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.
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.
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
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?
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
Explanation: We know that:
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?
Explanation: The instantaneous voltage can be written in terms of the maximum voltage in the following manner:
Since i=v/R, we can write, i=Vm(sint)/R.
7. Can ohm’s law be applied in an ac circuit?
c) Depends on the rms current
d) Depends on the rms voltage
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)/XL
b) i = Vm(cost)/XL
c) i = -Vm(sint)/XL
d) i = -Vm(cost)/XL
I=V/XL = -Vm(cost)/XL (since current lags voltage by 900 in inductive circuit).
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