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

1. 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.

2. What is Helmholtz equation?

a) i=I(1-e^{Rt/L})

b) i=I(1-e^{-Rt/L})

c) i=I(1+e^{-Rt/L})

d) i=I(e^{-Rt/L})

View Answer

Explanation: Helmholtz equation is an equation which gives the formula for the growth in an inductive circuit. Hence the Helmholtz formula is: i=I(1-e

^{-Rt/L}).

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

a) 1s

b) 2s

c) 0.5s

d) 5s

View Answer

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

Time constant= L/R

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

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

a) 5A

b) 10A

c) 15A

d) 20A

View Answer

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

I=V/R= 5A.

5. A coil has a resistance of 4 ohms and an inductance of 2H. It is connected to a 20V dc supply. Calculate the value of current 1s after the switch is closed.

a) 5.44A

b) 4.32A

c) 6.56A

d) 2.34A

View Answer

Explanation: We know that:

i=I(1-e

^{Rt/L})

I=V/R=5A

Substituting the remaining values from the given question, we get i=4.32A.

6. 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

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

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

7. 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.

8. 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.

9. 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.

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

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