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Important Questions

Alternating Current

ICSE · Class 12 · Physics

Most important questions from Alternating Current for ICSE Class 12 Physics board exam 2026. MCQs, short answer, and long answer questions with marks.

70 questions37 flashcards5 concepts

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A graph showing the linear relationship between inductive reactance (X_L) and frequency (f or ω), demonstrating that X_L increases proportionally with frequency.
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70 Questions·
multiple choicemultiple correct

Sample Questions

1multiple choice
3 marks

A 200 V sinusoidal voltage is applied to a series L-R circuit with resistance 10 ohm and inductance 0.8 H. The angular frequency is 300 rad/s. What is the peak current in the circuit?

Show answer

0.83 A

First find XL = omega L = 300 x 0.8 = 240 ohm. Then Z = sqrt(10^2 + 240^2) = 240.2 ohm approximately. The peak voltage is V0 = 200 V. So I0 = V0/Z = 200/240.2 = 0.83 A.

2multiple choice
3 marks

A 100 microfarad capacitor is in series with a 40 ohm resistor and connected to a 110 V, 60 Hz supply. What is the maximum current in the circuit?

Show answer

3.23 A

Find XC = 1/(2 pi f C) = 1/(2 x 3.14 x 60 x 100 x 10^-6) = 26.5 ohm. Then Z = sqrt(40^2 + 26.5^2) = 48 ohm approximately. Peak voltage is V0 = 110 x 1.414 = 155.5 V. So I0 = V0/Z = 155.5/48 = 3.23 A.

3multiple choice
3 marks

A 230 V, 50 Hz source is connected to a series circuit containing a 80 mH inductor and a 60 microfarad capacitor with negligible resistance. What is the current amplitude in the circuit?

Show answer

11.6 A

For a pure L-C circuit, Z = |XC - XL|. Here XL = 2 pi f L = 2 x 3.14 x 50 x 0.08 = 25.1 ohm. XC = 1/(2 pi f C) = 1/(2 x 3.14 x 50 x 60 x 10^-6) = 53.1 ohm. So Z = 53.1 - 25.1 = 28.0 ohm. Peak voltage V0 = 230 x 1.414 = 325.2 V. Therefore I0 = V0/Z = 325.2/28.0 = 11.6 A.

4multiple choice
3 marks

In a series L-C-R circuit, R = 100 ohm, L = 0.12 H, C = 480 nF, and the rms supply voltage is 230 V. What is the resonant frequency?

Show answer

663 Hz

Resonant frequency is f0 = (1/2 pi) sqrt(1/LC). Substituting L = 0.12 H and C = 480 x 10^-9 F gives f0 = (1/2 x 3.14) x sqrt(1/(0.12 x 480 x 10^-9)). This evaluates to about 663 Hz.

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Frequently Asked Questions

What are the important topics in Alternating Current for ICSE Class 12 Physics?
Alternating Current covers several key topics that are frequently asked in ICSE Class 12 board exams. Focus on the core concepts listed on this page and practise related questions to build confidence.
How to score full marks in Alternating Current — ICSE Class 12 Physics?
Understand the core concepts first, then work through the 70 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.
How many important questions are there in Alternating Current?
There are 70 practice questions available for Alternating Current. These cover multiple question types including MCQs, short answer, and long answer questions.

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