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Alternating Current MCQs for MDCAT Practice

Physics section, Alternating Current chapter. Up to eight free sample questions, each with the correct answer and a worked explanation. The full chapter opens in the app.

The bank has 655 active questions on this chapter. Your first 500 practice attempts are free, and every attempt includes a worked explanation.

  1. Question 1
    An alternating voltage V (in volts) is represented by the equation:V = 300 sin(100πt) What is the value of “f” for this voltage?
    • 100 Hz
    • 50 Hz (correct answer)
    • 25 H
    • 200 Hz
    Correct answer: B
    This question tests your understanding of the standard equation for alternating voltage and how to extract frequency from it.
  2. Question 2
    what is the quality factor of resistance?
    • Zero (correct answer)
    • ∞
    • Infinite
    • Maximum but finite
    Correct answer: A
    The quality factor (Q) of a purely resistive circuit is zero because it quantifies energy dissipation relative to energy storage, which is absent in resistance alone.
  3. Question 3
    The power factor of a purely capacitive circuit is:
    • 0 (correct answer)
    • 1
    • infinite
    • 0.5
    Correct answer: A
    In a purely capacitive AC circuit, current and voltage are 90° out of phase, resulting in zero average power and a power factor of 0.
  4. Question 4
    A heater marked 1000 W, 250 V is connected to a 220 V(rms) AC supply. Assuming it's purely resistive, calculate the actual power it consumes.
    • 880W
    • 774.4W (correct answer)
    • 950W
    • 1000W
    Correct answer: B
    Rated power isn't actual power when voltage changes. Calculate resistance first, then actual power using the new voltage.
  5. Question 5
    The effective value of alternating current is:
    • √2 times its maximum value
    • 1√2 times its maximum value (correct answer)
    • 2 times its maximum value
    • 1/2 times its maximum value
    Correct answer: B
    The effective (RMS) value of a sinusoidal AC is its peak value divided by √2, because it delivers the same average power as a DC current of that magnitude.
  6. Question 6
    The electromagnetic radiations are in descending order of wavelength in the following sequence:
    • Infra-red waves, radio waves, X-rays, visible light rays
    • Radio-waves, infra-red waves, visible light rays, X-rays (correct answer)
    • Radio waves, visible light rays, infra-red waves, X-rays
    • X-rays, visible light rays, infra-red wave, Radio-waves
    Correct answer: B
    Order electromagnetic waves by wavelength: Radio > IR > Visible > X-rays. This tests knowledge of the electromagnetic spectrum's ordering.
  7. Question 7
    How many times per second will an incandescent lamp reach maximum brilliances when connected to a 50Hz source?
    • 25 times (correct answer)
    • 50 times
    • 100 times
    • 200 times
    Correct answer: A
    An incandescent lamp's brightness fluctuates with AC frequency, reaching peak brilliance twice per cycle.
  8. Question 8
    Describe impedance as vector sum of resistances and reactances.
    • Impedance is the algebraic sum of resistance and reactance. (correct answer)
    • Impedance is the vector sum of resistance and reactance.
    • Impedance is the scalar sum of resistance and reactance.
    • Impedance is the arithmetic sum of resistance and reactance.
    Correct answer: A
    Impedance (Z) in AC circuits is the vector sum of resistance (R) and reactance (X), representing total opposition to current flow.

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Read the full Alternating Current chapter notes: Alternating Current notes. Or browse every chapter.