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Alternating Current Practice Questions

JEE · Physics · 1631 free MCQs with instant results and detailed explanations.

1631
Total
394
Easy
729
Medium
508
Hard

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Topics in Alternating Current

Resonance 299
Transformers 300
LCR Circuit 266
AC Voltage 254
Phasor Diagrams 288
Power in AC Circuits 224

Sample Questions from Alternating Current

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

Q1
Easy
What is the root mean square (RMS) voltage of an AC supply if its peak voltage is 100 V?
A. 70.7 V
B. 100 V
C. 141.4 V
D. 50 V
Show Answer & Explanation
Correct Answer: A
RMS voltage is calculated as peak voltage divided by √2. Thus, 100 V / √2 = 70.7 V.
Q2
Easy
In an AC circuit, if the frequency is doubled, what happens to the reactance of an inductor?
A. Doubles
B. Halves
C. Quadruples
D. Remains the same
Show Answer & Explanation
Correct Answer: B
Inductive reactance (XL = 2πfL) is inversely proportional to frequency. If frequency doubles, reactance halves.
Q3
Easy
What is the phase difference between the voltage and the current in a purely resistive AC circuit?
A. 0 degrees
B. 90 degrees
C. 180 degrees
D. 45 degrees
Show Answer & Explanation
Correct Answer: A
In a purely resistive circuit, voltage and current are in phase, hence the phase difference is 0 degrees.
Q4
Medium
An AC circuit has a peak voltage of 100 V. What is the RMS voltage?
A. 70.71 V
B. 100 V
C. 141.42 V
D. 50 V
Show Answer & Explanation
Correct Answer: A
The RMS voltage is calculated by dividing the peak voltage by √2, which gives approximately 70.71 V.
Q5
Medium
In a pure resistive AC circuit, what is the phase difference between voltage and current?
A. 0 degrees
B. 90 degrees
C. 180 degrees
D. 45 degrees
Show Answer & Explanation
Correct Answer: A
In a purely resistive circuit, voltage and current are in phase, meaning their phase difference is 0 degrees.
Q6
Medium
An AC voltage source has an output of V(t) = 12 cos(100t + π/3). What is the peak voltage?
A. 12 V
B. 6 V
C. 24 V
D. 10 V
Show Answer & Explanation
Correct Answer: A
The peak voltage is given by the coefficient of the cosine function. Here, it is 12 V.
Q7
Medium
In a capacitor connected to an AC source, how does the current relate to the voltage?
A. Current lags voltage by 90 degrees
B. Current leads voltage by 90 degrees
C. Current is in phase with voltage
D. Current leads voltage by 45 degrees
Show Answer & Explanation
Correct Answer: B
In a purely capacitive AC circuit, the current leads the voltage by 90 degrees.
Q8
Hard
An AC voltage source provides a voltage described by V(t) = V0 sin(ωt). If V0 = 100 V and ω = 100 rad/s, what is the peak current if the load resistance R = 50 Ω?
A. 2 A
B. 1 A
C. 4 A
D. 0.5 A
Show Answer & Explanation
Correct Answer: A
The peak current can be calculated using Ohm's law, where I0 = V0/R. Substituting the given values gives I0 = 100 V / 50 Ω = 2 A.
Q9
Hard
What is the phase difference between the voltage and current in an ideal inductive circuit when connected to an AC source?
A. 0°
B. 90°
C. 180°
D. 60°
Show Answer & Explanation
Correct Answer: B
In an ideal inductive circuit, the voltage leads the current by 90 degrees due to the properties of inductance.
Q10
Hard
In a series RLC circuit, the impedance Z is given by Z = √(R^2 + (XL - XC)^2). If R = 10 Ω, XL = 30 Ω, and XC = 20 Ω, what is the impedance?
A. 10 Ω
B. 20 Ω
C. 35 Ω
D. 40 Ω
Show Answer & Explanation
Correct Answer: C
Substituting R, XL, and XC into the formula gives Z = √(10² + (30 - 20)²) = √(100 + 10) = √110 ≈ 10.49 Ω.

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Alternating Current — JEE Physics Practice Questions Online

This page contains 1631 practice MCQs for the chapter Alternating Current in JEE Physics. The questions are organized by difficulty — 394 easy, 729 medium, 508 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 6 topics, giving you comprehensive coverage of the entire chapter.