AC Power MCQs

Practice AC Power MCQs with four options, answers and explanations for focused Electronics & Telecommunication Engineering revision.

Question 1

Network TheoryAC Power

A coil has resistance 6 ohm and inductive reactance 8 ohm. Its impedance magnitude and power factor are respectively?

A10 ohm and 0.6
B14 ohm and 0.8
C10 ohm and 0.8
D2 ohm and 0.6

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Correct Answer: A. 10 ohm and 0.6

Explanation: |Z|=√(6^2+8^2)=10 ohm. Power factor = R/|Z| = 6/10 = 0.6 lagging.

Reference: Standard network theory: ac power

Question 2

Network TheoryAC Power

A load consumes 800 W at a power factor of 0.8 lagging. Its apparent power is?

A640 VA
B800 VA
C1000 VA
D1250 VA

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Correct Answer: C. 1000 VA

Explanation: Apparent power S = P/pf = 800/0.8 = 1000 VA.

Reference: Standard network theory: ac power

Question 3

Network TheoryAC Power

A load has apparent power 1000 VA and real power 600 W. The magnitude of reactive power is?

A400 var
B600 var
C800 var
D1600 var

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Correct Answer: C. 800 var

Explanation: Using S^2=P^2+Q^2, Q=√(1000^2-600^2)=800 var.

Reference: Standard network theory: ac power

Question 4

Network TheoryAC Power

For a load with lagging power factor, power-factor correction is commonly achieved by connecting?

AA capacitor in parallel with the load
BAn additional resistor in series only
CA DC voltage source in parallel
DAn open circuit

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Correct Answer: A. A capacitor in parallel with the load

Explanation: A shunt capacitor supplies leading reactive power that offsets part of the load's lagging reactive power.

Reference: Standard network theory: ac power

Question 5

Network TheoryAC Power

A load has apparent power 5 kVA and real power 4 kW. Its reactive power magnitude is?

A1 kVAR
B2 kVAR
C3 kVAR
D4 kVAR

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Correct Answer: C. 3 kVAR

Explanation: Using S^2=P^2+Q^2, Q=sqrt(5^2-4^2)=3 kVAR.

Reference: Standard network theory: reactive power numerical

Question 6

Network TheoryAC Power

A load draws 10 A RMS from a 200 V RMS supply at power factor 0.6 lagging. Its real power is?

A600 W
B1200 W
C1600 W
D2000 W

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Correct Answer: B. 1200 W

Explanation: P=VI cos(phi)=200×10×0.6=1200 W.

Reference: Standard network theory: single-phase real power numerical

Question 7

Network TheoryAC Power

For the same 200 V, 10 A, 0.6 lagging load, the reactive power magnitude is?

A800 var
B1200 var
C1600 var
D2000 var

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Correct Answer: C. 1600 var

Explanation: sin(phi)=sqrt(1-0.6^2)=0.8, so Q=VI sin(phi)=200×10×0.8=1600 var.

Reference: Standard network theory: single-phase reactive power numerical

Question 8

Network TheoryAC Power

A load consumes 3 kW and 4 kVAR. Its apparent power magnitude is?

A1 kVA
B5 kVA
C7 kVA
D12 kVA

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Correct Answer: B. 5 kVA

Explanation: |S|=sqrt(P^2+Q^2)=sqrt(3^2+4^2)=5 kVA.

Reference: Standard network theory: complex power triangle numerical

Question 9

Network TheoryAC Power

For a sinusoidal steady-state circuit, complex power S is conventionally written as?

AP-jQ
BP+jQ
CQ+jP
DP/Q

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Correct Answer: B. P+jQ

Explanation: Complex power is S=P+jQ, where P is average real power and Q is reactive power.

Reference: Standard network theory: complex power

Question 10

Network TheoryAC Power

A load has complex power S=3+j4 kVA. Its power factor is?

A0.4 lagging
B0.6 lagging
C0.8 lagging
D1.0

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Correct Answer: B. 0.6 lagging

Explanation: |S|=5 kVA and power factor=P/|S|=3/5=0.6. Positive Q denotes an inductive, lagging load.

Reference: Standard network theory: complex power factor numerical

Question 11

Network TheoryAC Power

A load has complex power S=4-j3 kVA. Its power factor characteristic is?

A0.8 leading
B0.8 lagging
C0.6 leading
D0.6 lagging

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Correct Answer: A. 0.8 leading

Explanation: |S|=5 kVA, so pf=4/5=0.8. Negative reactive power indicates capacitive behavior, hence leading power factor.

Reference: Standard network theory: leading power factor