Alternating Current Practice Questions

Class 12 · Physics · 2411 free MCQs with instant results and detailed explanations.

2411

Total

826

Easy

1174

Medium

411

Hard

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Topics in Alternating Current

LCR Circuit 620

AC Voltage 506

Transformers 652

Resonance 633

Sample Questions from Alternating Current

Here are 10 sample questions. Start a quiz to get randomized questions with scoring.

Easy

What is the root mean square (RMS) value of an AC voltage given by the equation V(t) = V0 sin(ωt)?

A. V0

B. V0/√2

C. 2V0

D. V0/2

Show Answer & Explanation

Correct Answer: B

The RMS value is calculated as V0/√2 for a sine wave.

Easy

In a pure inductive circuit connected to an AC source, what is the phase difference between voltage and current?

A. 0°

B. 90°

C. 180°

D. 45°

Show Answer & Explanation

Correct Answer: B

In a pure inductive circuit, the current lags the voltage by 90 degrees.

Easy

What is the average power consumed in an AC circuit with a resistance R when the RMS voltage is V_rms?

A. V_rms^2 / R

B. V_rms * R

C. R / V_rms

D. V_rms^2 * R

Show Answer & Explanation

Correct Answer: A

The average power is given by P = V_rms^2 / R in a resistive circuit.

Medium

What is the average value of a full-wave rectified AC voltage with a peak value of 5 V?

A. 1.57 V

B. 2.5 V

C. 3.18 V

D. 4 V

Show Answer & Explanation

Correct Answer: A

The average value of a full-wave rectified voltage is given by V_avg = (2 * V_m) / π. Here, V_avg = (2 * 5) / π ≈ 1.57 V.

Medium

In an AC circuit, if the frequency is doubled, how does the inductive reactance change?

A. It remains the same

B. It doubles

C. It halves

D. It quadruples

Show Answer & Explanation

Correct Answer: C

Inductive reactance (X_L) is given by X_L = 2πfL. If the frequency (f) is doubled, X_L will also double, showing that it increases linearly.

Medium

If a resistor of 20 ohms is connected to an AC source, what will be the power dissipation if the RMS voltage across it is 100 V?

A. 250 W

B. 500 W

C. 1000 W

D. 2000 W

Show Answer & Explanation

Correct Answer: B

Power in a resistive load is given by P = V_rms²/R. Here, P = (100 V)² / 20 Ω = 500 W.

Medium

What is the phase difference between voltage and current in a purely resistive AC circuit?

A. 90 degrees

B. 0 degrees

C. 180 degrees

D. 45 degrees

Show Answer & Explanation

Correct Answer: B

In a purely resistive circuit, the current and voltage are in phase, meaning the phase difference is 0 degrees.

Hard

In an AC circuit, the voltage is given by V(t) = V0 sin(ωt + φ). What does φ represent in this equation?

A. Amplitude of the voltage

B. Phase constant

C. Frequency of the voltage

D. Time period

Show Answer & Explanation

Correct Answer: B

φ represents the phase constant, which indicates the initial angle at time t=0.

Hard

In a series RLC circuit, if the resistance is 10 Ω, inductance is 0.5 H, and capacitance is 100 μF, what is the resonant frequency?

A. 10 Hz

B. 20 Hz

C. 30 Hz

D. 50 Hz

Show Answer & Explanation

Correct Answer: A

The resonant frequency fr = 1/(2π√(LC)), substituting L and C gives fr ≈ 10 Hz.

Q10

Hard

Which of the following statements about AC circuits is incorrect?

A. AC voltage can be transformed using transformers.

B. AC current can be stored in batteries.

C. AC circuits can have reactive components.

D. AC power can be calculated using P = VI cos(φ).

Show Answer & Explanation

Correct Answer: B

AC current cannot be stored in batteries, which convert it to DC.

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Alternating Current — Class 12 Physics Practice Questions Online

This page contains 2411 practice MCQs for the chapter Alternating Current in Class 12 Physics. The questions are organized by difficulty — 826 easy, 1174 medium, 411 hard — so you can choose the right level for your preparation.

Every question includes a detailed explanation to help you understand the concept, not just memorize answers. Take a timed quiz to simulate exam conditions, or practice at your own pace with no time limit. This chapter covers 4 topics, giving you comprehensive coverage of the entire chapter.