LUMS LCAT Physics: Electromagnetic Induction MCQs

LUMS LCAT Physics: Electromagnetic Induction MCQs — sample questions

1. Question 1

   Q1. A coil of 100 turns is rotated in a magnetic field, inducing an emf of 10 V. If rotation rate doubles, induced emf becomes

   • A) 5 V
   • B) 10 V
   • C) 20 V
   • D) 40 V

   Answer: 20 V

   Explanation: Induced emf is directly proportional to rate of change of flux, hence doubling rotation rate doubles induced emf.

2. Question 2

   Q2. The magnetic flux linked with a coil is given by φ = 5t² + 2t + 3. Induced emf at t = 1 s is

   • A) 10 V
   • B) 12 V
   • C) 15 V
   • D) 20 V

   Answer: 12 V

   Explanation: Induced emf = -dφ/dt = -(10t + 2), at t = 1 s, emf = -12 V.

3. Question 3

   Q3. A conducting rod of length 1 m moves with a velocity of 5 m/s in a magnetic field of 0.1 T. Induced emf is

   • A) 0.1 V
   • B) 0.5 V
   • C) 1 V
   • D) 5 V

   Answer: 0.5 V

   Explanation: Induced emf = Blv = 0.1 * 1 * 5 = 0.5 V.

4. Question 4

   Q4. The self-inductance of a coil is 2 H. If current changes from 0 to 5 A in 1 / 2 s, induced emf is

   • A) 10 V
   • B) 20 V
   • C) 40 V
   • D) 80 V

   Answer: 20 V

   Explanation: Induced emf = -L(dI/dt) = -2 * (5 / 0.5) = -20 V.

5. Question 5

   Q5. A coil of inductance 1 H and resistance 10 ohm is connected to a 10 V battery. Energy stored in the coil is

   • A) 0.1 J
   • B) 0.5 J
   • C) 1 J
   • D) 5 J

   Answer: 0.5 J

   Explanation: Energy stored = 1/2 * LI² = 1/2 * 1 * (10/10)² = 0.5 J.

6. Question 6

   Q6. The mutual inductance between two coils is 0.5 H. If current in one coil changes from 0 to 2 A in 1 s, induced emf in the other coil is

   • A) 0.5 V
   • B) 1 V
   • C) 2 V
   • D) 4 V

   Answer: 1 V

   Explanation: Induced emf = -M(dI/dt) = -0.5 * (2 / 1) = -1 V.

7. Question 7

   Q7. A rectangular coil of 100 turns, area 0.1 m², is rotated at 50 rev/s in a magnetic field of 0.01 T. Maximum induced emf is

   • A) 10π V
   • B) 20π V
   • C) 30π V
   • D) 40π V

   Answer: 10π V

   Explanation: Maximum emf = NAB ω with ω = 2πf. Here f = 50, so ω = 100π. NAB = 100 × 0.1 × 0.01 = 0.1. Emf = 0.1 × 100π = 10π V.

8. Question 8

   Q8. The magnetic flux through a coil is φ = 3t² + 4t + 9. The induced emf at t = 2 s is

   • A) 12 V
   • B) 16 V
   • C) 20 V
   • D) 24 V

   Answer: 16 V

   Explanation: Induced emf = -dφ/dt = -(6t + 4), at t = 2 s, emf = -16 V.

9. Question 9

   Q9. A coil of self-inductance 0.5 H has a current of 2 A. If the current is reduced to zero in 0.1 s, induced emf is

   • A) 5 V
   • B) 10 V
   • C) 15 V
   • D) 20 V

   Answer: 10 V

   Explanation: Induced emf = -L(dI/dt) = -0.5 * (-2 / 0.1) = 10 V.

10. Question 10

    Q10. Two coils have a mutual inductance of 0.01 H. If current in one coil changes at a rate of 100 A/s, induced emf in the other coil is

    • A) 0.1 V
    • B) 1 V
    • C) 10 V
    • D) 100 V

    Answer: 1 V

    Explanation: Induced emf = -M(dI/dt) = -0.01 * 100 = -1 V.

11. Question 11

    Q11. The energy stored in an inductor is proportional to

    • A) I
    • B) I²
    • C) 1/I
    • D) 1/I²

    Answer: I²

    Explanation: Energy stored = 1/2 * LI², hence proportional to I².

12. Question 12

    Q12. A coil has 500 turns and is rotated in a magnetic field. If the flux linked with the coil changes from 0 to 1 Wb in 1 s, induced emf is

    • A) 250 V
    • B) 500 V
    • C) 750 V
    • D) 1000 V

    Answer: 500 V

    Explanation: Induced emf = N(dφ/dt) = 500 * (1 / 1) = 500 V.

13. Question 13

    Q13. The self-inductance of a coil is given by L = μN²A/l. If number of turns is doubled, self-inductance becomes

    • A) 2L
    • B) 4L
    • C) 8L
    • D) L/2

    Answer: 4L

    Explanation: L is proportional to N², hence doubling N makes L four times.

14. Question 14

    Q14. The induced emf in a coil is maximum when the angle between the coil and magnetic field is

    • A) 0°
    • B) 45°
    • C) 90°
    • D) 180°

    Answer: 90°

    Explanation: Induced emf = NABωsin(ωt), maximum when ωt = 90°.

15. Question 15

    Q15. A coil is placed in a magnetic field such that its plane is perpendicular to the field. The coil is rotated by 90°. Change in flux is

    • A) 0
    • B) BA
    • C) -BA
    • D) 2BA

    Answer: BA

    Explanation: Initial flux = BA, final flux = 0, hence change in flux = BA.

16. Question 16

    Q16. The time constant of an L-R circuit is 2 s. If the inductance is 1 H, resistance is

    • A) 0.5 ohm
    • B) 1 ohm
    • C) 2 ohm
    • D) 4 ohm

    Answer: 0.5 ohm

    Explanation: Time constant = L/R, hence R = L / time constant = 1 / 2 = 0.5 ohm.

17. Question 17

    Q17. A conducting loop is placed in a magnetic field. If the loop is shrinking, induced emf is

    • A) Zero
    • B) Non-zero
    • C) Alternating
    • D) Constant

    Answer: Non-zero

    Explanation: Changing area induces an emf.

18. Question 18

    Q18. The emf induced in a coil rotating in a magnetic field is maximum when

    • A) coil is parallel to field
    • B) coil is perpendicular to field
    • C) rate of change of flux is maximum
    • D) rate of change of flux is minimum

    Answer: rate of change of flux is maximum

    Explanation: Induced emf is maximum when rate of change of flux is maximum.

19. Question 19

    Q19. Two coils are placed close to each other. If the current in one coil is changed, the emf induced in the other coil is due to

    • A) self-inductance
    • B) mutual inductance
    • C) capacitance
    • D) resistance

    Answer: mutual inductance

    Explanation: Mutual inductance is the phenomenon of inducing emf in one coil due to change in current in another coil.

20. Question 20

    Q20. A coil is connected to a battery. The current in the coil is

    • A) maximum at t = 0
    • B) maximum at t = ∞
    • C) minimum at t = 0
    • D) constant for all t

    Answer: maximum at t = ∞

    Explanation: In an L-R circuit, current grows exponentially and becomes maximum at t = ∞.