A small signal voltage ${\rm{V(t)}}\,{\rm{ = }}\,{{\rm{V}}_{\rm{0}}}{\rm{sin}}\,{\rm{\omega t}}$ is applied across an ideal capacitor C:

Current I (t), legs voltage V (t) by ${90^{\rm{o}}}$

Current I (t) is in phase with voltage V (t).

Current I (t) leads voltage V (t) by ${180^{\rm{o}}}$

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JEE • PHYSICS • ALTERNATING CURRENT

Alternating current practice · Medium

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Showing 241-246 of 246 questions

241 Medium

241 of 246

Application +4 | -1

An inductor of inductance

100 \mathrm{~mH}

is connected in series with a resistance, a variable capacitance and an AC source of frequency

2.0 \mathrm{~kHz}

. What should be the value of the capacitance so that maximum current may be drawn into the circuit?

View answer and explanation

Correct option: A

63 \mathrm{~nF}

Option A (63 nF) is correct because maximum current is drawn at resonance, where the capacitive reactance equals the inductive reactance, leading to

C = \frac{1}{\omega^2 L}

242 Medium

242 of 246

Understanding +4 | -1

Assertion: The average value of alternating emf is

63.39 \%

of the peak value.

Reason:The rms value of alternating emf is

70.72 \%

of peak value.

View answer and explanation

Correct option: B

If both assertion and reason are true and reason is not correct explanation of assertion.

Option B (If both assertion and reason are true and reason is not correct explanation of assertion) is correct because both the average and RMS values are related to the peak value, but the RMS value doesn't directly explain the average value.

243 Medium

243 of 246

Understanding +4 | -1

Mark the correct statement.

View answer and explanation

Correct option: A

Ideal inductor does not dissipate power in an AC circuit

Option A (Ideal inductor does not dissipate power in an AC circuit) is correct because the average power dissipated by an ideal inductor over a complete cycle is zero.

244 Medium

244 of 246

Understanding +4 | -1

A small signal voltage

\mathrm{V(t)}\,\mathrm{ = }\,{\mathrm{V}_\mathrm{0}}\mathrm{sin}\,\mathrm{\omega t}

is applied across an ideal capacitor C:

View answer and explanation

Correct option: B

Over a full cycle the capacitor C does not consume any energy from the voltage source

Option B (Over a full cycle the capacitor C does not consume any energy from the voltage source) is correct because the energy stored in a capacitor during charging is released during discharging, resulting in zero net energy consumption over a cycle.

245 Medium

245 of 246

Analyzing +4 | -1

Assertion: A bulb connected in series with a solenoid is connected to ac source. If a soft iron core is introduced in the solenoid, the bulb will glow brighter.

Reason: On introducing soft iron core in the solenoid, the inductance increases.

View answer and explanation

Correct option: D

If assertion is false but reason is true.

Option D is correct because the assertion is false (bulb glows dimmer), but the reason is true (inductance increases).

246 Medium

246 of 246

Understanding +4 | -1

Statement (A): When frequency is greater than resonance frequency in a series LCR circuit, it will be an inductive circuit.

Statement (B): Resultant voltage will lead the current in LR circuit.

View answer and explanation

Correct option: A

Both (A) and (B) are true

Option A is correct because in a series LCR circuit, when the frequency is greater than the resonance frequency, the circuit behaves inductively, and in an LR circuit, the voltage leads the current.

Revision notes and key takeaways

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