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Free Phase of Alternating Current MCQs with Answers

29 Phase of Alternating Current MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

Phase describes the position of an alternating voltage or current within its cycle and the phase difference between two sinusoidal quantities. The topic covers in phase signals, phase angle and lead or lag in resistive, inductive and capacitive circuits, rather than the amplitude or frequency of the supply.

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29 questions · page 2 of 2

21. In a three phase alternating current (AC) generator, the voltage generated across the third pair of coils with reference to slip rings has a phase of

  • A. 0°
  • B. 90°
  • C. 120°
  • D. 240°

Explanation: In a three-phase AC generator, each of the three phases is separated by 120°.

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Correct answer: 120°

22. The phase difference between each pair of coils of a three phase alternating current generatoris

  • A. 0°
  • B. 60°
  • C. 120°
  • D. 180°

Explanation: A three-phase alternating current generator produces three waveforms that are 120° out of phase with each other.

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Correct answer: 120°

23. The phase at negative peak of AC voltage is:

  • A. π/2
  • B. π
  • C. 3π/2
  • D. 2π/3

Explanation: Given the AC voltage is in the form of a sinusoidal wave starting from 0, the positive peak is at π/2 and thus the negative peak is at…

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Correct answer: 3π/2

24. The mean value of sinusoidal emf over cycle is:

  • A. Maximum
  • B. Zero
  • C. Maximum and minimum
  • D. No change in emf

Explanation: Zero: The mean value of a sinusoidal emf over a cycle is zero. This is because the positive and negative values of the sinusoidal wave…

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Correct answer: Zero

25. In alternating current the average value of current in the cycle is;

  • A. Zero
  • B. Constant
  • C. Positive
  • D. Maximum

Explanation: The average current value in a complete cycle of AC waveform, such as a sine wave, is zero because the positive and negative parts of the…

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Correct answer: Zero

26. The sinusoidal AC in a circuit is I = 50 sin (20 t). The peak value of the current is:

  • A. 100 A
  • B. 25 A
  • C. 50 A
  • D. 20 A

Explanation: The sinusoidal AC current given by the equation I = 50 sin(20t) has a peak value that is determined by the amplitude of the sine function.

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Correct answer: 50 A

27. Instantaneous emf at instant t is ε20 sin (100πt). The frequency of alternative current is

  • A. 100 Hz
  • B. 200Hz
  • C. 50 Hz
  • D. 150Hz

Explanation: If we compare the given equation with the formula V=Vosin(wt+ϕ),Vo=20, ϕ=0, w=100.

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Correct answer: 50 Hz

28. The peak value of alternating current is 5√2 A. The mean square value of current will be:

  • A. 5A
  • B. 2.5A
  • C. 5√2 A
  • D. 52 A

Explanation: The mean square value (RMS value) of the current is calculated as:RMS value = Peak value / √2= 5√2 / √2= 5 A Therefore, option a is correct.

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Correct answer: 5A

29. The domestic electricity supply has a frequency of

  • A. 150Hz
  • B. 50Hz
  • C. 100Hz
  • D. 200Hz

Explanation: In most countries, the domestic electricity supply, also known as the mains electricity or grid power, has a frequency of 50Hz (50 cycles…

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Correct answer: 50Hz
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