Electromagnetic Induction MCQs for NEETs

1 The magnetic flux (∅) lined with a coil is related to its area (s) as:

A ∅ ∝ s

B ∅ ∝ s²

C ∅ ∝ s^1/2

D ∅ ∝ s^-1/2

Answer:∅ ∝ s

2 If the magnetic flux linked with a coil through which a current off ampere is set up is ∅, then the coefficient of self-inductance of the coil is:

A l/∅

B ∅/l

C ∅l

D None of these

Answer & Explanation

Answer:∅/l

3 The magnetic flux (∅) linked with a coil is related to the number of turns (N) ofthe coil as:

A f ∝ N

B f ∝ N^-1

C f ∝ N²

D f ∝ N^-2

Answer & Explanation

Answer:f ∝ N

4 A transformer is used to light 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A. Then the efficiency of the transformer is:

A 11%

B 50%

C 80%

D 90%

Answer & Explanation

Answer:90%

5 An e^– and a p^– are moving parallel to each other in a magnetic field. The magnetic force acting on the p⁺ is:

A 1840 times that on e^–

B less than that of e^–

C same as that of e^–

D slightly more than that of e^–

Answer & Explanation

Answer:same as that of e^–

6 The magnetic field is parallel to a surface, then the magnetic flux through the surface is :

A zero

B small but not zero

C infinite

D large but not infinite

Answer & Explanation

Answer:small but not zero

7 In a uniform magnetic field B, a wire in the form of a semicircle of radius r rotated about the diameter of the circle with angular frequency ‘ω’. The axis of rotation is perpendicular to the field. If the total resistance of the circuit is R the mean power generated per period of rotation is :

A

B

C

D

Answer & Explanation

Answer:B

8 In the expression e = –d∅/dt, the -ve sign signifies:

A The induced emf is produced only when magnetic flux decreases

B The induced emf opposes the change in the magnetic flux

C The induced emf is opposite to the direction of the flux

D None of these

Answer & Explanation

Answer:The induced emf opposes the change in the magnetic flux

9 The coupling co-efficient of the perfectly coupled coils is:

A Zero

B 1

C slightly more than 1

D infinite

Answer & Explanation

Answer:1

10 The core of a transformer is laminated because:

A rusting of core may be prevented

B ratio of voltage in primary and secondary may be increased.

C energy losses due to eddy current may be minimised

D The weight of transformer may be reduced

Answer & Explanation

Answer:energy losses due to eddy current may be minimised

11 The flux linked with a coif at any instant t is given by ∅ = 10t² – 50t + 250. The induced emf at t = 35 is:

A 10 V

B 190 V

C -190 V

D -10 V

Answer & Explanation

Answer:-10 V

12 When the magnetic field is parallel to a surface, then the magnetic flux through the surface is:

A infinite

B zero

C small but not zero

D large but not infinite.

Answer & Explanation

Answer:zero

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

A 4 mH

B 16 mH

C 10 mH

D 6 mH

Answer & Explanation

Answer:10 mH

14 For purely capacitive circuits, power factor is:

A 0

B -1

C 1

D infinity

Answer & Explanation

Answer:0

15 A choke is used as a resistance in :

A dc circuits

B ac circuits

C both ac and dc circuits

D neither (a) nor (b)

Answer & Explanation

Answer:ac circuits

16 If I current is flowing inductance L, then the dimension of 3/2 LI² is equivalent to:

A charge

B force

C momentum

D energy

Answer & Explanation

Answer:momentum

17 A metal conductor of length 1 m rotates vertically about one of its ends at angular velocity 5 rad s^-1 . If the horizontal component of earth’s magnetism is 2 × 10^-5 T, then e.m.f. developed between the two ends of the conductor is:

A 5 µV

B 50 µV

C 5 mV

D 50 mV

Answer & Explanation