Free AC Through Resistor, Capacitor and Inductor MCQs with Answers
76 AC Through Resistor, Capacitor and Inductor 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 through a resistor, capacitor and inductor involves phase relationships between voltage and current, reactance, impedance and energy transfer. A resistor keeps voltage and current in phase, while a capacitor and inductor produce opposite phase shifts, a distinction used in circuit diagrams and numerical calculations.
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- A. in phase with each other
- B. 90 degrees out of phase, with current leading
- C. 90 degrees out of phase, with current lagging
- D. 180 degrees out of phase
Explanation: A resistor obeys Ohm's law at every instant, so the current peaks exactly when the voltage peaks and both pass through zero together.
Correct answer: in phase with each other- A. lags the voltage by 90 degrees
- B. leads the voltage by 90 degrees
- C. is in phase with the voltage
- D. is zero
Explanation: A capacitor must charge before a voltage can appear across it, so the current is greatest when the voltage is momentarily zero and falls…
Correct answer: leads the voltage by 90 degrees- A. increases as the frequency increases
- B. decreases as the frequency increases
- C. is independent of frequency
- D. is the same as resistance
Explanation: Reactance is one over 2 pi f C, so a capacitor passes high frequencies readily and blocks direct current entirely, since at zero frequency…
Correct answer: decreases as the frequency increases- A. 2 pi f L
- B. 1 divided by 2 pi f L
- C. L divided by 2 pi f
- D. 2 pi f divided by L
Explanation: Reactance rises in proportion to frequency, so a coil that passes direct current almost freely offers a large opposition at high…
Correct answer: 2 pi f L- A. maximum
- B. zero, because energy is stored and returned each quarter cycle
- C. equal to VI
- D. half of VI
Explanation: With a 90 degree phase difference the power is positive for one quarter cycle and equally negative for the next, so the net energy…
Correct answer: zero, because energy is stored and returned each quarter cycle- A. the impedance is maximum and the current minimum
- B. the impedance is minimum and equal to the resistance, so the current is maximum
- C. the current is zero
- D. the capacitor and inductor can be removed without effect
Explanation: At resonance the inductive and capacitive reactances are equal and cancel, leaving only the resistance to oppose the current, so the…
Correct answer: the impedance is minimum and equal to the resistance, so the current is maximum- A. the ratio of peak to rms current
- B. the cosine of the phase angle between current and voltage
- C. the ratio of frequency to reactance
- D. the product of voltage and current
Explanation: True power is V times I times cos theta, so the power factor measures how much of the apparent power is actually being converted to useful…
Correct answer: the cosine of the phase angle between current and voltage- A. is cheaper
- B. limits the current without dissipating energy as heat
- C. increases the voltage
- D. converts AC to DC
Explanation: An inductor opposes the current through reactance rather than resistance, and because the current and voltage are a quarter cycle out of…
Correct answer: limits the current without dissipating energy as heat- A. reactance only
- B. impedance
- C. capacitance
- D. inductance
Explanation: Impedance combines resistance and net reactance and is what relates the rms voltage to the rms current, being measured in ohms.
Correct answer: impedance- A. doubled
- B. halved
- C. unchanged
- D. quadrupled
Explanation: Power is conserved in an ideal transformer, so if the voltage doubles the current must halve to keep the product the same.
Correct answer: halved- 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 waveform13. 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: 5ΩAC Through Resistor, Capacitor and Inductor MCQs: common questions
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