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 7 of 30
- A. 1
- B. 0
- C. -1
- D. 0.5
Explanation: At resonance, the inductive and capacitive reactances cancel each other out, making the circuit purely resistive.
Correct answer: 1- A. R
- B. XL
- C. Xc
- D. None of the above
Explanation: The total impedance of a series RLC circuit is Z = √(R² + (XL - Xc)²). At the resonant frequency, inductive reactance (XL) equals…
Correct answer: R- A. 100 Hz
- B. 80 Hz
- C. 50 Hz
- D. 120 Hz
Explanation: Inductive reactance is given by X = 2πfL. Rearranging to solve for frequency gives f = X / (2πL).
Correct answer: 80 Hz- A. 5.07 pF
- B. 50 pF
- C. 0.507 pF
- D. 507 pF
Explanation: The resonant frequency is f = 1 / (2π√LC). Rearranging to solve for capacitance gives C = 1 / (4π²f²L).
Correct answer: 507 pF- A. 180°
- B. 90°
- C. 0°
- D. None of these
Explanation: At resonance, the inductive and capacitive reactances cancel, making the circuit behave as if it were purely resistive.
Correct answer: 0°- A. 9.4 kHz
- B. 940 kHz
- C. 94 kHz
- D. None of these
Explanation: The frequency of a wave is the number of cycles (or vibrations) per second, measured in Hertz (Hz).
Correct answer: 94 kHz- A. In the resistor, I leads V by 90°-In the capacitor, I leads V by 90°
- B. In the resistor, I lags V by 90° - In the capacitor, I leads V by 90°
- C. In the resistor, I and V are in phase - In the capacitor, I leads V by 90°
- D. In the resistor, I and V are in phase - In the capacitor, I lags V by 90°
Explanation: In a resistor, voltage and current stay in phase. In a capacitor, current leads voltage by 90° because the capacitor must charge before…
Correct answer: In the resistor, I and V are in phase - In the capacitor, I leads V by 90°- A. A rectifier
- B. A detector
- C. An oscillator
- D. An amplifier
Explanation: Amplification is the process of increasing the strength of a signal. A diode is a passive component that cannot provide the power gain…
Correct answer: An amplifier- A. 20 V
- B. 10 V
- C. 5 V
- D. 25 V
Explanation: Here is the correct answer with a clean, brief theoretical explanation: Answer: 5 V Brief explanation ; In a series RLC circuit at…
Correct answer: 5 V- A. Step-up
- B. Step-down
- C. Primary
- D. Secondary
Explanation: In a transformer, when the number of turns in the secondary coil (Ns) is greater than the number of turns in the primary coil (Np), the…
Correct answer: Step-up- A. The potential of a conductor increases when the charge on it decreases, but this affects the charge stored in it.
- B. The potential of a conductor is greatly reduced when the charge on it increases.
- C. The potential of a conductor increases without affecting the charge stored in it.
- D. The potential of a conductor increases as the charge on it increases.
Explanation: A capacitor stores charge by maintaining a potential difference between two conductors.
Correct answer: The potential of a conductor increases as the charge on it increases.132. If the output frequency of A.C generator is increased by a factor of 2 then output frequency of <p>?
- A. 2 times
- B. 3 times
- C. 4 times
- D. None
Explanation: In an A.C. generator, the frequency of induced e.m.f/current i s directly proportional to the frequency of rotation of the g enerator.
Correct answer: 2 times- A. 0
- B. Constant
- C. Positive
- D. Max
Explanation: A complete AC cycle consists of a positive half-cycle and a negative half-cycle that are perfectly symmetrical.
Correct answer: 0- A. 50%
- B. 44%
- C. 41.4%
- D. 30%
Explanation: The RMS value is V (rms) = V (peak)/ √2 ≈ 0.707 V (peak) . The difference is V (peak) - 0.707 V (peak) = 0.293 V (peak) .
Correct answer: 41.4%- A. The current is high
- B. The current is low
- C. Voltage is high
- D. The voltage is low
Explanation: A capacitor filter works well only when load current is low. Low current means the capacitor discharges slowly.
Correct answer: The current is low- A. Chemical effect
- B. Heating effect
- C. Magnetic effect
- D. None
Explanation: The heating effect (P = I²R) depends on the square of the current, making it independent of direction.
Correct answer: Heating effect- A. Must be positive
- B. Never can be positive
- C. May or may not be positive
- D. None
Explanation: Power loss in a resistor is due to the conversion of electrical energy into heat (P = I²R).
Correct answer: Must be positive- A. 1:2
- B. 2:1
- C. 1:1
- D. None
Explanation: In a resistive AC circuit, the average power is P (avg) = I (rms) × V (rms) = (I (peak) /√2) × (V (peak) /√2) = (I (peak) × V (peak) )/2.
Correct answer: 1:2- A. 100 watts
- B. 200 watts
- C. 282.84 watts
- D. None
Explanation: The average power is P (avg) = I (rms) × V (rms) = 100 W. The peak power is P (peak) = I (peak) × V (peak) .
Correct answer: 200 watts- A. 100%
- B. 200%
- C. 50%
- D. No change
Explanation: Peak power P = I (peak) × V (peak) . Assuming voltage is constant, if I (peak) is doubled, the new power P' = (2I (peak) )V (peak)= 2P.
Correct answer: 100%