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JEE • PHYSICS • ALTERNATING CURRENT

Alternating current practice · Hard

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Practice format and chapter quiz

These sets use single-correct-answer MCQs. They do not cover every JEE Main or JEE Advanced question format and are not full-length mock papers.

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1 Hard

1 of 8

Application +4 | -1

A resistance of 20 ohms is connected to a source of an alternating potential

V = 220\sin \left[ {100\,\pi \,t} \right]

. The time taken by the current to change from its peak value to r.m.s. value is [in sec]

View answer and explanation

Correct option: D

2.5 \times {10^{ - 3}}

Option D (

2.5 \times {10^{ - 3}}

) is correct because it is the time calculated for the current to change from its peak value to its RMS value.

2 Hard

2 of 8

Application +4 | -1

AC voltage V(t)

= \mathrm{20 sin}\,\mathrm{\omega t}

of frequency 50 Hz is applied to a parallel plate capacitor. The separation between the plates is 2 mm and the area is

1\,{m^2}.

The amplitude of the oscillating displacement current for the applied AC voltage is ….
[Take,

{\varepsilon _0} = 8.85 \times {10^{ - 12}}F/m]

View answer and explanation

Correct option: C

\mathrm{27}\mathrm{.79 \mu A}

Option C (

\mathrm{27}\mathrm{.79 \mu A}

) is correct because it is the calculated amplitude of the oscillating displacement current using the given AC voltage, frequency, plate separation, and area.

3 Hard

3 of 8

Application +4 | -1

A voltage of peak value 283 V and varying frequency is applied to a series L – C – R combination in which

R = 3\;\mathrm{\Omega }

L = 25

mH and

C = 400\mu \mathrm{F}

. The frequency (in Hz)of the source at which maximum power is dissipated in the above, is

View answer and explanation

Correct option: D

50.3

Option D (50.3) is correct because maximum power dissipation occurs at resonance, and the resonant frequency is calculated using the formula v = 1/(2*pi*sqrt(LC)).

4 Hard

4 of 8

Application +4 | -1

The peak voltage of 220 volt AC mains (in volt) is

View answer and explanation

Correct option: C

311

Option C (311) is correct because the peak voltage is calculated by multiplying the RMS voltage by the square root of 2.

5 Hard

5 of 8

Application +4 | -1

What is the value of inductance L for which the current is a maximum in a series L-C-R circuit with

C = 10\mu \mathrm{F}

and

\omega = 1000\;{\mathrm{s}^{ - 1}}?

View answer and explanation

Correct option: A

100 mH

Option A (100 mH) is correct because the current is maximum at resonance, where the inductive reactance equals the capacitive reactance, leading to L = 1/(

\omega^2

C).

6 Hard

6 of 8

Understanding +4 | -1

For a series R-L-C circuit:

(a) Voltage across L and C differ by

\pi

phase

(b) Current through L and R are in same phase

(c) Voltage across R and L differ by

\pi/2

phase

(d) Voltage across L and current through C differ by

\pi/2

phase

View answer and explanation

Correct option: D

All are correct

Option D (All are correct) is correct because it accurately describes the phase relationships between voltage and current in a series RLC circuit.

7 Hard

7 of 8

Application +4 | -1

In an AC circuit, V and I are given by V = 100 sin [100 t] volts, I = 100 sin

\left[ {100\,t + \frac{\pi }{3}} \right]

mA. The power dissipated in casuist is [in watt]

View answer and explanation

Correct option: C

2.5

Option C (2.5) is correct because the power dissipated is calculated using the RMS values of voltage and current, along with the phase difference between them.

8 Hard

8 of 8

Analyzing +4 | -1

An ac source of angular frequency ω is fed across a resistor r and a capctior C in series. The current registered is

I

. If the frequency of source is changed to ω/3 (maintaining the same voltage), the current in the circuit is found to be halved. Calculate the ratio of reactance to resistance at the original frequency ω

View answer and explanation

Correct option: A

\sqrt {\frac{3}{5}}

The ratio of reactance to resistance at the original frequency is

\sqrt{\frac{3}{5}}

(Option A) because it is derived from the given current and frequency changes in the RC circuit.

Revision notes and key takeaways

Review ALTERNATING CURRENT in your textbook or class notes, then use this set to check your understanding.

Key Takeaways

✓ This set contains 8 single-correct-answer MCQs on ALTERNATING CURRENT.
✓ Try each question before opening its answer. Read the explanation where one is available.
✓ Sign in to save submitted answers. Revisit incorrect answers alongside your textbook or class notes.

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