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.
Last updated
Read the Alternating Current notesFree MDCAT chapter notes with key terms592 questions · page 10 of 30
- A. 141.4 V
- B. 200 V
- C. 282.8 V
- D. 100 V
Explanation: RMS voltage Vrms = Vpeak/√2 = 200/√2 ≈ 141.4 V.
Correct answer: 141.4 V- A. 2.2 A
- B. 3.1 A
- C. 4.4 A
- D. 5.5 A
Explanation: For a purely resistive AC circuit, Irms = Vrms/R = 220/50 = 4.4 A .
Correct answer: 4.4 A- A. 31.4 Ω
- B. 62.8 Ω
- C. 94.2 Ω
- D. 125.6 Ω
Explanation: Inductive reactance XL = 2πfL = 2π × 50 × 0.1 ≈ 31.4 Ω.
Correct answer: 31.4 Ω- A. 15.9 Ω
- B. 31.8 Ω
- C. 47.7 Ω
- D. 63.7 Ω
Explanation: Capacitive reactance Xc = 1/(2πfC) = 1/(2π × 50 × 200 × 10⁻⁶) ≈ 15.9 Ω.
Correct answer: 15.9 Ω- A. 0°
- B. 45°
- C. 90°
- D. 180°
Explanation: In a purely resistive circuit, voltage and current are in phase, so the phase difference is 0°.
Correct answer: 0°- A. Both Xc and XL are doubled
- B. Both Xc and XL are halved
- C. Xc is doubled and XL reduced to half.
- D. XL is doubled and Xc is reduced to half
Explanation: The reactance of a capacitor (Xc) is inversely proportional tofrequency, so it decreases when frequency increases.
Correct answer: XL is doubled and Xc is reduced to half- A. Zero
- B. V × Irms
- C. Vrms / Irms
- D. Vrms2 / R
Explanation: In purely inductive circuit, the phase difference between voltage and current is 90°, so P = VI cosφ = VI cos 90° =0.
Correct answer: Zero- A. 750 W
- B. 1000 W
- C. 1500 W
- D. 2250 W
Explanation: For a resistive circuit, power P = Vrms²/R = 150²/15 = 1500 W.
Correct answer: 1500 W- A. 32.5 Ω
- B. 35.2 Ω
- C. 38.7 Ω
- D. 42.1 Ω
Explanation: Inductive reactance XL = 2πfL = 2π × 50 × 0.04 ≈ 12.56 Ω. Impedance Z = √(R² + XL²) = √(30² + 12.56²) = √(900 + 157.75) ≈ 32.5 Ω.
Correct answer: 32.5 Ω- A. 0.55
- B. 0.65
- C. 0.75
- D. 0.85
Explanation: XL = 2π × 50 × 0.15 ≈ 47.12 Ω, XC = 1/(2π × 50 × 50 × 10⁻⁶) ≈ 63.66 Ω. Net reactance |XL - XC | = 63.66 - 47.12 = 16.54 Ω.
Correct answer: 0.75- A. DC current.
- B. BC current.
- C. AC current.
- D. Magnetic current.
Explanation: AC (Alternating Current) changes its magnitude and direction periodically with time, unlike DC which remains constant.
Correct answer: AC current.- A. 4.5 A
- B. 5.5 A
- C. 6.5 A
- D. 7.5 A
Explanation: X = 2π × 60 × 0.025 ≈ 9.42 Ω. Impedance Z = √(15² + 9.42²) ≈ √(225 + 88.74) ≈ 17.7 Ω.
Correct answer: 5.5 A- A. 30.2 Ω
- B. 35.6 Ω
- C. 40.8 Ω
- D. 45.2 Ω
Explanation: Xc = 1/(2π × 50 × 80 × 10⁻⁶) ≈ 39.79 Ω. Impedance Z = √(25² + 39.79²) = √(625 + 1583.28) ≈ 40.8 Ω.
Correct answer: 45.2 Ω- A. 2 A
- B. 3 A
- C. 4 A
- D. 5 A
Explanation: At resonance, Z = R = 30 Ω. Current I = V/R = 120/30 = 4 A.
Correct answer: 4 A- A. 5.5 A
- B. 6.5 A
- C. 7.5 A
- D. 8.5 A
Explanation: For resistor, IR = 100/15 ≈ 6.67A. For capacitor, Xc = 1/(2π × 60 × 50 × 10⁻⁶) ≈ 53.05 Ω, Ic= 100/53.05 ≈ 1.88 A.
Correct answer: 6.5 A- A. 0.6
- B. 0.7
- C. 0.8
- D. 0.9
Explanation: XL = 2π × 50 × 0.06 ≈ 18.85 Ω. Impedance Z = √(20² + 18.85²) ≈ √(400 + 355.32) ≈ 27.5 Ω.
Correct answer: 0.8- A. 4.8 A
- B. 5.8 A
- C. 6.8 A
- D. 7.8 A
Explanation: XL = 2π × 60 × 0.05 ≈ 18.85 Ω. Impedance Z = √(40² + 18.85²) ≈ √(1600 + 355.32) ≈ 41.2 Ω. Current I = 240/41.2 ≈ 5.83 A, closest to 5.8 A.
Correct answer: 5.8 A- A. 42.4 Ω
- B. 53.1 Ω
- C. 63.7 Ω
- D. 74.3 Ω
Explanation: XC = 1/(2π × 50 × 75 × 10⁻⁶) ≈ 42.44 Ω, closest to 42.4 Ω.
Correct answer: 42.4 Ω- A. 15.2 Ω
- B. 28.9 Ω
- C. 25.8 Ω
- D. 30.2 Ω
Explanation: XL = 2π × 50 × 0.08 ≈ 25.13 Ω, Xc = 1/(2π × 50 × 60 × 10⁻⁶) ≈ 53.05 Ω. Net reactance |XL - Xc | = 53.05 - 25.13 = 27.92 Ω.
Correct answer: 30.2 Ω- A. I0 / √2
- B. I0 / 2
- C. √2 I0
- D. 2 I0
Explanation: The RMS (root-mean-square) current is the effective value of an AC current that delivers the same power as a DC current of the same…
Correct answer: I0 / √2