Economics, Geography, Political Science & English for having a strong hold on the subject with an intent to score higher in the first term examination to be held in the month of November/December.

Question 7: A magnet is moved towards a coil i) speedly  ii) slowly then induced emf/ induced charge will be respectively

1. More in first case / more in first case
2. More in first case / equal in both cases
3. Less in first case / more in second case
4. Less in first case / equal in both cases

Answer: B ( More in first case / equal in both cases )

Question 8: The magnetic flux linked with the coil, in Webers, is given by the equation Φ = 3 t2 + 4 t + 9 . Then the magnitude of induced emf at time t=2 s will be

1. 2 V
2. 4 V
3. 8 V
4. 16 V

Question 9: Lenz’s law is in accordance with law of conservation of

1. Charge
2. Momentum
3. Energy
4. Current

Question 10: What is increased in step down transformer?

1. Voltage
2. Current
3. Power
4. Current density

Question 11: In a transformer, number of turns in the primary coil are 140 and that in the secondary coil are 280. If current in primary is 4 A then that in secondary is

1. 4 A
2. 2 A
3. 6 A
4.  10 A

You may also read MCQ of Electric Charges and Fields, MCQ of Electrostatic Potential and Capacitance, MCQ of Current Electricity, MCQ of Moving Charges and Magnetism, MCQ of Magnetism and Matter, MCQ of Alternating Current for better understanding of the chapters.

Question 12: An inductor L , a resistance R and two identical bulbs B1 and B2 are connected to a battery through a switch as as shown below. Which of the following statements gives the correct description of the happenings when the switch S is closed?

1. The bulb B2 lights up earlier than B1 and finally both the bulb shine equally bright
2. B1 lights up earlier and finally both the bulbs acquire equal brightness
3. B2 lights up earlier and finally B1 shines brighter than B2
4. B1 and B2 light up together with equal brightness all the time

Answer : C (B2 lights up earlier and finally B1 shines brighter than B2)

Question 13: Which one of the following is a correct statement?

1. Electric field is always conservative
2. Electric field due to a varying magnetic field is conservative
3. Electric field is conservative due to electrostatic charges while non-conservative due to a time varying magnetic field
4. Electric field lines are always closed loops

Answer : C (Electric field is conservative due to electrostatic charges while non-conservative due to a time varying magnetic field)

Question 14 : Eddy currents are produced when

1. A metal is kept in varying magnetic field
2. A metal is kept in a steady magnetic field
3. A circular coil is placed in a magnetic field
4. Through a circular col current is passed

Answer : A (A metal is kept in varying magnetic field)

Question 15: The core used in a transformer and other  electromagnetic devices is laminated so that

1. Ratio of voltage in the primary and secondary may be increased
2. Energy loss due to Eddy currents may be minimised
3. The weight of the transformer may be reduced
4. Residual magnetism in the core may be reduced

Answer : B (Energy loss due to Eddy currents may be minimised)

Question 16: Two coils X and Y are placed in a circuit such that when the current changes by 2 A in the coil X the magnetic flux changes by 0.4 Wb in Y. The value of mutual inductance of the coils is

1. 0.2 H
2. 5 H
3. 0.8 H
4. 4 H

Question 17: A metal ring is attached with the wall of a room. When the north pole of as magnet is brought near it, the induced current in the current will be

1. First clockwise then anticlockwise
2. In clockwise direction
3. In anticlockwise direction
4. First clockwise and then anticlockwise

Answer : C (In anticlockwise direction)

Question 18: In the given figure, current from A to B is decreasing. The direction of induced current in the loop is

1. Clockwise
2. Anticlockwise
3. Changing
4. Nothing can be said

Question 19: Induction furnace is based on the principle of

1. Self induction
2. Mutual induction
3. Eddy current
4. None of these

Question 20: When the plane of the armature of an a.c. generator is parallel to the field, in which it is rotating

1. Both the flux linked and emf induced in the coil are zero
2. The flux linked with it is zero, while induced emf is maximum
3. Flux linked is maximum while induced emf is zero
4. Both the flux linked and emf have their respective maximum values

Answer : B ( The flux linked with it is zero, while induced emf is maximum )

Question 21: Two circular coils can be arranged in any of the three ways as shown below. Their mutual inductance will be

1. Maximum in situation (i)
2. Maximum in situation (ii)
3. Maximum in situation (iii)
4. Same in all situations

Answer : A ( Maximum in situation (i) )

Question 22: A coil having 500 square loops each of side 10 cm is placed normal to a magnetic flux which increases at the rate of 1.0 T/s. The induced emf in volts is

1. 0.1
2. 0.5
3. 1
4. 5

Question 23: Two different loops are concentric and lie in the same plane. The current in the outer loop is clockwise and increasing with time. The induced current in the inner loop the, is

1. Clockwise
2. Zero
3. Counter clockwise
4. In a direction that depends on the ratio of loop radii

Question 24: Two coils of self inductance 2 mH and 8 mH are placed so close together that the effective flux in one coil is completely linked with the other. The mutual inductance between these coils are

1. 16 mH
2. 10 mH
3. 6 mH
4. 4 mH

Question 25: The energy stored in coil carrying current I is U. If current is halved, then energy stored in the coil will be

1. U / 2
2. U / 4
3. 2 U
4. 4 U

Answer : B (U / 4)

Question 26: The number of turns in the coil of an ac generator is 5000 and the area of the coil is 0.25 m. The coil is rotated at the rate of 100 cycles/ sec in a magnetic field of 0.2 Wb/m2. The peak value of the emf generated is nearly

1. 786 kV
2. 440 kV
3. 220 kV
4. 157.1 kV

Question 27: The frequency of an ac generator is altered with change in

1. Speed or rotation of coil
2. Amplitude of a.c.
3. Size of coil
4. All of the above

Answer : A (Speed or rotation of coil)

Question 28: The coefficient of mutual induction between two circuits is equal to the, emf produced in one circuit when current in second circuit is

1. Kept steady at 1 A
2. Cut – off at 1 A level
3. Changed at the rate of 1 A / s
4. Changed from 1 A/s to 2 A/s

Answer : C (Changed at the rate of 1 A/s)

Question 29: Consider the following statements
A) An EMF can be induced by moving a conductor in a magnetic field
B) An EMF can be induced by changing the magnetic field

1. Both A and B are true
2. A is true but B is false
3. B is true but A is false
4. Both A and B are false

Answer : A ( Both A and B are true)

Question 30: A metallic rod of 1 m length is rotated with a frequency of 50 revolution per second, with one end hinged at the centre and the other end at the circumference of a circular metallic ring of radius 1 m about an axis passing through the centre and perpendicular to the plane of the ring. A constant uniform magnetic field of 1 T parallel to the axis is present everywhere. The emf between the centre and the metallic ring is

1. 157 V
2. 117 V
3. 127 V
4. 137V

Question 31: Two different coils have self-inductances L1=8 mH and L2 =2 mH. The current in one coil is increased at a constant rate. The current in second coil is also increased at the same constant rate. At certain instant of time, the power given to the coils is the same. At that time, the current, the induced voltage and the energy stored in the first coil are i1, V1, and W1 respectively. Corresponding values for the second coil at the same instant are i2 , V2 and W2 respectively. Then choose the wrong option.

1.  i1 / i2 = 1 / 4
2. i1 / i2 = 4
3. W1 / W2 = 1 / 4
4. V1 / V2 = 1/ 4

Answer : B ( i1 / i2 = 4 )

Question 32: The working of generator is based upon

1. Magnetic effect of current
2. Heating effect of current
3. Chemical effect of current
4. Electromagnetic induction

Question 33: 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 decreases

Answer : B ( l decreases and A increases )

Question 34: Which of the following does not use the application of eddy current?

1. Electric power meters
2. Induction furnace
3. LED lights
4. Magnetic brakes in trains

Question 35: The coefficient of mutual induction depends on

1. Medium between the coils
2. Distance between the coils
3. Orientation of the two coils
4. All of these

Answer : D (All of these)

Question 36: A copper rod of length l rotates about its end with angular velocity ω in a uniform magnetic field B. The emf developed between the ends of the rod if the field is normal to the plane of rotation is

1. Bωl2
2. 1/2  Bωl2
3. 2 Bωl2
4. 1/4 Bωl2

Answer : B ( 1/2  Bωl2 )

Question 37: A coil and a bulb are connected in series with a dc source, a soft iron core is inserted in the coil, then

1. Intensity of the bulb remains the same
2. Intensity of the bulb decreases
3. Intensity of the bulb increases
4. The bulb ceases to glow

Answer : B (Intensity of the bulb decreases)

Question 38: Two particles each of mass m and charge q are attached to the ends of a light rigid rod of length 2R. The rod is rotated at constant angular speed about a perpendicular axis passing through its centre. The ratio of magnetic moment of the system and its angular moment about the centre of rod is

1. q / 2m
2. q / m
3. 2q / m
4. q / πm

Answer : A (q / 2m)

Question 39: The transformation ratio in the step up transformer is

1. 1
2. Greater than one
3. Less than one
4. The ratio greater or less than one depends on the other factors

Answer : B [ (Greater than one)]

Question 40: The mutual inductance between a primary and secondary circuits is 0.5 H. The resistance of the primary and secondary circuits are 20 ohm and 5 ohm respectively. To generate a current of 0.4 A in secondary, current in primary must be changed at rate of

1. 4.0 A/s
2. 1.6 A/s
3. 16.0 A/s
4. 8.0 A/s

Question 41: A wheel with ten metallic spokes each 0.50 m long is rotated with a speed of 120 rev/min in a plane normal to the earth’s magnetic field at the plane. If the magnitude of the field is 0.4 G, the induced emf between the axle and the rim of the wheel is equal to

1. 1.256 x 10-3 V
2. 6.28 x 10 -4 V
3. 1.256 x 10 -4 V
4. 6.28 x 10-5 V

Answer : D ( 6.28 x 10-5 V )

Question 42: An a.c. generator consists of coil of 200 turns and cross sectional area of 3 m2, rotating at a constant angular speed of 60 radian / sec in a uniform magnetic field of 0.04 T. the resistance of the coil is 500 ohm. What is the maximum power dissipated in the coil?

1. 518.4 W
2. 1036 W
3. 259.2 W
4. Zero

Question 43: A long solenoid has a inductance L and resistance R. It is broken into two equal parts and then joined in parallel. The combination is joined to cell of emf E. The time constant for the circuit will be

1. L / 4 R
2. 2 L / R
3. L / R
4. L / 2 R

Answer : C ( L / R)

Question 44: A circular coil expands radially in a region of magnetic field and no electromotive force is produced in the coil. This is because

1. The magnetic field is constant
2. The magnetic field is in the same plane as the circular coil and it may or may not vary
3. The magnetic field has a perpendicular (to the plane of the coil) component whose magnitude is decreasing suitably
4. Both B and C are correct

Answer : D (Both B and C are correct)

Question 45: A long horizontal metallic rod with length along the east-est direction is falling under gravity. The potential difference between its two ends will

1. Be zero
2. Be constant
3. Increase with time
4. Decrease with time

Answer : C (Increase with time)

Question 46: A metal conductor of length 1 m rotates vertically about one of its end with angular velocity 5 rad s-1. If horizontal component of earth’s magnetic field is 0.2 x 10 -4 T, then the emf developed between the ends of the conductor is

1. 5 µ V
2. 5 mV
3. 50 µ V
4. 50 m V

Answer : C ( 50 µV)

Question 47: In a coil current falls from 5A to 0A in 0.2 s. If an average emf of 150 V is induced, then the self inductance of the coil is

1. 4 H
2. 2 H
3. 3 H
4. 6 H

Answer : D ( 6 H)

Question 48: An infinitely long cylinder is kept parallel to a uniform magnetic field B directed along positive z axis. The direction of induced current on the surface of cylinder as seen from the z axis will be

1. Clockwise of the positive z axis
2. Anticlockwise of the positive z axis
3. Zero
4. Along the magnetic field

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