100 Electromagnetism MCQ with Explanation – Objective Question Answer for Electromagnetism Quiz

61. What happens to the current in a coil while accelerating a magnet inside it?

A. Increases
B. Decreases
C. Remains constant
D. Reverses

Answer: A

A change in the magnetic field induces an emf. When there is an emf, there has to be current. Hence, when the magnet is moved inside a coil, the current in it increases.

 

63. What is the consequence of the motor effect?

A. Current
B. Voltage
C. Electromagnetic induction
D. EMF

Answer: C

The motor effect is when a current-carrying conductor in a magnetic field experiences a force, hence its consequence is electromagnetic induction.

 

64. The total number of magnetic field lines passing through an area is termed as?

A. Voltage
B. EMF
C. Magnetic flux
D. Magnetic flux density

Answer: C

The number of magnetic field lines passing through an area is magnetic flux.

Magnetic flux: The number of magnetic field lines passing through a surface area normally is called magnetic flux. It is denoted by ϕ.

Magnetic flux is mathematically equal to the dot product of the magnetic field and area vector through which it is passing.

 

65. The formula for induced emf if magnetic field, length, and velocity of conductor all are mutually perpendicular is __________

A. emf = B2l
B. emf = Bil
C. emf = Blv
D. emf = B2v

Answer: C

The formula for induced emf is emf = Blv,

where

B is the magnetic field,

l is the length of the conductor

v is the velocity with which it is moving in the magnetic field and all three quantities are mutually perpendicular to each other.

 

66. If a conductor 0.2m long moves with a velocity of 0.3m/s in a magnetic field of 5T, calculate the emf induced if the magnetic field, velocity, and length of the conductor are mutually perpendicular to each other.

A. 0.3V
B. 0.03V
C. 30V
D. 3V

Answer: A

The formula for induced emf is

emf = Blv

if B,l, and v are perpendicular to each other. Substituting the values of B, l, and v from the question, we get emf = 0.3V.

 

67. Find the length of a conductor which is moving with a velocity of 0.4m/s in a magnetic field of 8T, inducing an emf of 20V if the magnetic field, velocity, and length of the conductor are mutually perpendicular to each other.

A. 50m
B. 5m
C. 6.25m
D. 0.5m

Answer: C

The formula for induced emf is

emf = Blv if B, l, and v are perpendicular to each other.

Substituting the values of B, emf, and v from the question, we get

20 = 8 × 0.4 × l

= 6.25m.

 

68. Find the strength of the magnetic field in a conductor 0.5m long moving with a velocity of 10m/s, inducing an emf of 20V if the magnetic field, velocity, and length of the conductor are mutually perpendicular to each other.

A. 1 T
B. 2 T
C. 3 T
D. 4 T

Answer: D

The formula for induced emf is

emf = Blv if B, l, and v are perpendicular to each other.

Substituting the values of l, emf, and v from the question, we get

20 = B × 10 ×  0.5

B = 4T.

 

69. What does emf stand for?

A. Electronic magnetic force
B. Electromotive force
C. Electromagnetic force
D. Electromated force

Answer: B

Emf stands for electromotive force. It is the voltage developed by any source of electrical energy.

 

70. What is emf (Electromagnetic Force)?

A. Force
B. Voltage
C. Current
D. Flux

Answer: B

Electromotive force is not actually a force. It is basically a voltage. It is the voltage developed by any source of electrical energy.

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