AC Circuits Study Materials for Competitive Exams

AC Circuits

Q. What is the phase difference between the voltage and current in a purely resistive AC circuit? (2021)

A. 0°
B. 45°
C. 90°
D. 180°

Solution

In a purely resistive circuit, the voltage and current are in phase, so the phase difference is 0°.

Correct Answer: A — 0°

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Q. What is the phase difference between the voltage and current in a series RLC circuit at resonance? (2023)

A. 0°
B. 90°
C. 180°
D. 45°

Solution

At resonance in a series RLC circuit, the phase difference between voltage and current is 0°.

Correct Answer: A — 0°

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Q. What is the power consumed in an AC circuit with a voltage of 230V and a current of 5A with a power factor of 0.8? (2023)

A. 920W
B. 1150W
C. 115W
D. 460W

Solution

Power = V × I × Power Factor = 230V × 5A × 0.8 = 920W.

Correct Answer: A — 920W

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Q. What is the power factor in a circuit with a resistance of 5 ohms and a reactance of 5 ohms? (2022)

A. 0
B. 0.5
C. 1
D. √2/2

Solution

Power factor = R/Z = 5/√(5² + 5²) = 5/√50 = √2/2.

Correct Answer: D — √2/2

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Q. What is the power factor in an AC circuit with a phase angle of 30 degrees? (2022)

A. 0.5
B. 0.866
C. 1
D. 0.707

Solution

The power factor is cos(30°) = √3/2 ≈ 0.866.

Correct Answer: B — 0.866

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Q. What is the power factor of a circuit with a resistance of 30Ω and a reactance of 40Ω? (2023)

A. 0.6
B. 0.75
C. 0.8
D. 1.0

Solution

Power factor = R/Z where Z = √(R² + X²). Calculate.

Correct Answer: A — 0.6

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Q. What is the power factor of a circuit with a resistance of 4Ω and a reactance of 3Ω? (2021)

A. 0.6
B. 0.8
C. 1.0
D. 0.75

Solution

Power factor = R/Z = R/√(R² + X²) = 4/√(4² + 3²) = 4/5 = 0.8.

Correct Answer: A — 0.6

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Q. What is the power factor of a circuit with a resistance of 5 ohms and a reactance of 5 ohms? (2022)

A. 0
B. 0.5
C. 1
D. √2/2

Solution

Power factor = R/Z = 5/√(5² + 5²) = 5/√50 = √2/2.

Correct Answer: D — √2/2

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Q. What is the power factor of a circuit with a resistance of 5Ω and an inductive reactance of 5Ω? (2022)

A. 0.5
B. 0.707
C. 1
D. 0

Solution

Power factor = R/Z = 5 / √(5² + 5²) = 5 / √50 = 0.707.

Correct Answer: B — 0.707

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Q. What is the power factor of a circuit with a resistance of 6Ω and a reactance of 8Ω? (2022)

A. 0.75
B. 0.8
C. 0.6
D. 1.0

Solution

Power factor = R/Z = R/√(R² + X²) = 6/√(6² + 8²) = 6/10 = 0.6.

Correct Answer: B — 0.8

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Q. What is the power factor of a circuit with a resistance of 8Ω and a reactance of 6Ω? (2023)

A. 0.5
B. 0.6
C. 0.8
D. 1.0

Solution

Power factor = R/Z, where Z = √(R² + X²) = √(8² + 6²) = 10. Thus, PF = 8/10 = 0.8.

Correct Answer: C — 0.8

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Q. What is the power factor of an AC circuit with a phase angle of 60°? (2022)

A. 0.5
B. 0.866
C. 1
D. 0.707

Solution

The power factor is cos(60°) = 0.5.

Correct Answer: B — 0.866

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Q. What is the total current in a circuit with a voltage of 240V, resistance of 20 ohms, and inductive reactance of 30 ohms? (2022)

A. 8 A
B. 6 A
C. 4 A
D. 10 A

Solution

Z = √(R² + Xl²) = √(20² + 30²) = √(400 + 900) = √1300 = 36.06 ohms. I = V/Z = 240/36.06 = 6.66 A.

Correct Answer: B — 6 A

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Q. What is the total current in a parallel circuit with two branches, one with 5A and the other with 3A? (2022)

A. 8A
B. 15A
C. 2.5A
D. 5A

Solution

Total current in parallel = I1 + I2 = 5A + 3A = 8A.

Correct Answer: A — 8A

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Q. What is the total current in a series circuit with a 10Ω resistor and a 20Ω inductor connected to a 100V AC source at 50Hz? (2023)

A. 2A
B. 4A
C. 5A
D. 10A

Solution

Total impedance Z = √(R² + (ωL)²) = √(10² + (2π(50)(20))²). Calculate to find current.

Correct Answer: B — 4A

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AC Circuits

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