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JEE • PHYSICS • ALTERNATING CURRENT

Alternating current practice · Easy

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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 Easy

1 of 25

Analyzing +4 | -1

In series

L C R

circuit voltage drop across resistance is

8 {~V}

, across inductor is

6 {~V}

and across capacitor is

12 {~V}

. Then

View answer and explanation

Correct option: D

None of these

Option D (None of these) is correct because the current leads the voltage, the source voltage is less than the voltage across the capacitor, and the power factor is 4/5, not 4/3.

2 Easy

2 of 25

Understanding +4 | -1

The current in series LCR circuit will be maximum when ω is

View answer and explanation

Correct option: D

\sqrt {1/LC}

Option D (

\sqrt {1/LC}

) is correct because the current in a series LCR circuit is maximum at resonance, which occurs when

\omega = \sqrt{\frac{1}{LC}}

3 Easy

3 of 25

Application +4 | -1

A step-up transformer is used on a 120 V line to provide a potential difference of 2400 V. If the primary coil has 75 turns, the number of turns in the secondary coil is

View answer and explanation

Correct option: C

1500

Option C (1500) is correct because the ratio of turns in the secondary and primary coils is equal to the ratio of the voltages.

4 Easy

4 of 25

Remembering +4 | -1

The power factor of LCR circuit at resonance is

View answer and explanation

Correct option: B

Option B (1) is correct because at resonance, the LCR circuit behaves as a purely resistive circuit, and the power factor for a purely resistive circuit is 1.

5 Easy

5 of 25

Remembering +4 | -1

Hot wire ammeters can be used for measuring:

View answer and explanation

Correct option: A

Both AC and DC

Option A (Both AC and DC) is correct because hot wire ammeters measure the heating effect of current, which is independent of the current's direction.

6 Easy

6 of 25

Remembering +4 | -1

The power factor of LCR circuit at resonance is

View answer and explanation

Correct option: B

Option B (1) is correct because at resonance, the impedance of an LCR circuit is purely resistive, resulting in a power factor of 1.

7 Easy

7 of 25

Understanding +4 | -1

At high frequency, the capacitor offer

View answer and explanation

Correct option: B

Less reactance

Option B (Less reactance) is correct because capacitive reactance is inversely proportional to frequency, so at high frequency, the capacitor offers less reactance.

8 Easy

8 of 25

Application +4 | -1

Write the equation of a sinusoidal voltage of rms valus

220 \mathrm{~V}

and frequency

50 \mathrm{~Hz}

View answer and explanation

Correct option: B

220 \sqrt{2} \sin (100 \pi t)

Option B (

220 \sqrt{2} \sin (100 \pi t)

) is correct because it represents a sinusoidal voltage with the correct RMS value and frequency.

9 Easy

9 of 25

Understanding +4 | -1

A LCR circuit is at resonance for a capacitor C, inductance

\mathrm{L}

and resistance

\mathrm{R}

. Now the value of resistance is halved keeping all other parameters same. The current amplitude at resonance will be now:

View answer and explanation

Correct option: B

double

Option B (double) is correct because at resonance, the impedance is equal to the resistance, so halving the resistance doubles the current amplitude.

10 Easy

10 of 25

Understanding +4 | -1

The core of a transformer is laminated to reduce energy losses due to

View answer and explanation

Correct option: A

Eddy currents

Option A (Eddy currents) is correct because laminating the core increases resistance, reducing the magnitude of eddy currents and thus energy losses.

11 Easy

11 of 25

Application +4 | -1

Statement I: In a series

R-L-C

circuit the voltage across-resistor, inductor and capacitor are

8 \mathrm{~V}, 16 \mathrm{~V}

and

10 \mathrm{~V}

respectively. The resultant emf in the circuit is

10 \mathrm{~V}

.

Statement II: Resultant emf of the circuit is given by the relation

E=\sqrt{V_R^2+\left(V_L-V_C\right)^2}

View answer and explanation

Correct option: A

Statement I is true, Statement II is true; Statement II is
the correct explanation for Statement I

Statement I is true, and Statement II is also true and the correct explanation for Statement I because the resultant EMF is calculated using the given formula and matches the statement.

12 Easy

12 of 25

Application +4 | -1

A step-up transformer is used on a 120 V line to provide a potential difference of 2400 V. If the primary coil has 75 turns, the number of turns in the secondary coil is

View answer and explanation

Correct option: C

1500

Option C (1500) is correct because the ratio of turns in the secondary to primary coil is equal to the ratio of voltages.

13 Easy

13 of 25

Understanding +4 | -1

In an ideal choke, ratio of its inductance L to its DC resistance R is

View answer and explanation

Correct option: A

Infinity

Option A (Infinity) is correct because an ideal choke has zero DC resistance, making the ratio of inductance to resistance infinite.

14 Easy

14 of 25

Understanding +4 | -1

Statement I: The power factor of an inductor is zero.

Statement II: In the inductor, the emf and current differ in phase by

\frac{\pi}{2}

View answer and explanation

Correct option: A

Statement I is true, Statement II is true; Statement II is
the correct explanation for Statement I

Option A (Statement I is true, Statement II is true; Statement II is the correct explanation for Statement I) is correct because the power factor is the cosine of the phase angle between voltage and current, and in an inductor, the phase difference is

\frac{\pi}{2}

, making the power factor zero.

15 Easy

15 of 25

Application +4 | -1

In an AC circuit, the instantaneous values of emf and current are e=200sin⁡314t volt and

I = \sin \left( {314t + \frac{\pi }{3}} \right)\,amp

, The average power consumed in watt is

View answer and explanation

Correct option: C

Option C (50) is correct because the average power consumed is calculated using P = Vrms * Irms * cos(phi).

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16 Easy

16 of 25

Understanding +4 | -1

The instantaneous values of current and emf in an ac circuit are

I = 1/\sqrt 2

\sin 314\;t\;amp

and

E = \sqrt 2 \sin \left( {314\;t - \pi /6} \right)V

respectively. The phase difference between E and I will be

View answer and explanation

Correct option: A

- \pi /6\;rad

Option A (

- \pi /6\;rad

) is correct because the phase difference is the difference between the phase angles of the voltage and current.

17 Easy

17 of 25

Understanding +4 | -1

In an AC series circuit, the instantaneous current is maximum when the instantaneous voltage is maximum. The circuit element connected to the source will be

View answer and explanation

Correct option: C

Pure resistor

Option C (Pure resistor) is correct because in a purely resistive AC circuit, the voltage and current are in phase, meaning they reach their maximum values simultaneously.

18 Easy

18 of 25

Understanding +4 | -1

An alternating e.m.f. is applied to purely capacitive circuit. The phase relation between e.m.f. and current flowing in the circuit is or
In a circuit containing capacitance only

View answer and explanation

Correct option: B

Current is ahead of e.m.f. by

\pi /2

Option B (Current is ahead of e.m.f. by

\pi /2

) is correct because in a purely capacitive circuit, the current leads the voltage by 90 degrees.

19 Easy

19 of 25

Understanding +4 | -1

In an ac circuit, the instantaneous current is zero, when the instantaneous voltage is maximum. In this case, the source may be connected to:
A. pure inductor.
B. pure capacitor.
C. pure resistor.
D. combination of an inductor and capacitor.
Choose the correct answer from the options given below:

View answer and explanation

Correct option: D

A, B and D only

Option D (A, B and D only) is correct because in a pure inductor, pure capacitor, or a combination of inductor and capacitor, the instantaneous current can be zero when the instantaneous voltage is maximum due to a phase difference of

\frac{\pi}{2}

20 Easy

20 of 25

Application +4 | -1

The ratio of turns in primary and secondary coils of a transformer is 1 : 20. The ratio of currents in primary and secondary coils will be

View answer and explanation

Correct option: B

0.834027778

Option B (20:01) is correct because the ratio of currents in the primary and secondary coils is inversely proportional to the ratio of turns.

21 Easy

21 of 25

Understanding +4 | -1

A bulb is connected first with dc and then ac of same voltage it will shine brightly with

View answer and explanation

Correct option: D

Equally with both

Option D (Equally with both) is correct because the power consumed by the bulb depends on its resistance, which is the same for both AC and DC.

22 Easy

22 of 25

Application +4 | -1

A generator produces a voltage that is given by

V = 240\sin 120\;t

, where t is in seconds. The frequency and r.m.s. voltage are

View answer and explanation

Correct option: C

19 Hz and 170 V

Option C (19 Hz and 170 V) is correct because the frequency is calculated from the angular frequency and the r.m.s voltage is the peak voltage divided by the square root of 2.

23 Easy

23 of 25

Remembering +4 | -1

In L – C – R series circuit the resonance condition in terms of capacitive reactance

\left( {{X_C}} \right)

and inductive reactance

\left( {{X_L}} \right)

View answer and explanation

Correct option: D

{X_C} - {X_L} = 0

Option D (

{X_C} - {X_L} = 0

) is correct because at resonance in an LCR series circuit, the capacitive reactance equals the inductive reactance, making their difference zero.

24 Easy

24 of 25

Understanding +4 | -1

In an ac circuit with voltage V and current I, the power dissipated is

View answer and explanation

Correct option: D

Depends on the phases between V and I

Option D (Depends on the phases between V and I) is correct because the power dissipated in an AC circuit depends on the phase angle between voltage and current, as given by

P = VI\cos\phi

25 Easy

25 of 25

Remembering +4 | -1

Transformer works on the principle of

View answer and explanation

Correct option: A

Mutual induction between two coils

Option A (Mutual induction between two coils) is correct because a transformer operates based on the principle of mutual induction, where a changing magnetic field in one coil induces a voltage in another coil.

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 25 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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