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

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)

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

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

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

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

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)

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

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

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