This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Analysis of Decay”.

1. What is the time constant of an inductive circuit?

a) LR

b) R/L

c) 1/LR

d) L/R

View Answer

Explanation: The time constant in an inductive circuit is the time taken for the voltage across the inductor to become 63 percent of its initial value. It is given by: Time constant= L/R.

2. Among the following, which is the right formula for decay in an inductive circuit?

a) i=I(1-e^{-t}/time constant)

b) i=I(1-e^{t} /time constant)

c) i=(1-e^{-t} /time constant)

d) i=I(e^{-t} /time constant)

View Answer

Explanation: The correct formula for decay in an inductive circuit is i=I(e-t /time constant). As the time increases, the current in the inductor decreases, the voltage also increases.

3. The discharging time constant of a circuit consisting of an inductor is the time taken for the voltage in the inductor to become __________% of the initial voltage.

a) 33

b) 63

c) 37

d) 36

View Answer

Explanation: We know that: V=V0(e

^{-t}/time constant).

When time constant=t, we have: V=V0(e

^{-1})= 0.36*V0.

Hence the time constant is the time taken for the charge in an inductive circuit to become 0.36 times its initial charge.

4. A coil has a resistance of 4 ohm and an inductance of 2H. Calculate its time constant.

a) 1s

b) 2s

c) 0.5s

d) 5s

View Answer

Explanation: The expression for time constant in an inductive circuit is:

Time constant= L/R

Substituting the values from the question given, we get time constant= 0.5s.

5. In case of Inductive circuit, Frequency is ______________ to the current.

a) Directly proportional

b) Inversely proportional

c) Unrelated

d) Much greater than

View Answer

Explanation: Inductance is inversely proportional to current since, as the inductance increases, current decreases.

6. Calculate the time constant of an inductive circuit having resistance 5 ohm and inductance 10H.

a) 2s

b) 4s

c) 5s

d)10s

View Answer

Explanation: We know that: Time constant= L/R

Substituting the values from the given question, we get time constant= 2s.

7. Calculate the inductance in an inductive circuit whose time constant is 2 and the resistance is 5 ohm.

a) 10H

b) 20H

c) 5H

d) 15H

View Answer

Explanation: We know that: Time constant= L/R

Substituting the values from the given question, we get L=10H.

8. A coil has a resistance of 4 ohm and an inductance of 2H. It is connected to a 20V dc supply. Calculate the final value of current in the circuit.

a) 5A

b) 10A

c) 15A

d) 20A

View Answer

Explanation: The final value of current in the circuit is:

I=V/R= 5A.

9. What happens to the inductance when the current in the coil becomes double its original value?

a) Becomes half

b) Becomes four times

c) Becomes infinity

d) Becomes double

View Answer

Explanation: The formula for magnetic field strength in a coil is:

H=iN/l

The inductance is: directly proportional to magnetic field strength, hence as the current value doubles, the inductance also doubles.

10. What is the total applied voltage in an inductive circuit?

a) V=Ri+Ldi/dt

b) V=Ri+di/dt

c) V=i+Ldi/dt

d) V=R+Ldi/dt

View Answer

Explanation: The total voltage in an inductive circuit is the sum of the voltage due to the resistor which is Ri and the voltage due to the inductor which is Ldi/dt. Hence V=Ri+Ldi/dt.

**Sanfoundry Global Education & Learning Series – Basic Electrical Engineering.**

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