Free Alternating Current MCQs with Answers

• A. 0.65
• B. 0.75
• C. 0.85
• D. 0.95

Explanation: XL = 2π × 50 × 0.03 ≈ 9.42 Ω. Impedance Z = √(12² + 9.42²) ≈ √(144 + 88.74) ≈ 15.2 Ω.

• A. 3.5 A
• B. 4.5 A
• C. 5.5 A
• D. 6.5 A

Explanation: Xc = 1/(2π × 60 × 120 × 10⁻⁶) ≈ 22.1 Ω. Impedance Z = √(35² + 22.1²) ≈ √(1225 + 488.41) ≈ 41.4 Ω.

• A. 5.5 A
• B. 6.5 A
• C. 7.5 A
• D. 8.5 A

Explanation: At resonance, Z = R = 20 Ω. Current I = V/R = 150/20 = 7.5 A.

• A. 9.5 A
• B. 10.5 A
• C. 11.5 A
• D. 12.5 A

Explanation: For resistor, IR = 110/10 = 11 A. For capacitor, Xc = 1/(2π × 50 × 40 × 10⁻⁶) ≈ 79.58 Ω, I = 110/79.58 ≈ 1.38 A.

• A. 10.5 Ω
• B. 11.3 Ω
• C. 12.7 Ω
• D. 14.2 Ω

Explanation: Impedance Z = √(R² + X ), where XL = ωL, ω = 2πf = 2π × 60 ≈ 376.8 rad/s. XL = 376.8 × 0.02 = 7.536 Ω.

• A. 2.36 A
• B. 3.77 A
• C. 4.52 A
• D. 5.89 A

Explanation: Capacitive reactance Xc = 1 / (ωC) = 1 / (2π × 50 × 100 × 10⁻⁶) ≈ 31.83 Ω. Irms = Vrms / Xc = 120 / 31.83 ≈ 3.77 A.

• A. 15.2°
• B. 67.8°
• C. 36.9°
• D. 45.0°

Explanation: ω = 2π × 60 ≈ 376.8 rad/s. XL = ωL = 376.8 × 0.05 ≈ 18.84 Ω.Xc = 1 / (ωC) . = 1 / (376.8 × 40 × 10⁻⁶) ≈ 66.35 Ω.

• A. 50 Hz
• B. 79.6 Hz
• C. 100 Hz
• D. 159.2 Hz

Explanation: Power factor cos φ = 0.707 implies φ = 45°, so XL = R = 30 Ω. XL = ωL = 2πf × 0.06 = 30, f = 30 / (2π × 0.06) ≈ 30 / 0.377 ≈ 79.6 Hz.

• A. 63.7 Hz
• B. 100.0 Hz
• C. 159.2 Hz
• D. 200.0 Hz

Explanation: Resonant frequency f = 1 / (2π √(LC)) = 1 / (2π √(0.1 × 25 × 10⁻⁶)) = 1 / (2π √(2.5 × 10⁻⁴)) = 1 / (2π × 0.01581) ≈ 159.2 Hz.

• A. Voltage
• B. Current
• C. Impedance
• D. Reactance

Explanation: In a series RLC circuit, resonance occurs when the inductivereactance equals the capacitive reactance.At this resonant frequency:The…

• A. Must be positive
• B. Never be positive
• C. May or may not be positive
• D. None

Explanation: In an AC circuit, power refers to the average rate of energy dissipation.

• A. Emf leads the current by 90°
• B. Current leads the voltage by 90°
• C. Both are in phase
• D. None

Explanation: In an AC circuit, an inductor causes the current to lag behind the voltage because it resists changes in current.

• A. 0.5 x 10^-3 sec
• B. 0.5 Sec
• C. 5 sec
• D. 2 sec

Explanation: The time period T is the reciprocal of frequency 𝑓 : T = 1/𝑓 = 1 / 2x10 = 0.5 x 10-3 seconds.

• A. Vrms/√2
• B. √2Vrms
• C. 2/√2 Vrms
• D. 2√2 Vrms

Explanation: The correct answer is 2√2 Vrms. In an AC circuit, the RMS value is a measure of the effective value of an alternating current or voltage.

• A. √2 Io
• B. 2 Io
• C. Io
• D. 0.7 Io

Explanation: This means that the root mean square (RMS) value of a current with a peak value of Io is obtained by multiplying the peak value by the…

• A. Ammeter (D.C)
• B. Moving coil galvanometer
• C. Hot wire ammeter
• D. All of the above

Explanation: Hot wire ammeter, refers to a device specifically designed to measure alternating current (AC) accurately by passing the current through a…

• A. π /2√2
• B. π /2
• C. √2 π
• D. 2√2 π

Explanation: It represents the form factor for a sine wave when considering the peak value divided by the average value.

• A. Dynamo
• B. Motor
• C. Transformer
• D. Rectifier

Explanation: "Rectifier," is a device that converts alternating current (AC) to direct current (DC) by allowing current to flow in only one direction.

• A. Xc=VI
• B. Xc=V/I
• C. Xc=I/V
• D. Xc=1/2πfC

Explanation: The correct option represents the capacitive reactance, which is the opposition to the flow of alternating current in a circuit due to a…

• A. Time period
• B. Critical time
• C. frequency of AC
• D. None of the above

Explanation: :The correct option, "Time period," refers to the duration it takes for an AC voltage source to change its polarity once, moving from…