This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Alternating Current in a Resistive & Inductive Circuit”.

1. Instantaneous voltage is the product of resistance and _____________ current in a resistive circuit.

a) Instantaneous

b) Average

c) RMS

d) Peak

View Answer

Explanation: V=IR. So, V(t)=i(t)R

Instantaneous voltage is the product of resistance and instantaneous current in a resistive circuit.

2. Find the value of the instantaneous voltage if the resistance is 2 ohm and the instantaneous current in the circuit is 5A.

a) 5V

b) 2V

c) 10V

d) 2.5V

View Answer

Explanation: We know that,

v=iR, substituting the given values from the question, we get v=10V.

3. The power for a purely resistive circuit is zero when?

a) Current is zero

b) Voltage is zero

c) Both current and voltage are zero

d) Either current or voltage is zero

View Answer

Explanation: P=VIcosϕ Power in a circuit is the product of voltage, current and the cosine of the phase angle. Phase angle is 00 for 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 instantaneous voltage is Vm(sint) in a resistive circuit is?

a) 1A

b) 2A

c) 3A

d) 4A

View Answer

Explanation: 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

View Answer

Explanation: We know that:

R=V/I

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

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

View Answer

Explanation: 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 current

d) Depends on the rms voltage

View Answer

Explanation: 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)/X_{L}

b) i = Vm(cost)/X_{L}

c) i = -Vm(sint)/X_{L}

d) i = -Vm(cost)/X_{L}

View Answer

Explanation: V=Vm*sint

I=V/X

_{L}= -Vm(cost)/X

_{L}(since current lags voltage by 900 in inductive circuit).

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