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 9 of 30
- A. The circuit behaves as a capacitive circuit.
- B. XC > XL
- C. Current leads the voltage.
- D. All of the above
Explanation: When the frequency is below resonance, Xc is greater than XL , which defines the circuit as capacitive.
Correct answer: All of the above- A. 100%
- B. 50%
- C. 99.9%
- D. 70%
Explanation: According to the maximum power transfer theorem, maximum power is delivered from a source to a load when the load resistance equals the…
Correct answer: 50%- A. Resonance
- B. Not in resonance
- C. Not possible
- D. None of the above
Explanation: This question relates to the maximum power transfer theorem. If the RLC circuit itself is considered the "load" for a source, maximum…
Correct answer: Resonance- A. Rheostat
- B. Potential divider
- C. Thermistor
- D. Resistor
Explanation: A choke coil is used to limit or control current in an AC circuit with minimal power loss.
Correct answer: Rheostat- A. Energy stored per cycle
- B. Energy dissipated per cycle
- C. The ratio of energy stored to energy dissipated per cycle
- D. Power loss
Explanation: The Quality Factor (Q) of a resonant circuit is a measure of its "quality" or sharpness of resonance.
Correct answer: The ratio of energy stored to energy dissipated per cycle166. A choke coil has.
- A. High inductance and high resistance
- B. Low inductance and low resistance
- C. High inductance and low resistance
- D. Low inductance and high resistance.
Explanation: A choke coil is designed to impede AC current effectively while minimizing energy loss.
Correct answer: High inductance and low resistance- A. ωL/R
- B. 1/ωRC
- C. √LC
- D. L/R
Explanation: The Quality Factor (Q) for a series RLC circuit at resonance is defined as the ratio of the reactance of the inductor (or capacitor) to…
Correct answer: ωL/R- A. This scenario is impossible.
- B. No electromagnetic wave is passing through the region.
- C. An electromagnetic wave may be passing through the region.
- D. An electromagnetic wave is certainly passing through the region.
Explanation: A defining characteristic of an electromagnetic wave is that the electric field, the magnetic field, and the direction of propagation are…
Correct answer: No electromagnetic wave is passing through the region.- A. Energy
- B. Charge
- C. Information
- D. Momentum
Explanation: Electromagnetic waves are propagating disturbances in electric and magnetic fields; they are composed of photons.
Correct answer: Charge- A. When the electric field is changing in the circuit
- B. When the magnetic field is changing in the circuit
- C. In both types of fields
- D. Through wires and resistance only
Explanation: Displacement current was proposed by Maxwell and is not a flow of charge, but rather a term proportional to the rate of change of electric…
Correct answer: When the electric field is changing in the circuit- A. Magnetic field
- B. Electric field
- C. An e.m.f
- D. Pressure radiant
Explanation: This is a cornerstone of Maxwell's equations (specifically, the Maxwell-Ampere law).
Correct answer: Magnetic field- A. 0 V
- B. 9.56 V
- C. 10.6 V
- D. 19.1 V
Explanation: The average value of any complete sinusoidal waveform (like AC voltage or current) over one full cycle is zero.
Correct answer: 0 V- A. 1
- B. Greater than 1
- C. Less than 1
- D. Zero
Explanation: In a purely inductive circuit, the current and voltage are 90° out of phase.
Correct answer: Zero- A. 100 Hz
- B. 200 Hz
- C. 400 Hz
- D. 800 Hz
Explanation: The general form for a sinusoidal current is I = I_peak sin(ωt), where ω is the angular frequency.
Correct answer: 100 Hz- A. 10.6 Ω
- B. 12.6 Ω
- C. 15.8 Ω
- D. 20.4 Ω
Explanation: Impedance Z = √(R² + XL^2 ), where R = 10 Ω, X = ωL = 2πfL = 2π × 50 × 0.02 = 6.28 Ω. Thus, Z = √(10² + 6.28²) = √(100 + 39.44) ≈ 12.6 Ω.
Correct answer: 12.6 Ω- A. 4 A
- B. 6 A
- C. 8 A
- D. 10 A
Explanation: At resonance, Z = R = 15 Ω (since XL = XC ). Current I = V/R = 120/15 = 8 A.
Correct answer: 8 A- A. Increases
- B. Decreases
- C. Remains same
- D. Becomes zero
Explanation: The resonant frequency of an RLC series circuit is:fo=1/2pisqrt {LC}Here, is inductance and is capacitance.If L increases, the denominator…
Correct answer: Decreases- A. 0 W
- B. 100 W
- C. 200 W
- D. 400 W
Explanation: A pure inductor consumes no average power (power factor cosφ = 0, as phase difference is 90°). Thus, P = VI cosφ = 0W.
Correct answer: 0 W- A. 50 Hz
- B. 75 Hz
- C. 100 Hz
- D. 125 Hz
Explanation: Resonant frequency f = 1/(2π√(LC)) = 1/(2π√(0.05 × 40 × 10⁻⁶)) ≈ 112.5 Hz, closest to 100 Hz.
Correct answer: 100 Hz- A. 4.8 A
- B. 6.4 A
- C. 8.2 A
- D. 10.4 A
Explanation: For resistor, IR = V/R = 120/15 = 8 A. For capacitor, Xc = 1/(2π × 50 × 60 × 10⁻⁶) ≈ 53.05 Ω, Ic= V/Xc = 120/53.05 ≈ 2.26 A.
Correct answer: 8.2 A