Alternating Current

Alternating Current MDCAT MCQs with answers

17 past paper MCQs from Physics unit 12, Alternating Current, across 3 topics. They are arranged topic by topic; bigger topics show a sample here and link to their full set and to study notes. Tap “Show answer” for the correct option and a short solution.

Practise as a quiz

Phase of Alternating Current

1.A phase difference of 90° is equal to: (UHS MDCAT 2025)

  1. π radians
  2. π/2 radians
  3. 2π radians
  4. π/4 radians
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Correct answer: (b) π/2 radians

A full cycle is $2\pi$ radians, so a quarter of it is $\pi/2$.

2.The domestic electricity supply has a frequency of: (PMC MDCAT 2020)

  1. 150 Hz
  2. 100 Hz
  3. 50 Hz
  4. 25 Hz
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Correct answer: (c) 50 Hz

Mains electricity in Pakistan is supplied at $50\,\mathrm{Hz}$.

A.C. Through a Resistor, a Capacitor and an Inductor

3.In a pure capacitance AC circuit, the current: (KMU MDCAT 2025)

  1. Lags behind voltage by 90°
  2. Leads the voltage by 90°
  3. Is in phase with the voltage
  4. Leads the voltage by 45°
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Correct answer: (b) Leads the voltage by 90°

A capacitor must be charged before a voltage appears across it, so the current runs a quarter cycle ahead.

4.If frequency of AC is doubled, the inductive reactance will: (SIBA MDCAT 2025)

  1. Remain same
  2. Be halved
  3. Be doubled
  4. Become zero
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Correct answer: (c) Be doubled

Inductive reactance is $2\pi fL$, so it is proportional to the frequency.

5.A capacitor is connected to an AC source. If the frequency of the AC source is doubled the current in a purely capacitive circuit will: (SZABMU MDCAT 2025)

  1. Be doubled
  2. Remains Unchanged
  3. Become Half
  4. Becomes zero
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Correct answer: (a) Be doubled

Capacitive reactance is $1/2\pi fC$, so twice the frequency halves it and doubles the current.

All 6 A.C. Through a Resistor, a Capacitor and an Inductor MCQs → A.C. Through a Resistor, a Capacitor and an Inductor notes →

The Electromagnetic Spectrum

6.The wave that has the highest frequency & penetrating power is: (UHS MDCAT 2025)

  1. X-rays
  2. Ultraviolet rays
  3. Gamma rays
  4. Microwaves
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Correct answer: (c) Gamma rays

Gamma rays sit at the top of the electromagnetic spectrum in frequency and penetrate the most.

7.Red light is used in photographic dark room because of: (SZABMU MDCAT 2023)

  1. More frequency, less wavelength
  2. Less frequency, less wavelength
  3. Less frequency, more wavelength
  4. More frequency, more wavelength
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Correct answer: (c) Less frequency, more wavelength

Red is at the low frequency, long wavelength end, so its photons carry too little energy to expose the film.

8.The direct exposure of sun light where ozone layer is depleted will cause: (PMC MDCAT 2022)

  1. Skin cancer
  2. Sugar
  3. Corona
  4. Sun burn
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Correct answer: (a) Skin cancer

The ozone layer absorbs the ultraviolet, and without it that radiation reaches the skin.

All 9 The Electromagnetic Spectrum MCQs → The Electromagnetic Spectrum notes →

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