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Alternating current
5 Class 12 Physics questions with answers and explanations.
Printable worksheet with answer key
All questions with answers
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The rms value of an AC with peak value 10 A is:
- 1 14.1 A
- 2 7.07 A
- 3 10 A
- 4 5 A
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Correct answer: 7.07 A
I rms = I0 / square root of 2 = 7.07 A.
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In a purely resistive AC circuit, the current and voltage are:
- 1 180 degrees apart
- 2 90 degrees apart
- 3 Unrelated
- 4 In phase
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Correct answer: In phase
For a resistor the current is in phase with the voltage.
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Capacitive reactance is given by:
- 1 2 pi f L
- 2 2 pi f C
- 3 1 / (2 pi f L)
- 4 1 / (2 pi f C)
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Correct answer: 1 / (2 pi f C)
X_C = 1 / (omega C) = 1 / (2 pi f C).
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Inductive reactance:
- 1 Increases with frequency
- 2 Decreases with frequency
- 3 Is zero always
- 4 Does not change
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Correct answer: Increases with frequency
X_L = 2 pi f L, so it rises with frequency.
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At resonance in a series LCR circuit, the impedance is:
- 1 Infinite
- 2 Minimum and equal to R
- 3 Maximum
- 4 Zero
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Correct answer: Minimum and equal to R
X_L = X_C cancel, so impedance equals R.
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