61. What is the expression for voltage in the given circuit?
A. V = 60e − 0.5t
B. V = 30e − 0.5t
C. V = 60e − 2t
D. V = 30e − 2t
Answer: C
Applying KVL in above circuit, we get
60 − 30i − 15di/dt = 0
i = 2(1 − e − 2t)A
di/dt = 4e − 2t
V = Ldi/dt = 15 × 4e − − 2t = 60e − 2t.
62. At a steady-state, the current in the inductor is?
A. Maximum
B. Minimum
C. Zero
D. Infinity
Answer: A
At a steady-state maximum current flows in the inductor because it acts as an open circuit.
63. Initially, when the switch in a series RL circuit is closed, the inductor acts as?
A. Open circuit
B. Short circuit
C. Resistor
D. Capacitor
Answer: A
Before the switch is closed, the current in the inductor is zero. When the switch in a series RL circuit is closed, the current in the inductor remains zero since the current in the inductor doesn’t change suddenly. So, the inductor acts as an open circuit.
64. Initially, when the switch in a series RL circuit is closed, the current in the inductor is?
A. Maximum
B. Minimum
C. Zero
D. Infinity
Answer: C
Initially, when the switch in a series RL circuit is closed, the inductor acts as an open circuit. The current in an open circuit is zero, hence the inductor current is zero.
65. If the current in a coil having a constant inductance of L henrys grows at a uniform rate, what is the value of the average current?
A. I
B. I/2
C. I/4
D. 0
Answer: B
If the current in a coil having a constant inductance of L henrys grows at a uniform rate, the value of the average current is I/2.
The average current is the average of the current that flows in the inductor. Hence it is I/2.
66. What is the power in the magnetic field if the current in a coil has a constant inductance of L henrys grows at a uniform rate?
A. LI/2t
B. LI2/2t
C. L/2It
D. L/2I2t
Answer: B
EMF induced in the coil is Ldi/dt.
Energy = ei × dt
= Lidi/dt × dt = Li2/2.
Power = Energy/Time = Li2/2t.
67. What is the energy stored in the magnetic field if the current in a coil has a constant inductance of L henrys grows at a uniform rate?
A. LI/2
B. LI2/2
C. L/2I
D. L/2I2
Answer: B
EMF induced in the coil is Ldi/dt.
Energy = ei × dt = Lidi/dt × dt = Li2/2.
68. Find the average current in an inductor if the total current in the inductor is 26A.
A. 10 A
B. 26 A
C. 13 A
D. 5 A
Answer: C
Average current = I/2.
Substituting the value of I from the equation, average current = 13A.
69. Calculate the power in an inductive circuit if the inductance is 10H, and the current flowing in the inductor is 2A in 4s.
A. 50 W
B. 4 W
C. 5 W
D. 10 W
Answer: C
The expression for power in an inductive circuit is:
P = LI2/2t
Substituting the values from the given question, we get P = 5W.
70. Calculate the value of stored energy in an inductor if the value of inductance is 20H and 4A of current flows through it.
A. 220 J
B. 150 J
C. 190 J
D. 160 J
Answer: D
The expression for energy in an inductor is
E = LI2/2.
Substituting the values from the given question, we get E = 160J.
