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 8 of 30
- A. 300%
- B. 200%
- C. 100%
- D. None
Explanation: Average power P (avg) = (I (peak) × V (peak) )/2. If both I (peak) and V (peak) are doubled, the new average power P' (avg) = (2I (peak) ×…
Correct answer: 300%- A. 2 times
- B. 3 times
- C. 4 times
- D. None
Explanation: The frequency of the instantaneous power in an AC circuit is always double the frequency of the voltage and current.
Correct answer: 2 times- A. Zero
- B. Infinite
- C. Finite
- D. None
Explanation: A pure or ideal inductor is a theoretical component that has only inductance and no resistance or capacitance.
Correct answer: Zero- A. Inductance
- B. Reactance
- C. Conductance
- D. None
Explanation: The formula for inductive reactance is XL = 2πfL. This is a linear equation of the form y = mx, where y=XL and x=f.
Correct answer: Inductance- A. Doubles
- B. Quadrupled
- C. Tripled
- D. None
Explanation: A DC source has a frequency of zero. The concept of "doubling" a zero frequency is not meaningful.
Correct answer: None- A. Constant inductance
- B. Decreasing inductance
- C. Increasing inductance
- D. None
Explanation: The graph of inductive reactance (XL) versus frequency (f) is a straight line passing through the origin. The slope of this line is 2πL.
Correct answer: Constant inductance- A. Low pass filter
- B. Medium pass filter
- C. High pass filter
- D. None
Explanation: An inductor's reactance (XL = 2πfL) increases with frequency. This means it offers little opposition to low-frequency signals but blocks…
Correct answer: Low pass filter- A. Doubles
- B. Halves
- C. Quadruples
- D. None
Explanation: For a purely resistive load, the resistance is an intrinsic property of the material and its geometry.
Correct answer: None149. In an inductor
- A. Emf leads the current by 90°
- B. Current leads the voltage by 90°
- C. Both are in phase
- D. None
Explanation: In a purely inductive AC circuit, the voltage (or EMF) across the inductor is maximum when the rate of change of current is maximum.
Correct answer: Emf leads the current by 90°- A. Low pass filter
- B. High pass filter
- C. Both A and B
- D. None
Explanation: A capacitor's reactance (Xc = 1/(2πfC)) decreases as frequency increases.
Correct answer: High pass filter- A. Current
- B. Voltage
- C. Resistance
- D. None
Explanation: When connected to a DC source, a capacitor allows a brief transient current to flow until it is fully charged.
Correct answer: None- A. The circuit is dissipating maximum power
- B. The circuit may or may not be dissipating maximum power
- C. The circuit is not dissipating any power
- D. None of the above
Explanation: A power factor of 1 means the circuit is purely resistive, and the voltage and current are in phase.
Correct answer: The circuit is dissipating maximum power153. As the inductive reactance in an R-L series AC circuit increases, which of the following is correct?
- A. Power factor is decreasing
- B. XL is increasing, indicating inductive behavior dominance
- C. Energy storing ability increases
- D. All of the above
Explanation: An increase in inductive reactance (XL) means the circuit is more inductive.
Correct answer: All of the above- A. Increases
- B. Decreases
- C. Same
- D. None
Explanation: Introducing a soft iron core greatly increases the solenoid's inductance (L).
Correct answer: Decreases- A. Inductance
- B. Capacitance
- C. Resistance
- D. All of the above
Explanation: The power factor is the cosine of the phase angle φ, where tan(φ) = (XL - Xc)/R.
Correct answer: All of the above- A. The impedance is minimum
- B. The voltage across the inductor (VL) can be greater than the applied voltage
- C. The voltage across the capacitor (VC) can be greater than the applied voltage
- D. All of the above
Explanation: At series resonance, impedance is at its minimum (Z=R), allowing maximum current.
Correct answer: All of the above- A. Two
- B. Three
- C. Four
- D. Infinite
Explanation: The resonance frequency is determined by the formula f = 1 / (2π√LC). There are infinitely many different pairs of values for L and C that…
Correct answer: Infinite- A. Doubled
- B. Quadrupled
- C. Tripled
- D. Halved
Explanation: The resonant frequency depends on the product LC. To keep the frequency constant, the product LC must also remain constant.
Correct answer: Halved- A. 4L, C/4
- B. 2C, 2L
- C. 4L, 4C
- D. 2L, 4C
Explanation: Resonance depends on the product of L and C. In option A, the new product L'C' = (4L)(C/4) = LC.
Correct answer: 4L, C/4- A. Inductive
- B. Capacitive
- C. Resistive
- D. None
Explanation: At frequencies below resonance, the capacitive reactance (Xc = 1/2πfC) is larger than the inductive reactance (XL = 2πfL).
Correct answer: Capacitive