Power in a circuit is the product of voltage, current, and the cosine of the phase angle.

The phase angle is 00 for a purely resistive circuit so, P = VI.

Hence if either voltage or current is zero, the power is zero.

4. The correct expression for the instantaneous current if the instantaneous voltage is Vm(sint) in a resistive circuit is?

A. 1A
B. 2A
C. 3A
D. 4A

Answer: B

We know that: V = Vm(sint)

Since i = V/R,

we can write, i = Vm(sint)/R.

5. Calculate the resistance in the circuit if the RMS voltage is 20V and the RMS current is 2A.

A. 2 ohm
B. 5 ohm
C. 10 ohm
D. 20 ohm

Answer: C

We know that:

R = V/I

Substituting the given values from the question, we get R = 10 ohm.

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6. The correct expression for the instantaneous current in a resistive circuit is?

A. i = Vm(sint)/R
B. i = Vm(cost)/R
C. i = V(sint)/R
D. i = V(cost)/R

Answer: A

The instantaneous voltage can be written in terms of the maximum voltage in the following manner:

v = Vm(sint)

Since i = v/R

we can write, i = Vm(sint)/R.

7. Can ohm’s law be applied in an ac circuit?

A. Yes
B. No
C. Depends on the RMS’s current
D. Depends on the RMS voltage

Answer: A

Ohm’s law can be applied in ac as well as dc circuits. It can be applied in ac circuits because the condition V = IR holds true even in ac circuits.

8. The correct expression for the instantaneous current if instantaneous voltage is Vm(sint) in an inductive circuit is?

A. i = Vm(sint)/XL
B. i = Vm(cost)/XL
C. i = -Vm(sint)/XL
D. i = -Vm(cost)/XL

Answer: D

V = Vm × sint

I = V/XL = -Vm(cost)/XL (since current lags voltage by 900 in inductive circuit).

9. Inductor does not allow sudden changes in?

A. Voltage
B. Current
C. Resistance
D. Inductance

Answer: B

The inductor does not allow sudden changes in current because if current changes in the inductor occur in zero time, the voltage becomes zero which is not possible.

10. Inductance is __________ to number of turns in the coil.

A. directly proportional
B. inversely proportional
C. equal
D. not related

Answer: A

L = µ0N^{2}A/l

Inductance is directly proportional to the number of turns in the coil.