71. Calculate the emf induced in an inductor if the inductance is 10H and the current is 2A in 4s.
A. 2.5V
B. 1.5V
C. 3.5V
D. 5V
Answer: D
The expression for emf in an inductive circuit is:
emf = LdI/dt
Substituting the values from the given question, we get emf = 5V.
72. Calculate the value of emf in an inductor if the value of inductance is 15H and an average current of 5A flows through it in 10s.
A. 15V
B. 7.5V
C. 10V
D. 5.5V
Answer: B
The expression for emf in an inductive circuit is:
emf = LdI/dt
Substituting the values from the given question, we get emf = 7.5V.
73. Calculate the current in an inductor if the energy stored in 160J and the inductance is 20H.
A. 1A
B. 2A
C. 3A
D. 4A
Answer: D
The expression for energy in an inductor is:
E = LI2/2
Substituting the values from the given question, we get I = 4A.
74. Find the time taken for the current in an inductor to change to 2A from 0A if the power in the inductor is 5W. The value of inductance is 10H.
A. 1s
B. 2s
C. 3s
D. 4s
Answer: D
The expression for power in an inductive circuit is:
P = LI2/2t
Substituting the values from the given question, we get t = 4s.
75. The phenomenon due to which there is an induced current in one coil due to the current in a neighboring coil is?
A. Electromagnetism
B. Susceptance
C. Mutual inductance
D. Steady current
Answer: C
When there is a current in a coil, due to the magnetic field caused by the current there is current induced in the neighboring coil as well. This is known as mutual inductance.
76. If the current in one coil becomes steady, the current in the neighboring coil is?
A. Zero
B. Infinity
C. Doubles
D. Halves
Answer: A
A current is induced when there is changing magnetic flux. Hence the induced current in the neighboring coil is zero when the current is steady.
77. If the current in one coil is steady, what happens to the mutual inductance?
A. Zero
B. Infinity
C. Doubles
D. Halves
Answer: A
A current is induced when there is changing magnetic flux. The induced current in the neighboring coil is zero when the current is steady. So, mutual inductance is zero.
78. What is the SI unit of mutual inductance?
A. Ohm
B. Henry
C. Volt
D. Siemens
Answer: B
Mutual inductance is the inductance between the two neighboring coils. Since it is a type of inductance, its unit is that of inductance, that is, henry.
79. Which among the following is the correct expression for mutual inductance?
A. M = N2φ2/I2
B. M = N2φ2/I1
C. M = N1φ2/I2
D. M = N1φ1/I1
Answer: B
Mutual inductance is the product of the number of turns in one coil and the flux linkages of that coil, divided by the current in the other coil.
Hence M = N2φ2/I1 is the correct expression.
80. If the flux linkage in coil 1 is 3Wb and it has 500 turns and the current in coil 2 is 2A, calculate the mutual inductance.
A. 750H
B. 500H
C. 450H
D. 900H
Answer: A
We know that mutual inductance is the product of the number of turns in one coil and the flux linkages of that coil, divided by the current in the other coil.
