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Important Questions

Alternating Current — Important Questions

ICSE · Class 12 · Physics

70 important questions from Alternating Current for ICSE Class 12 Physics, with answers. Includes multiple choice and multiple correct questions.

70 questions37 flashcards23 formulas & key relations5 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

Important Questions from Alternating Current

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?
Key topics in Alternating Current include Basic idea of alternating current, Peak value, mean value, and rms value, AC from a rotating coil and AC generator, Reactance and impedance. Study these first, then practise questions on each for the ICSE Class 12 board exam.
How many important questions are there in Alternating Current?
Super Tutor has 70 practice questions for Alternating Current, including multiple choice, multiple correct questions. A sample with answers is on this page.

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Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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All ICSE Class 12 Physics Important Questions

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