This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Growth in an Inductive Circuit”.

1. 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.

2. In a pure inductive circuit, the power factor is?

a) Maximum

b) Minimum

c) 0

d) Infinity

View Answer

Explanation: In a pure inductive circuit, current is lagging by 90 degrees from the voltage. The power factor is the cosine of the angle in between the voltage and the current. If the angle between the voltage and current is 90, then cos90=0. Hence, the power factor is zero.

3. 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 dou-bles, the inductance also doubles.

4. Among the following, which is the right formula for inductance?

a) L=emf*t/I

b) L=emf/t*I

c) L=emf*I/t

d) L=emf*t*I

View Answer

Explanation: The average emf induced is proportional to the current per unit time, the constant of proportionality being L. Hence emf=LI/t. Making L the subject of the formula, we get: L=emf*t/I.

5. Among the following, which is the right formula for growth in an inductive circuit?

a) VL=V(1-e^{-t}/time constant)

b) VL=V(1-e^{t} /time constant)

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

d) VL=V(e^{-t} /time constant)

View Answer

Explanation: The correct formula for growth in an inductive circuit is VL=V(1-e

^{-t}/time constant). As the time increases, the current in the inductor increases hence the voltage also increases.

6. The charging 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(1-e

^{-t}/time constant).

When time constant=t, we have: V=V0(1-e

^{-1})= 0.63*V0.

Hence the time constant is the time taken for the charge in an inductive circuit to become 0.63 times its initial charge.

7. 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.

8. 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.

9. Calculate the resistance in an inductive circuit whose time constant is 2s-1 and the inductance is 10H.

a) 7ohm

b) 10ohm

c) 2ohm

d) 5ohm

View Answer

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

Substituting the values from the given question, we get R=5ohm.

10. Calculate the inductance in an inductive circuit whose time constant is 2s-1 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.

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

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