Growth and decay current in LR circuit MCQ [Free PDF] – Objective Question Answer for Growth and decay current in LR circuit Quiz

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

Answer: A

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(eRt/L)
B. i = I(1 − e − Rt/L)
C. i = I(1+e − Rt/L)
D. i = I(e − Rt/L)

Answer: B

Helmholtz equation is an equation that 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. It is connected to a 20V dc supply. Calculate the initial value of the current in the circuit.

A. 5A
B. 10A
C. 0 A
D. 20A

Answer: C

Initially, the inductor behaves as an open circuit for dc current so, i = 0.

 

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

Answer: A

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

Answer: B

We know that:

i = I(1 − eRt/L)

I = V/R = 5A

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

 

6. 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 voltage 1s after the switch is closed.

A. 5.4V
B. 10.8V
C. 0 V
D. 2.7V

Answer: D

V = V0e − Rt/L

V = 20e − 2 = 2.7V.

 

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 − et /time constant)
C. i = (1 − e − t /time constant)
D. i = I(e − t /time constant)

Answer: D

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 and 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

Answer: C

We know that: V = V0(e − tR/L).

When t = L/R

we have: V = V0(e − 1) = 0.37 × V0.

Hence the time constant is the time taken for the voltage in an inductive circuit to become 0.37 times its initial voltage.

 

9. A coil has a resistance of 4 ohms and an inductance of 2H. It is connected to a 20V dc supply. Calculate the initial value of the voltage across the inductor.

A. 5V
B. 10V
C. 0 V
D. 20V

Answer: D

Initially, the inductor behaves as an open circuit for dc current so, V = V0 = 20V i.e. same as a voltage source.

 

10. 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 voltage across the inductor.

A. 5V
B. 10V
C. 0 V
D. 20V

Answer: C

At a steady-state, the inductor behaves as a short circuit for dc current so, V = 0

Scroll to Top