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 2 of 30
- A. pi radians
- B. pi/2 radians
- C. 2 pi radians
- D. pi/4 radians
Explanation: A complete cycle is 360 degrees or 2 pi radians, so 90 degrees is a quarter of a cycle, that is pi over 2 radians.
Correct answer: pi/2 radians- A. X-rays
- B. Ultraviolet rays
- C. Gamma rays
- D. Microwaves
Explanation: Gamma rays sit at the extreme short wavelength end of the electromagnetic spectrum, so they carry the highest frequency and photon energy…
Correct answer: Gamma rays- A. Affect in charging a capacitor
- B. Affect in charging a battery
- C. Affect while passing through an inductance
- D. Heating effect through a resistance
Explanation: Both AC and DC produce thermal energy in a resistance, with the heating effect determined by power and, for AC, by the RMS current: P =…
Correct answer: Heating effect through a resistance- A. An analogue waveform
- B. Continuous wave form
- C. Electronic waveform
- D. A digital waveform
Explanation: A rectangular voltage switches between discrete levels, commonly high and low, so it is classified as a digital waveform.
Correct answer: A digital waveform25. The velocity of an oscillating charge as it moves to and fro along a wire is always_____________?
- A. constant
- B. zero
- C. changing
- D. infinite
Explanation: For an oscillating charge, velocity changes continuously in magnitude and reverses direction as the charge moves to and fro, so it is not…
Correct answer: changing- A. Radio
- B. Microwave oven
- C. Both in radio and microwave oven
- D. Neither in radio nor in a microwave oven
Explanation: A radio uses an LC tuning circuit in which inductive and capacitive reactances can become equal, producing electrical resonance and…
Correct answer: Radio- A. Its electric field
- B. Its coils
- C. Its magnetic field
- D. Both electric and magnetic fields
Explanation: An inductor stores energy in the magnetic field produced by current through its coils.
Correct answer: Its magnetic field- A. IA. V = VR+VL+VC
- B. V2 = VR2+VL2+VC2
- C. V2 = VR2+(VL-VC)2
- D. V2 = VL2+(VR-VC)2
Explanation: In a series LCR circuit, VR is in phase with the current, while VL and VC are 90° from it and opposite to each other.
Correct answer: V2 = VR2+(VL-VC)2- A. Zero
- B. 45°
- C. 90°
- D. 180°
Explanation: For a pure resistance, the voltage and current rise and fall together, so their phase difference is 0°.
Correct answer: Zero- A. Peak values of voltage and current
- B. Effective values of voltage and current
- C. Instantaneous values of voltage and current
- D. All of the above
Explanation: A resistor obeys v = iR at every instant, and the same proportionality also holds between peak values and between RMS values.
Correct answer: All of the above- A. 10mH
- B. 12mH
- C. 16mH
- D. 20mH
Explanation: A voltage-current phase angle of 45° gives tan 45° = XL/R = 1, so XL = 100 ohms.
Correct answer: 16mH- A. 1Ω
- B. 5Ω
- C. 7Ω
- D. 7Ω
Explanation: Resistance and inductive reactance are perpendicular components of impedance, so Z = √(R² + XL²) = √((4 ohms)² + (3 ohms)²) = √25 ohms² =…
Correct answer: 5Ω- A. Zero
- B. 2
- C. 1
- D. Not definite
Explanation: At resonance, the inductive and capacitive reactances are equal and cancel, so the circuit impedance is purely resistive.
Correct answer: 1- A. DC circuit
- B. AC circuits
- C. Both AC and DC circuit
- D. Full wave rectifier circuit
Explanation: A choke coil has high inductive reactance, XL = 2πfL, in an AC circuit and can limit current with relatively little power loss.
Correct answer: AC circuits- A. 220V
- B. 220/ 2V
- C. 110V
- D. 220 √2V
Explanation: The 220 V mains value is an RMS voltage. For a sinusoidal supply, Vpeak = √2 Vrms = √2 x 220 V = 220√2 V, approximately 311 V.
Correct answer: 220 √2V- A. Same
- B. Different
- C. At L will be more than at C
- D. At L will be less than at C
Explanation: Components connected in parallel have the same potential difference across their terminals, regardless of their different reactances.
Correct answer: Same- A. The exact value of the current
- B. RMS value of the current
- C. The net value of the current
- D. The peak value of the current
Explanation: A standard AC ammeter is calibrated to indicate the RMS value of alternating current, which produces the same heating effect as an…
Correct answer: RMS value of the current- A. Lags behind voltage by π/2
- B. Is in phase with voltage
- C. Opposite in phase of voltage by π
- D. Leads forward the voltage by π/2
Explanation: For a pure capacitor, current leads the voltage by π/2, or 90 degrees, because current is proportional to the rate at which voltage…
Correct answer: Leads forward the voltage by π/239. When A.C current passes through a capacitor then the current relationship will be_______________?
- A. The current lead voltage by phase angle is 90 degrees
- B. The voltage leads current by phase angle is 90 degrees
- C. The current lead voltage by phase angle is 45 degrees
- D. The voltage leads current by phase angle is 45 degrees
Explanation: In a capacitive AC circuit, the current leads the voltage by 90 degrees because i = C(dV/dt), so current responds to the changing voltage.
Correct answer: The current lead voltage by phase angle is 90 degrees- A. Twice
- B. One half
- C. Four times
- D. None
Explanation: The LC resonance frequency is f = 1/(2π√(LC)). If capacitance becomes 4C, the denominator becomes √4 = 2 times larger, so the frequency…
Correct answer: One half