Basic Electrical Engineering Questions and Answers – Growth in an Inductive Circuit

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

1. In a pure inductive circuit, the power factor is?
a) Maximum
b) Minimum
c) 0
d) Infinity
View Answer

Answer: c
Explanation: In a pure inductive circuit, the current is lagging by 90 degrees from the voltage. The power factor is the cosine of the angle between the voltage and the current. If the angle between the voltage and the current is 90, then cos90=0. Hence, the power factor is zero.
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2. Among the following, which is the right formula for growth in an inductive circuit?
a) VL=V(1-e-tR/L)
b) VL=(e-tR/L)
c) VL=(1-e-tR/L)
d) VL=V(e-tR/L)
View Answer

Answer: d
Explanation: The correct formula for growth in an inductive circuit is VL=V(e-tR/L). As the time increases, voltage decreases.

3. 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

Answer: c
Explanation: We know that: V=V0(1-e-tR/L).
When time constant=t, we have: V=V0(1-e-1) = 0.37*V0.
Hence the time constant is the time taken for the charge in an inductive circuit to become 0.37 times its initial charge.
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4. What is the time constant of an inductive circuit?
a) LR
b) R/L
c) 1/LR
d) L/R
View Answer

Answer: d
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.

5. 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

Answer: a
Explanation: We know that: Time constant = L/R
Substituting the values from the given question, we get a time constant = 2s.
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6. Calculate the resistance in an inductive circuit whose time constant is 2s and the inductance is 10H.
a) 7ohm
b) 10ohm
c) 2ohm
d) 5ohm
View Answer

Answer: d
Explanation: We know that: Time constant = L/R
Substituting the values from the given question, we get R=5ohm.

7. Calculate the inductance in an inductive circuit whose time constant is 2s and the resistance is 5 ohm.
a) 10H
b) 20H
c) 5H
d) 15H
View Answer

Answer: a
Explanation: We know that: Time constant = L/R
Substituting the values from the given question, we get L=10H.
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8. The charging time constant of a circuit consisting of an inductor is the time taken for the current in the inductor to become __________% of the initial current.
a) 33
b) 63
c) 37
d) 36
View Answer

Answer: b
Explanation: We know that: i=i0(1-e-tR/L).
When t=L/R, we have: i=i0(1-e-1) = 0.63*i0.
Hence the time constant is the time taken for the current in an inductive circuit to become 0.63 times its initial current.

Sanfoundry Global Education & Learning Series – Basic Electrical Engineering.

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

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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