Quiz Tweek

Preparing your workspace...

Alternating Current Set-5 MCQ Online Practice Test | Class 12 | Quiz Tweek

Alternating Current Set-5

Practice Important MCQs for Alternating Current — Physics, Class 12.

Alternating Current (AC) is central to understanding how electricity is generated, transmitted, and utilized in real engineering systems. In CBSE and competitive exams like JEE/NEET, AC problems test core ideas such as impedance, power factor, resonance in RLC circuits, reactive power, and power delivery—concepts that frequently appear in both numericals and conceptual questions.

Minutes

Questions

1 / -0

Marking

Question Bank Preview

Q1. A sinusoidal voltage $v(t)=120\sqrt{2}\sin(100\pi t)\ \mathrm{V}$ is applied across a resistor $R=40\ \Omega$ . What is the average power dissipated in the resistor?

(A)

$180\ \mathrm{W}$

(B)

$1440\ \mathrm{W}$

(C)

$360\ \mathrm{W}$

(D)

$720\ \mathrm{W}$

Q2. A series RLC circuit has $R=20\ \Omega$ , $L=0.1\ \mathrm{H}$ and $C=100\ \mu\mathrm{F}$ . It is connected to a sinusoidal source of amplitude $100\ \mathrm{V}$ at frequency $50\ \mathrm{Hz}$ . What is the amplitude of the steady‑state current in the circuit?

(A)

$5.00\ \mathrm{A}$

(B)

$4.00\ \mathrm{A}$

(C)

$10.00\ \mathrm{A}$

(D)

$1.00\ \mathrm{A}$

Q3. A series circuit consists of a resistor $R=100\ \Omega$ and an inductor $L=50\ \mathrm{mH}$ connected to an AC source of $100\ \mathrm{V}$ (rms) at frequency $1\ \mathrm{kHz}$ . What are the power factor of the circuit and the average power consumed?

(A)

$\text{pf}=0.95,\ P\approx 90\ \mathrm{W}$

(B)

$\text{pf}=0.60,\ P\approx 36\ \mathrm{W}$

(C)

$\text{pf}=0.80,\ P\approx 64\ \mathrm{W}$

(D)

$\text{pf}\approx 0.303,\ P\approx 9.22\ \mathrm{W}$

Q4. A series RLC circuit has $R=2\ \Omega$ , $L=0.2\ \mathrm{H}$ and $C=50\ \mu\mathrm{F}$ . It is connected to an AC source of $100\ \mathrm{V}$ (rms) and the frequency is adjusted to resonance. Calculate the quality factor $Q$ of the circuit and the RMS voltage across the inductor at resonance.

(A)

$Q\approx 31.6,\ V_{L,\text{rms}}\approx 4.47\ \mathrm{kV}$

(B)

$Q\approx 31.62,\ V_{L,\text{rms}}\approx 3.162\ \mathrm{kV}$

(C)

$Q\approx 0.0316,\ V_{L,\text{rms}}\approx 3.162\ \mathrm{kV}$

(D)

$Q\approx 63.2,\ V_{L,\text{rms}}\approx 1.58\ \mathrm{kV}$

Q5. A single‑phase inductive load consumes $P=4.0\ \mathrm{kW}$ at power factor $0.80$ (lagging) from a $230\ \mathrm{V}$ , $50\ \mathrm{Hz}$ supply. A capacitor is to be connected in parallel with the load to improve the power factor to $0.95$ (lagging). What capacitance $C$ is required? (Take $\omega=2\pi\times 50\ \mathrm{rad/s}$ .)

(A)

$C\approx 102\ \mu\mathrm{F}$

(B)

$C\approx 180\ \mu\mathrm{F}$

(C)

$C\approx 67\ \mu\mathrm{F}$

(D)

$C\approx 204\ \mu\mathrm{F}$

Q6. A sinusoidal voltage $v(t)=170\sin(100\pi t)\ \mathrm{V}$ is applied across a resistor $R=100\ \Omega$ . The resistor is connected to the source for $10\ \mathrm{s}$ . The energy dissipated in the resistor during this time is approximately:

(A)

$1.20\times10^{3}\ \mathrm{J}$

(B)

$1.445\times10^{3}\ \mathrm{J}$

(C)

$8.48\times10^{2}\ \mathrm{J}$

(D)

$2.89\times10^{3}\ \mathrm{J}$

Q7. A series circuit contains $R=5\ \Omega$ , $L=0.20\ \mathrm{H}$ and $C=50\ \mu\mathrm{F}$ connected to an AC source of rms voltage $230\ \mathrm{V}$ at frequency $50\ \mathrm{Hz}$ . The rms voltage across the capacitor is nearest to:

(A)

$2.89\times10^{3}\ \mathrm{V}$

(B)

$230\ \mathrm{V}$

(C)

$1.15\times10^{4}\ \mathrm{V}$

(D)

$1.15\times10^{3}\ \mathrm{V}$

Q8. A single-phase inductive load absorbs $P=10\ \mathrm{kW}$ from a $230\ \mathrm{V}$ , $50\ \mathrm{Hz}$ supply at power factor $0.60$ (lagging). A capacitor is connected in parallel to improve the power factor to unity. The capacitance required is closest to:

(A)

$160\ \mu\mathrm{F}$

(B)

$400\ \mu\mathrm{F}$

(C)

$802\ \mu\mathrm{F}$

(D)

$8.02\ \mu\mathrm{F}$

Q9. For a series $R\!-\!L\!-\!C$ circuit with $R=10\ \Omega$ , $L=0.10\ \mathrm{H}$ and $C=100\ \mu\mathrm{F}$ connected to an AC source, the frequency $f$ (in Hz) at which the circuit current leads the applied voltage by $45^\circ$ is closest to:

(A)

$27\ \mathrm{Hz}$

(B)

$50\ \mathrm{Hz}$

(C)

$60\ \mathrm{Hz}$

(D)

$43\ \mathrm{Hz}$

Q10. A balanced star-connected three-phase inductive load draws $P=30\ \mathrm{kW}$ at line voltage $415\ \mathrm{V}$ and $50\ \mathrm{Hz}$ with power factor $0.80$ (lagging). Capacitors are connected in delta across the line to correct the power factor to unity. The capacitance required per capacitor (approximately) is:

(A)

$69\ \mu\mathrm{F}$

(B)

$139\ \mu\mathrm{F}$

(C)

$278\ \mu\mathrm{F}$

(D)

$46\ \mu\mathrm{F}$

Q11. A series RLC circuit has $R=10\,\Omega$ , $L=0.20\,\mathrm{H}$ and $C=100\,\mu\mathrm{F}$ . It is connected to an AC source of RMS voltage $V_{\rm rms}=100\ \mathrm{V}$ at frequency $f=50\ \mathrm{Hz}$ . The RMS current $I_{\rm rms}$ in the circuit is approximately:

(A)

$3.14\ \mathrm{A}$

(B)

$1.59\ \mathrm{A}$

(C)

$3.07\ \mathrm{A}$

(D)

$10.0\ \mathrm{A}$

Q12. An industrial load consumes $P=50\ \mathrm{kW}$ at a lagging power factor $\cos\phi=0.60$ from an AC supply of RMS voltage $V=230\ \mathrm{V}$ and frequency $f=50\ \mathrm{Hz}$ . A capacitor is connected in parallel to correct the power factor to unity. The required capacitance $C$ is approximately:

(A)

$40.0\,\mu\mathrm{F}$

(B)

$4.00\times10^{-3}\ \mathrm{F}$

(C)

$400\ \mu\mathrm{F}$

(D)

$4.00\,\mu\mathrm{F}$

Q13. In a series RLC circuit $R=20\,\Omega$ , $L=0.20\,\mathrm{H}$ and $C=50.0\,\mu\mathrm{F}$ . Using $f_0=\dfrac{1}{2\pi\sqrt{LC}}$ , $Q=\dfrac{\omega_0L}{R}$ and bandwidth $\Delta f=\dfrac{f_0}{Q}$ , the bandwidth $\Delta f$ (difference between the two half-power frequencies) around resonance is approximately:

(A)

$15.9\ \mathrm{Hz}$

(B)

$31.7\ \mathrm{Hz}$

(C)

$3.16\ \mathrm{Hz}$

(D)

$50.3\ \mathrm{Hz}$

Q14. A series RLC circuit has $R=5.0\,\Omega$ and $L=0.10\,\mathrm{H}$ . The capacitor is chosen so that the circuit is in resonance at $f=50.0\ \mathrm{Hz}$ . If the circuit is connected to an AC source of RMS voltage $100\ \mathrm{V}$ , the RMS voltage across the inductor at resonance is approximately:

(A)

$100\ \mathrm{V}$

(B)

$6.28\times10^{3}\ \mathrm{V}$

(C)

$62.8\ \mathrm{V}$

(D)

$6.28\times10^{2}\ \mathrm{V}$

Q15. Assertion: The average power absorbed by an ideal inductor over one period of any periodic current is zero. Reason: The average voltage across an ideal inductor over one period is zero because $v=L\,\dfrac{di}{dt}$ and $\displaystyle\int_0^T\frac{di}{dt}\,dt=0$ . Which of the following is correct?

(A)

Both assertion and reason are true and reason explains the assertion.

(B)

Both assertion and reason are true but reason does not explain the assertion.

(C)

Assertion is true but reason is false.

(D)

Assertion is false but reason is true.

More Quizzes for Class 12

Explore other chapters and subjects, or view all quizzes for this class.

Quiz Tweek

Alternating Current Set-5

Question Bank Preview

More Quizzes for Class 12

Chemistry

Mathematics

Physics