1. An RL network is one which consists of ____________
A. Resistor and capacitor in parallel
B. Resistor and capacitor in series
C. Resistor and inductor in parallel
D. Resistor and inductor in series
Answer: D
An R − L network is a network that consists of a resistor that is connected in series to an inductor.
2. If the switch is opened at t = 0, what is the current in the circuit?
A. 0A
B. 1A
C. 2A
D. 3A
Answer: C
Initially, when the switch was closed, the current in the inductor was 60/30 = 2A.
The current in the inductor doesn’t change suddenly so when the switch is opened, the current in the inductor remains the same i.e. 2A.
3. In an RL series circuit, when the switch is closed and the circuit is complete, what is the response?
A. Response does not vary with time
B. Decays with time
C. Increases with time
D. First increases, then decrease
Answer: B
In an RL series circuit, the response decays with time because according to the equation, there is an exponential decrease in the response.
4. If the switch is closed at t = 0, what is the current in the circuit?
A. 0A
B. 10A
C. 20A
D. 30A
Answer: A
Initially, when the switch is open, the current in the circuit is 0. As soon as the switch is closed at t = 0+, the inductor acts as an open circuit, hence the current in the circuit is zero. Since the current in the circuit is zero, there is no voltage drop across the resistor and hence the voltage across the inductor is equal to the supply voltage, i.e. 60V.
5. What is the voltage across the inductor at t = 0?
A. 0V
B. 20V
C. 60V
D. 58V
Answer: C
Initially, when the switch is open, the current in the circuit is 0. As soon as the switch is closed at t = 0+, the inductor acts as an open circuit, hence the current in the circuit is zero. Since the current in the circuit is zero, there is no voltage drop across the resistor and the voltage across the inductor is equal to the supply voltage, which is equal to 60V.
6. What is the expression for current in the given circuit?
A. i = 2(e − 2t)A
B. i = 2(1 − e − 2t)A
C. i = 2(e2t)A
D. i = 2(1+e − 2t)A
Answer: B
Applying KVL in above circuit, we get
60 − 30i − 15di/dt = 0
i = 2(1 − e − 2t)A
7. 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.
8. 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.
9. 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.
10. 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.
