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

Explanation: An R-L network is a network which consists of a resistor which is connected in series to an inductor.

2. At DC, inductor acts as _____________

a) Open circuit

b) Short circuit

c) Resistor

d) Inductor

View Answer

Explanation: At DC, the inductor acts as a short circuit because the inductive resistance is zero. The frequency of a DC circuit is 0. The inductive resistance=(2*pi*f*L). Therefore, if the frequency is 0, the inductive resistance is zero and it acts as a short circuit.

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

Explanation: 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 closes at t=0, what is the current in the circuit?

a) 0A

b) 10A

c) 20A

d) 30A

View Answer

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.

5. What is the voltage across the inductor at t=0?

a) 0V

b) 20V

c) 60V

d) 58V

View Answer

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.

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(e^{2t})A

d) i=2(1+e^{-2t})A

View Answer

Explanation: At t = 0+ the current in the circuit is zero. Therefore at t = 0+, i = 0, 0 = c + 2, c = -2. Substituting the value of c in the current equation, we have i = 2(1-e

^{-2t})A.

7. At steady state, inductor acts as ____________

a) Open circuit

b) Short circuit

c) Resistor

d) Capacitor

View Answer

Explanation: At steady state, inductor acts as a short circuit because at steady state maximum current flows across the inductor. Hence it acts as a zero resistance source or an open circuit.

8. At steady state, the current in the inductor is?

a) Maximum

b) Minimum

c) Zero

d) Infinity

View Answer

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

Explanation: Initially, when the switch in a series RL circuit is closed, the inductor acts as an open circuit. This is because the current gradually increases as time increases. At t=0, the current in the inductor is zero, hence it 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

View Answer

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.**

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