Free Alternating Current MCQs with Answers
592 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.
Alternating current varies periodically, so phase relationships become essential when current passes through a resistor, capacitor or inductor. The chapter distinguishes resistance from capacitive and inductive reactance, explains phase lead and lag, and connects changing electric and magnetic fields with the production and properties of electromagnetic waves.
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Read the Alternating Current notesFree MDCAT chapter notes with key terms592 questions · page 28 of 30
- A. they both become zero.
- B. they both become infinite.
- C. the voltage leads the current.
- D. the current leads the voltage.
Explanation: * The question explicitly states, "the waveform of the current lags behind it [voltage]." This directly means that the voltage is ahead of…
Correct answer: the voltage leads the current.- A. 220 V
- B. 400 V
- C. 440 V
- D. 1100 V
Explanation: In a three-phase alternating current supply, the voltage across any two power lines is typically 400 V.
Correct answer: 400 V- A. 0°
- B. 90°
- C. 120°
- D. 240°
Explanation: In a three-phase AC generator, each of the three phases is separated by 120°.
Correct answer: 120°544. 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.
Correct answer: 120°- A. Proportional to (frequency)2
- B. Proportional to frequency
- C. Proportional to (frequency)½
- D. Independent to frequency
Explanation: a) Proportional to (frequency)^2:The rate of production of heat in a pure resistor, when connected to an alternating potential difference…
Correct answer: Proportional to (frequency)2- A. 2.2mA
- B. 2.2/√2 mA
- C. 2.2 x √2 mA
- D. None of the above
Explanation: By Ohm's law; V=IRIrms = Vrms/R = 220/100x10(3) = 2.2x10(-3) A= 2.2mA
Correct answer: 2.2mA- A. Mechanical waves
- B. Sound waves
- C. Tidal waves
- D. Electromagnetic waves
Explanation: Waves that do not require any medium for their propagation are called electromagnetic waves.
Correct answer: Electromagnetic waves- A. Electric field
- B. Magnetic field
- C. Both Options A and B are correct
- D. None of these options is correct
Explanation: Remember that x-rays and gamma rays cannot be deflected by electric and magnetic fields.
Correct answer: None of these options is correct- A. UV
- B. IR
- C. X-rays
- D. Gamma-rays
Explanation: The UV light from Sun is converted to IR as it interacts with the Earth's surface and this IR is then trapped by green house gases such as…
Correct answer: IR- A. Resonance
- B. Resistance.
- C. Current.
- D. None of these.
Explanation: When the frequency of the transmitted wave matches the one displayed on the radio, which is done by tuning it, the amplitude of the sound…
Correct answer: Resonance- A. R is large, L is very small
- B. R is very small, L is large
- C. Both R and L are large
- D. Both R and L are very small
Explanation: In an ideal choke, a coil should have almost zero internal resistance, R≈0, if a coil has resistance it will consume power.Since R needs…
Correct answer: R is very small, L is large- A. Capacitance
- B. Inductance
- C. Charge
- D. Resistance
Explanation: The correct answer is Inductance. In the context of electrical systems, inductance is analogous to mass because both properties determine…
Correct answer: Inductance- A. Natural resonance
- B. Mechanical resonance
- C. Free resonance
- D. Electrical resonance
Explanation: Tuning a radio is the best example of electrical resonance. When we turn the knob of a radio to tune a station, we are changing the…
Correct answer: Electrical resonance- A. 3 x 10^5 ms-1
- B. 3 x 10^3 ms-1
- C. 3 x 10^6 ms-1
- D. 3 x 10^8 ms-1
Explanation: Explanation:The speed of light, radio waves, and microwaves in the vaccum is the same, which is approximately 3 × 108 m/s.
Correct answer: 3 x 10^8 ms-1- A. 2.45 GHz
- B. 2452 Hz
- C. 2456 Hz
- D. 2455 Hz
Explanation: The electromagnetic waves used in a microwave oven have a frequency of 2.45 x 10° Hz.
Correct answer: 2.45 GHz- 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…
Correct answer: 3π/2- A. 10 joule
- B. 0.1 joule
- C. 0.01 joule
- D. 1.0 joule
Explanation: Using the formula for energy stored in magnetic field of a coil (E = ½ × L × I²)E = ½ × L × I² E = ½ × (50 × 10-3) × (2)² = 0.1 J
Correct answer: 0.1 joule- A. The voltage leads current by 900
- B. The voltage leads current by 1800
- C. The current leads voltage by 900
- D. The current and voltage are in phase
Explanation: In A.C capacitive circuits, the current leads the voltage by 90° because first, the current flows through the two plates of the capacitor…
Correct answer: The current leads voltage by 900- A. P > V°l°
- B. <P>= V°I° sinθl°
- C. <P>= V°I° Cos θl
- D. <P>= zero
Explanation: In purely inductive or purely capacitive circuit, power loss is zero.
Correct answer: <P>= zero- A. By increasing the frequency of AC
- B. By decreasing the frequency of AC
- C. Does not depend upon the frequency of the AC voltage
- D. None of these
Explanation: Capacitive reactance (Xc) is inversely proportional to the frequency of the AC voltage.
Correct answer: By decreasing the frequency of AC