Basic Electrical Engineering Questions and Answers – Transients in LR Networks

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This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Transients in LR Networks”.

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
View Answer

Answer: d
Explanation: An R-L network is a network which consists of a resistor which is connected in series to an inductor.
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2. If the switch is opened at t=0, what is the current in the circuit?
Find the current in the circuit if the switch is opened at t=0
a) 0A
b) 1A
c) 2A
d) 3A
View Answer

Answer: c
Explanation: Initially when switch was closed,current in the inductor was 60/30=2A.
Current in inductor doesn’t change suddenly so when switch is opened, current in inductor remains 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
View Answer

Answer: b
Explanation: In an RL series circuit, the response decays with time because according to the equation, there is an exponential decrease in the response.
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4. If the switch is closed at t=0, what is the current in the circuit?
Find the current in the circuit If the switch is opened at t=0
a) 0A
b) 10A
c) 20A
d) 30A
View Answer

Answer: a
Explanation: 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 voltage across the inductor is equal to the supply voltage, i.e. 60V.

5. What is the voltage across the inductor at t=0?
Find the voltage across the inductor at t=0 when the switch is open
a) 0V
b) 20V
c) 60V
d) 58V
View Answer

Answer: c
Explanation: Initially, when the switch is open, the current in the circuit is 0. As soon as the switch is closes 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.
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6. What is the expression for current in the given circuit?
Find 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
View Answer

Answer: b
Explanation: 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?
Find the expression for voltage in the given circuit by applying KVL
a) V=60e-0.5t
b) V=30e-0.5t
c) V=60e-2t
d) V=30e-2t
View Answer

Answer: c
Explanation: 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.
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8. At steady state, the current in the inductor is?
a) Maximum
b) Minimum
c) Zero
d) Infinity
View Answer

Answer: a
Explanation: At 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
View Answer

Answer: a
Explanation: Before switch is closed, current in inductor is zero. When the switch in a series RL circuit is closed, current in the inductor remains zero since current in inductor doesn’t change suddenly. So, the inductor acts as an open circuit.
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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
View Answer

Answer: c
Explanation: Initially, when the switch in a series RL circuit is closed, the inductor acts as an open circuit. Current in an open circuit is zero, hence the inductor current is zero.

Sanfoundry Global Education & Learning Series – Basic Electrical Engineering.

To practice all areas of Basic Electrical Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.

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