Alternating Current – 100 Advanced & Numerical with Answers & Explanations | Board & MDCAT Preparation

100 Advanced & Numerical MCQs (Level -2) on Alternating Current, Physics (Unit-Wise MCQs Practice):

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👉Physics MCQs Hub – Unit wise Physics MCQs Practice (Main-Page)👈

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Whether you are preparing for board examinations, chapter tests, college assessments, or competitive entrance exams (MDCAT, ECAT, NUST, PIEAS, GIKI, UET, FAST, and other engineering or medical admission tests), this comprehensive Alternating Current MCQ collection is designed to help you master AC circuits, resonance, transformers, and electromagnetic applications. The questions are arranged progressively—from basic concepts to advanced numerical problems and higher-order thinking—ensuring complete and systematic preparation for every type of examination.

This chapter-wise MCQ collection includes:

• 100 Basic MCQs Level-1 (1–100) – Covering AC fundamentals, sinusoidal waveforms, RMS and average values, phase difference, and basic AC circuits.
• 100 Advanced & Numerical MCQs (101–200) – Focusing on reactance, impedance, RL, RC & RLC circuits, resonance, power factor, transformers, and numerical problem-solving.
• 50 Higher-Order Thinking Skills (HOTS) MCQs (201–250) – Designed to strengthen conceptual understanding, analytical reasoning, and real-world applications.
• 50 Challenging MCQs Quiz with Answers – A carefully selected mix of conceptual, numerical, and HOTS questions for quick revision, self-assessment, and exam practice.

This MCQ collection covers:

• Alternating voltage and current
• RMS, average, and peak values
• Phase difference and AC terminology
• Resistance, inductance, capacitance, and reactance
• RL, RC & RLC circuits
• Impedance, resonance, and Q-factor
• AC power and power factor
• Choke coil and transformers
• Maximum Power Transfer Theorem
• Maxwell's equations and electromagnetic waves
• Electrocardiograph (ECG) and practical applications

Every MCQ includes the correct answer with a clear concept-based explanation to strengthen understanding, improve problem-solving skills, and reinforce key physics concepts.

This question bank helps students to:

• Build a strong conceptual foundation
• Master AC circuits and resonance
• Improve numerical and analytical skills
• Develop higher-order thinking abilities
• Avoid common examination mistakes
• Increase speed, accuracy, and confidence
• Prepare effectively for both board and competitive examinations

With 250 carefully selected MCQs and an additional 50 Challenging MCQs Quiz, this all-in-one MCQ bank provides complete preparation for Alternating Current and serves as an excellent resource for achieving success in both board examinations and competitive engineering and medical entrance tests.

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Alternating Current MCQs Level 2 – 100 Advanced & Numerical MCQs (MCQs 101–200)

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MCQ No. 101

Question: An alternating current completes 100 cycles in 2 seconds. What is its frequency?

a) 25 Hz

b) 50 Hz

c) 100 Hz

d) 200 Hz

Correct answer: b) 50 Hz

Explanation: Frequency is the number of cycles completed per second.

$$f=\frac{100}{2}=50\text{ Hz}$$

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MCQ No. 102

Question: The time period of an AC source having a frequency of 50 Hz is:

a) 0.01 s

b) 0.02 s

c) 0.05 s

d) 0.20 s

Correct answer: b) 0.02 s

Explanation:

$$T=\frac1f=\frac1{50}=0.02\text{ s}$$

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MCQ No. 103

Question: An AC source has a time period of 0.01 s. Its frequency is:

a) 25 Hz

b) 50 Hz

c) 100 Hz

d) 200 Hz

Correct answer: c) 100 Hz

Explanation:

$$f=\frac1T=\frac1{0.01}=100\text{ Hz}$$

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MCQ No. 104

Question: Calculate the angular frequency of a 50 Hz AC source.

a) 157 rad/s

b) 314 rad/s

c) 628 rad/s

d) 100 rad/s

Correct answer: b) 314 rad/s

Explanation:

$$\omega=2\pi f =2\pi(50) =314\text{ rad/s}$$

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MCQ No. 105

Question: A sinusoidal current has a peak value of 20 A. Its RMS value is:

a) 10 A

b) 12.7 A

c) 14.1 A

d) 20 A

Correct answer: c) 14.1 A

Explanation:

$$I_{rms}=\frac{20}{\sqrt2}=14.14\text{ A}$$

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MCQ No. 106

Question: An AC supply has a peak voltage of 325 V. What is its RMS voltage?

a) 110 V

b) 220 V

c) 230 V

d) 325 V

Correct answer: c) 230 V

Explanation:

$$V_{rms}=\frac{325}{\sqrt2}\approx230\text{ V}$$

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MCQ No. 107

Question: If the RMS current through a resistor is 5 A, the peak current is:

a) 5 A

b) 6.5 A

c) 7.07 A

d) 10 A

Correct answer: c) 7.07 A

Explanation:

$$I_0=\sqrt2I_{rms} =1.414\times5 =7.07\text{ A}$$

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MCQ No. 108

Question: A sinusoidal voltage has a peak value of 200 V. Its average value over one half-cycle is:

a) 100 V

b) 127.4 V

c) 141.4 V

d) 200 V

Correct answer: b) 127.4 V

Explanation:

$$V_{avg}=0.637V_0 =0.637\times200 =127.4\text{ V}$$

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MCQ No. 109

Question: A current is given by $I=15\sin\omega t$. The maximum current is:

a) 10 A

b) 15 A

c) 21.2 A

d) 30 A

Correct answer: b) 15 A

Explanation: The coefficient of the sine function represents the peak current.

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MCQ No. 110

Question: The RMS value of a current represented by $I=10\sin\omega t$ is:

a) 5 A

b) 6.37 A

c) 7.07 A

d) 10 A

Correct answer: c) 7.07 A

Explanation:

$$I_{rms}=\frac{10}{\sqrt2}=7.07\text{ A}$$

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MCQ No. 111

Question: Find the inductive reactance of a 0.20 H inductor connected to a 50 Hz supply.

a) 31.4 Ω

b) 62.8 Ω

c) 125.6 Ω

d) 15.7 Ω

Correct answer: b) 62.8 Ω

Explanation:

$$X_L=2\pi fL =2\pi(50)(0.2) =62.8\Omega$$

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MCQ No. 112

Question: An inductor has an inductive reactance of 157 Ω at 50 Hz. Its inductance is:

a) 0.25 H

b) 0.50 H

c) 1.0 H

d) 2.0 H

Correct answer: b) 0.50 H

Explanation:

$$L=\frac{X_L}{2\pi f} =\frac{157}{314} =0.50\text{ H}$$

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MCQ No. 113

Question: A capacitor of $100\mu F$ is connected to a 50 Hz supply. Its capacitive reactance is closest to:

a) 15.9 Ω

b) 31.8 Ω

c) 63.7 Ω

d) 100 Ω

Correct answer: b) 31.8 Ω

Explanation:

$$X_C=\frac1{2\pi fC} =\frac1{2\pi(50)(100\times10^{-6})} =31.8\Omega$$

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MCQ No. 114

Question: When the frequency of an AC source is doubled, the inductive reactance becomes:

a) Half

b) Double

c) Four times

d) Unchanged

Correct answer: b) Double

Explanation: Since

$$X_L=2\pi fL,$$

inductive reactance is directly proportional to frequency.

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MCQ No. 115

Question: When the frequency of an AC source is doubled, the capacitive reactance becomes:

a) Double

b) Four times

c) Half

d) Unchanged

Correct answer: c) Half

Explanation: Since

$$X_C=\frac1{2\pi fC},$$

capacitive reactance is inversely proportional to frequency.

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MCQ No. 116

Question: A resistor of 20 Ω is connected to a 100 V (RMS) AC supply. The RMS current is:

a) 2 A

b) 5 A

c) 10 A

d) 20 A

Correct answer: b) 5 A

Explanation:

$$I=\frac{V}{R} =\frac{100}{20} =5\text{ A}$$

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MCQ No. 117

Question: The average power consumed by a 100 Ω resistor carrying an RMS current of 2 A is:

a) 100 W

b) 200 W

c) 300 W

d) 400 W

Correct answer: d) 400 W

Explanation:

$$P=I^2R =(2)^2(100) =400\text{ W}$$

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MCQ No. 118

Question: A 220 V AC supply delivers 5 A to a purely resistive load. The power consumed is:

a) 220 W

b) 550 W

c) 1100 W

d) 2200 W

Correct answer: c) 1100 W

Explanation:

$$P=VI =220\times5 =1100\text{ W}$$

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MCQ No. 119

Question: A sinusoidal current has an RMS value of 8 A. The peak current is approximately:

a) 8 A

b) 9.8 A

c) 11.3 A

d) 16 A

Correct answer: c) 11.3 A

Explanation:

$$I_0=\sqrt2\times8 =11.3\text{ A}$$

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MCQ No. 120

Question: A 50 Hz AC supply completes how many cycles in one minute?

a) 500

b) 1500

c) 3000

d) 6000

Correct answer: c) 3000

Explanation:

$$\text{Number of cycles}=f\times t =50\times60 =3000$$

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MCQ No. 121

Question: An RL series circuit has a resistance of 30 Ω and an inductive reactance of 40 Ω. The impedance of the circuit is:

a) 30 Ω

b) 40 Ω

c) 50 Ω

d) 70 Ω

Correct answer: c) 50 Ω

Explanation: The impedance is

$$Z=\sqrt{R^2+X_L^2} =\sqrt{30^2+40^2} =\sqrt{2500}=50\Omega.$$

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MCQ No. 122

Question: A resistor of 60 Ω is connected in series with an inductor having $X_L=80\ \Omega$. The impedance is:

a) 80 Ω

b) 100 Ω

c) 120 Ω

d) 140 Ω

Correct answer: b) 100 Ω

Explanation:

$$Z=\sqrt{60^2+80^2} =\sqrt{10000} =100\Omega.$$

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MCQ No. 123

Question: An RL circuit has $R=24\ \Omega$ and $X_L=18\ \Omega$. Calculate the impedance.

a) 24 Ω

b) 30 Ω

c) 36 Ω

d) 42 Ω

Correct answer: b) 30 Ω

Explanation:

$$Z=\sqrt{24^2+18^2} =\sqrt{900} =30\Omega.$$

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MCQ No. 124

Question: In an RL series circuit, if the impedance is 50 Ω and the resistance is 30 Ω, the inductive reactance is:

a) 20 Ω

b) 30 Ω

c) 40 Ω

d) 50 Ω

Correct answer: c) 40 Ω

Explanation:

$$X_L=\sqrt{Z^2-R^2} =\sqrt{50^2-30^2} =\sqrt{1600} =40\Omega.$$

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MCQ No. 125

Question: A 200 V AC supply is connected across an RL circuit having an impedance of 40 Ω. The current is:

a) 2 A

b) 4 A

c) 5 A

d) 8 A

Correct answer: c) 5 A

Explanation:

$$I=\frac{V}{Z} =\frac{200}{40} =5\text{ A}.$$

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MCQ No. 126

Question: The power factor of an RL circuit having $R=30\ \Omega$ and $Z=50\ \Omega$ is:

a) 0.4

b) 0.5

c) 0.6

d) 0.8

Correct answer: c) 0.6

Explanation:

$$\cos\phi=\frac{R}{Z} =\frac{30}{50} =0.6.$$

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MCQ No. 127

Question: If the power factor of an AC circuit is 1, the phase angle is:

a) 0°

b) 30°

c) 45°

d) 90°

Correct answer: a) 0°

Explanation: A power factor of unity indicates that voltage and current are in phase.

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MCQ No. 128

Question: A circuit has a power factor of zero. It is most likely:

a) Purely resistive

b) Purely inductive or purely capacitive

c) RL circuit

d) RC circuit

Correct answer: b) Purely inductive or purely capacitive

Explanation: In purely inductive or capacitive circuits, the phase difference is $90^\circ$, making the power factor zero.

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MCQ No. 129

Question: An RC series circuit has $R=8\ \Omega$ and $X_C=6\ \Omega$. Its impedance is:

a) 8 Ω

b) 10 Ω

c) 12 Ω

d) 14 Ω

Correct answer: b) 10 Ω

Explanation:

$$Z=\sqrt{R^2+X_C^2} =\sqrt{8^2+6^2} =\sqrt{100} =10\Omega.$$

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MCQ No. 130

Question: An RC circuit has an impedance of 25 Ω and resistance of 15 Ω. The capacitive reactance is:

a) 10 Ω

b) 15 Ω

c) 20 Ω

d) 25 Ω

Correct answer: c) 20 Ω

Explanation:

$$X_C=\sqrt{25^2-15^2} =\sqrt{400} =20\Omega.$$

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MCQ No. 131

Question: A 100 V supply is connected to an RC circuit having an impedance of 20 Ω. The current is:

a) 2 A

b) 4 A

c) 5 A

d) 10 A

Correct answer: c) 5 A

Explanation:

$$I=\frac{100}{20}=5\text{ A}.$$

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MCQ No. 132

Question: In an RL circuit, the current is:

a) Ahead of the voltage

b) Behind the voltage

c) In phase with the voltage

d) Independent of the voltage

Correct answer: b) Behind the voltage

Explanation: Due to inductive reactance, current lags the voltage.

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MCQ No. 133

Question: In an RC circuit, the current is:

a) In phase with the voltage

b) Behind the voltage

c) Ahead of the voltage

d) Equal to zero

Correct answer: c) Ahead of the voltage

Explanation: In a capacitive circuit, current leads the voltage.

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MCQ No. 134

Question: If the resistance in an RL circuit increases while inductive reactance remains constant, the power factor:

a) Decreases

b) Increases

c) Remains constant

d) Becomes zero

Correct answer: b) Increases

Explanation: Since

$$\cos\phi=\frac{R}{Z},$$

an increase in resistance increases the power factor.

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MCQ No. 135

Question: An RL circuit has $R=40\ \Omega$ and $X_L=30\ \Omega$. The power factor is:

a) 0.6

b) 0.7

c) 0.8

d) 0.9

Correct answer: c) 0.8

Explanation:

$$Z=\sqrt{40^2+30^2}=50\Omega$$
$$\cos\phi=\frac{40}{50}=0.8.$$

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MCQ No. 136

Question: The phase angle of an RL circuit increases when:

a) Resistance increases

b) Inductive reactance increases

c) Frequency decreases

d) Voltage decreases

Correct answer: b) Inductive reactance increases

Explanation: Since

$$\tan\phi=\frac{X_L}{R},$$

a larger inductive reactance results in a greater phase angle.

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MCQ No. 137

Question: Which quantity is represented by the hypotenuse of the impedance triangle?

a) Resistance

b) Reactance

c) Impedance

d) Power factor

Correct answer: c) Impedance

Explanation: In the impedance triangle, impedance is the resultant of resistance and reactance.

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MCQ No. 138

Question: In an impedance triangle, the horizontal side represents:

a) Inductive reactance

b) Capacitive reactance

c) Resistance

d) Impedance

Correct answer: c) Resistance

Explanation: Resistance is plotted along the horizontal axis, while reactance is plotted vertically.

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MCQ No. 139

Question: The vertical side of an RL impedance triangle represents:

a) Resistance

b) Inductive reactance

c) Impedance

d) Power

Correct answer: b) Inductive reactance

Explanation: The vertical side of the impedance triangle represents inductive reactance in an RL circuit.

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MCQ No. 140

Question: A 240 V AC source is connected to a circuit having an impedance of 60 Ω. The RMS current is:

a) 2 A

b) 3 A

c) 4 A

d) 5 A

Correct answer: c) 4 A

Explanation:

$$I=\frac{V}{Z} =\frac{240}{60} =4\text{ A}.$$

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MCQ No. 141

Question: An RLC series circuit has $R=30\,\Omega$, $X_L=50\,\Omega$, and $X_C=20\,\Omega$. The net reactance is:

a) 20 Ω

b) 30 Ω

c) 50 Ω

d) 70 Ω

Correct answer: b) 30 Ω

Explanation: Net reactance is

$$X=X_L-X_C=50-20=30\,\Omega.$$

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MCQ No. 142

Question: For the circuit in MCQ 141, the impedance is:

a) 30 Ω

b) 42.4 Ω

c) 50 Ω

d) 60 Ω

Correct answer: b) 42.4 Ω

Explanation:

$$Z=\sqrt{R^2+(X_L-X_C)^2} =\sqrt{30^2+30^2} =\sqrt{1800} \approx42.4\,\Omega.$$

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MCQ No. 143

Question: A 212 V (RMS) supply is connected to the circuit in MCQ 142. The RMS current is approximately:

a) 2 A

b) 3 A

c) 5 A

d) 7 A

Correct answer: c) 5 A

Explanation:

$$I=\frac{V}{Z} =\frac{212}{42.4} =5\,\text{A}.$$

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MCQ No. 144

Question: In a series RLC circuit, resonance occurs when:

a) $R=X_L$

b) $R=X_C$

c) $X_L=X_C$

d) $R=0$

Correct answer: c) $X_L=X_C$

Explanation: At resonance, inductive and capacitive reactances are equal, so the net reactance becomes zero.

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MCQ No. 145

Question: At resonance, the impedance of a series RLC circuit is equal to:

a) $X_L$

b) $X_C$

c) Resistance only

d) Zero

Correct answer: c) Resistance only

Explanation: Since $X_L=X_C$, the reactances cancel each other, leaving only the resistance.

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MCQ No. 146

Question: A series RLC circuit has $R=20\,\Omega$. At resonance, its impedance is:

a) 0 Ω

b) 10 Ω

c) 20 Ω

d) 40 Ω

Correct answer: c) 20 Ω

Explanation: At resonance,

$$Z=R=20\,\Omega.$$

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MCQ No. 147

Question: A 200 V AC source is connected to the circuit in MCQ 146. The current at resonance is:

a) 2 A

b) 5 A

c) 10 A

d) 20 A

Correct answer: c) 10 A

Explanation:

$$I=\frac{V}{R} =\frac{200}{20} =10\,\text{A}.$$

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MCQ No. 148

Question: The resonant frequency of an RLC circuit depends upon:

a) Resistance only

b) Inductance and capacitance

c) Voltage only

d) Current only

Correct answer: b) Inductance and capacitance

Explanation: Resonant frequency is determined by:

$$f_0=\frac{1}{2\pi\sqrt{LC}}.$$

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MCQ No. 149

Question: If the inductance of a resonant circuit is doubled while capacitance remains unchanged, the resonant frequency will:

a) Increase

b) Remain unchanged

c) Decrease

d) Become zero

Correct answer: c) Decrease

Explanation: Since

$$f_0\propto\frac1{\sqrt{L}},$$

increasing inductance decreases the resonant frequency.

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MCQ No. 150

Question: If the capacitance of a resonant circuit is increased four times, the resonant frequency becomes:

a) Four times

b) Twice

c) Half

d) One-fourth

Correct answer: c) Half

Explanation: Since

$$f_0\propto\frac1{\sqrt{C}},$$

quadrupling capacitance halves the resonant frequency.

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MCQ No. 151

Question: The resonant frequency of an RLC circuit with $L=0.2\,H$ and $C=50\,\mu F$ is approximately:

a) 25 Hz

b) 50 Hz

c) 100 Hz

d) 500 Hz

Correct answer: b) 50 Hz

Explanation:

$$f_0=\frac1{2\pi\sqrt{LC}} =\frac1{2\pi\sqrt{0.2\times50\times10^{-6}}} \approx50\,\text{Hz}.$$

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MCQ No. 152

Question: The quality factor (Q-factor) of a resonant circuit mainly indicates:

a) Supply voltage

b) Power consumption

c) Sharpness of resonance

d) Frequency of AC source

Correct answer: c) Sharpness of resonance

Explanation: A higher Q-factor means sharper resonance and better frequency selectivity.

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MCQ No. 153

Question: A high Q-factor indicates:

a) Large energy losses

b) Poor selectivity

c) Small energy losses

d) Zero inductance

Correct answer: c) Small energy losses

Explanation: High-quality circuits store energy efficiently with minimal losses.

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MCQ No. 154

Question: At resonance, the power factor of a series RLC circuit is:

a) Zero

b) 0.5

c) 0.707

d) 1

Correct answer: d) 1

Explanation: At resonance, current and voltage are in phase, giving a unity power factor.

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MCQ No. 155

Question: An AC circuit has $V=240\,V$, $I=5\,A$, and power factor $=0.8$ The average power consumed is:

a) 480 W

b) 768 W

c) 960 W

d) 1200 W

Correct answer: c) 960 W

Explanation:

$$P=VI\cos\phi =240\times5\times0.8 =960\,W.$$

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MCQ No. 156

Question: A circuit draws 4 A from a 220 V supply with unity power factor. The power consumed is:

a) 220 W

b) 440 W

c) 660 W

d) 880 W

Correct answer: d) 880 W

Explanation:

$$P=VI =220\times4 =880\,W.$$

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MCQ No. 157

Question: If the power factor decreases while voltage and current remain constant, the real power:

a) Increases

b) Decreases

c) Remains unchanged

d) Becomes zero immediately

Correct answer: b) Decreases

Explanation: Real power is given by

$$P=VI\cos\phi.$$

A lower power factor means less useful power.

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MCQ No. 158

Question: Maximum power is transferred to the load when:

a) Load resistance is zero

b) Source resistance is zero

c) Load impedance matches source impedance

d) Load resistance is infinite

Correct answer: c) Load impedance matches source impedance

Explanation: According to the Maximum Power Transfer Theorem, maximum power is delivered when the load impedance equals the source impedance.

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MCQ No. 159

Question: Which device commonly uses the principle of resonance to select a desired frequency?

a) Electric heater

b) Radio receiver

c) Electric bell

d) Ammeter

Correct answer: b) Radio receiver

Explanation: Radio receivers use resonant circuits to tune and select the desired broadcasting frequency while rejecting others.

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MCQ No. 160

Question: In a series RLC circuit operating exactly at resonance, which statement is correct?

a) Current is minimum and impedance is maximum.

b) Current is maximum and impedance is minimum.

c) Current is zero and impedance is infinite.

d) Voltage and current differ by $90^\circ$.

Correct answer: b) Current is maximum and impedance is minimum.

Explanation: At resonance, $X_L=X_C$, so the net reactance becomes zero. The impedance reduces to the resistance alone, resulting in maximum current and a phase difference of $0^\circ$

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MCQ No. 161

Question: A series RLC circuit has $R=40\,\Omega$ , $X_L=90\,\Omega$ , and $X_C=50\,\Omega$ . The impedance of the circuit is:

a) 40 Ω

b) 50 Ω

c) 56.6 Ω

d) 90 Ω

Correct answer: c) 56.6 Ω

Explanation: The net reactance is:

$$X=X_L-X_C=90-50=40\,\Omega$$

Hence,

$$Z=\sqrt{R^2+X^2} =\sqrt{40^2+40^2} =\sqrt{3200} \approx56.6\,\Omega.$$

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MCQ No. 162

Question: A 283 V (RMS) AC source is connected to the circuit in MCQ 161. The RMS current is:

a) 2 A

b) 3 A

c) 5 A

d) 7 A

Correct answer: c) 5 A

Explanation:

$$I=\frac{V}{Z} =\frac{283}{56.6} =5\,A.$$

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MCQ No. 163

Question: The power factor of the circuit in MCQ 161 is:

a) 0.50

b) 0.60

c) 0.71

d) 0.90

Correct answer: c) 0.71

Explanation:

$$\cos\phi=\frac{R}{Z} =\frac{40}{56.6} \approx0.71.$$

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MCQ No. 164

Question: An RLC circuit has $L=0.10\,H$  and $C=100\,\mu F$ . The resonant frequency is approximately:

a) 25 Hz

b) 50 Hz

c) 100 Hz

d) 160 Hz

Correct answer: b) 50 Hz

Explanation:

$$f_0=\frac{1}{2\pi\sqrt{LC}} =\frac{1}{2\pi\sqrt{0.10\times100\times10^{-6}}} \approx50.3\,Hz.$$

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MCQ No. 165

Question: If the frequency of an AC source is doubled, the inductive reactance becomes:

a) Half

b) Double

c) Four times

d) Unchanged

Correct answer: b) Double

Explanation: Since

$$X_L=2\pi fL,$$

inductive reactance is directly proportional to frequency.

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MCQ No. 166

Question: If the frequency of an AC source is doubled, the capacitive reactance becomes:

a) Double

b) Four times

c) Half

d) Unchanged

Correct answer: c) Half

Explanation: Capacitive reactance is inversely proportional to frequency:

$$X_C=\frac1{2\pi fC}.$$

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MCQ No. 167

Question: A capacitor of $50\,\mu F$  is connected to a 50 Hz supply. The capacitive reactance is closest to:

a) 31.8 Ω

b) 63.7 Ω

c) 95.5 Ω

d) 127 Ω

Correct answer: b) 63.7 Ω

Explanation:

$$X_C=\frac1{2\pi(50)(50\times10^{-6})} \approx63.7\,\Omega.$$

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MCQ No. 168

Question: An inductor of 0.5 H is connected to a 100 Hz supply. The inductive reactance is:

a) 157 Ω

b) 314 Ω

c) 628 Ω

d) 100 Ω

Correct answer: b) 314 Ω

Explanation:

$$X_L=2\pi(100)(0.5) =314\,\Omega.$$

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MCQ No. 169

Question: A series RLC circuit is at resonance. If the applied voltage is doubled, the current will:

a) Become half

b) Remain unchanged

c) Double

d) Become four times

Correct answer: c) Double

Explanation: At resonance,

$$I=\frac{V}{R}.$$

Current is directly proportional to voltage.

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MCQ No. 170

Question: A resistor consumes 400 W from a 200 V RMS supply. The current is:

a) 1 A

b) 2 A

c) 4 A

d) 8 A

Correct answer: b) 2 A

Explanation:

$$P=VI$$
$$I=\frac{400}{200}=2\,A.$$

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MCQ No. 171

Question: The power factor of a purely inductive circuit is:

a) 0

b) 0.5

c) 0.707

d) 1

Correct answer: a) 0

Explanation: In a purely inductive circuit, the phase angle is $90^\circ$, so

$$\cos90^\circ=0.$$

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MCQ No. 172

Question: The power factor of a purely capacitive circuit is:

a) 0

b) 0.5

c) 0.707

d) 1

Correct answer: a) 0

Explanation: Since the phase difference is $90^\circ$, the average power consumed is zero.

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MCQ No. 173

Question: A series RLC circuit has $R=25\,\Omega$  and is operating at resonance with a current of 4 A. The supply voltage is:

a) 50 V

b) 75 V

c) 100 V

d) 125 V

Correct answer: c) 100 V

Explanation:

$$V=IR =4\times25 =100\,V.$$

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MCQ No. 174

Question: The impedance of a purely resistive AC circuit is:

a) Less than resistance

b) Equal to resistance

c) Greater than resistance

d) Zero

Correct answer: b) Equal to resistance

Explanation: Since there is no reactance,

$$Z=R.$$

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MCQ No. 175

Question: A resistor of 50 Ω is connected to a 250 V RMS AC supply. The power consumed is:

a) 500 W

b) 1000 W

c) 1250 W

d) 2500 W

Correct answer: c) 1250 W

Explanation:

$$P=\frac{V^2}{R} =\frac{250^2}{50} =1250\,W.$$

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MCQ No. 176

Question: Which quantity remains unchanged when an AC source passes through an ideal transformer?

a) Voltage

b) Current

c) Frequency

d) Power

Correct answer: c) Frequency

Explanation: A transformer changes voltage and current but does not alter the frequency of the AC supply.

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MCQ No. 177

Question: An ideal choke coil is preferred over a resistor for limiting AC current because it:

a) Produces more heat

b) Has greater resistance

c) Wastes very little power

d) Increases voltage

Correct answer: c) Wastes very little power

Explanation: A choke coil limits current using inductive reactance rather than resistance, so very little electrical energy is converted into heat.

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MCQ No. 178

Question: Which of the following devices relies primarily on the resonance of an RLC circuit?

a) Electric iron

b) Radio tuner

c) Electric heater

d) Ammeter

Correct answer: b) Radio tuner

Explanation: Radio receivers use resonant circuits to select the desired station frequency while rejecting others.

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MCQ No. 179

Question: If the inductive reactance is greater than the capacitive reactance in an RLC circuit, the circuit behaves as:

a) Purely resistive

b) Capacitive

c) Inductive

d) Open circuit

Correct answer: c) Inductive

Explanation: When $X_L>X_C$, the net reactance is inductive, and the current lags the voltage.

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MCQ No. 180

Question: A series RLC circuit has $X_L=120\,\Omega$  and $X_C=120\,\Omega$. Which statement is correct?

a) The circuit is purely inductive.

b) The circuit is purely capacitive.

c) The circuit is at resonance and behaves as a purely resistive circuit.

d) The current becomes zero.

Correct answer: c) The circuit is at resonance and behaves as a purely resistive circuit.

Explanation: Since

$$X_L=X_C,$$

the reactances cancel each other. The impedance equals the resistance only, the current is maximum, and the power factor is unity.

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MCQ No. 181

Question: A series RLC circuit has $R=30\,\Omega$, $X_L=80\,\Omega$, and $X_C=20\,\Omega$. The impedance of the circuit is:

a) 30 Ω

b) 50 Ω

c) 67.1 Ω

d) 100 Ω

Correct answer: c) 67.1 Ω

Explanation:
The net reactance is:

$$X=X_L-X_C=80-20=60\,\Omega$$

Therefore,

$$Z=\sqrt{R^2+X^2} =\sqrt{30^2+60^2} =\sqrt{4500} \approx67.1\,\Omega.$$

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MCQ No. 182

Question: A 335.5 V RMS supply is connected to the circuit in MCQ 181. The RMS current is:

a) 2 A

b) 3 A

c) 5 A

d) 6 A

Correct answer: c) 5 A

Explanation:

$$I=\frac{V}{Z} =\frac{335.5}{67.1} =5\,A.$$

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MCQ No. 183

Question: The power factor of the circuit in MCQ 181 is:

a) 0.25

b) 0.45

c) 0.60

d) 0.80

Correct answer: b) 0.45

Explanation:

$$\cos\phi=\frac{R}{Z} =\frac{30}{67.1} \approx0.447\approx0.45.$$

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MCQ No. 184

Question: A resistor of 40 Ω is connected in series with a capacitor having $X_C=30\,\Omega$ . The impedance of the circuit is:

a) 40 Ω

b) 50 Ω

c) 60 Ω

d) 70 Ω

Correct answer: b) 50 Ω

Explanation:

$$Z=\sqrt{R^2+X_C^2} =\sqrt{40^2+30^2} =50\,\Omega.$$

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MCQ No. 185

Question: A 250 V RMS source is connected across the circuit in MCQ 184. The RMS current is:

a) 2 A

b) 4 A

c) 5 A

d) 6.25 A

Correct answer: c) 5 A

Explanation:

$$I=\frac{250}{50}=5\,A.$$

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MCQ No. 186

Question: An RLC circuit has $L=0.20\,H$and $C=12.7\,\mu F$. The resonant frequency is closest to:

a) 50 Hz

b) 75 Hz

c) 100 Hz

d) 150 Hz

Correct answer: c) 100 Hz

Explanation:

$$f_0=\frac{1}{2\pi\sqrt{LC}} =\frac{1}{2\pi\sqrt{0.20\times12.7\times10^{-6}}} \approx100\,Hz.$$

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MCQ No. 187

Question: At resonance, which quantity is minimum in a series RLC circuit?

a) Current

b) Voltage

c) Impedance

d) Power

Correct answer: c) Impedance

Explanation: At resonance, $X_L=X_C$, so the impedance becomes equal to the resistance only and is minimum.

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MCQ No. 188

Question: A series RLC circuit has $R=25\,\Omega$. At resonance, a current of 8 A flows. The supply voltage is:

a) 100 V

b) 150 V

c) 200 V

d) 250 V

Correct answer: c) 200 V

Explanation:

$$V=IR =8\times25 =200\,V.$$

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MCQ No. 189

Question: An AC source of 240 V supplies a current of 6 A with a power factor of 0.8. The average power consumed is:

a) 960 W

b) 1000 W

c) 1152 W

d) 1440 W

Correct answer: c) 1152 W

Explanation:

$$P=VI\cos\phi =240\times6\times0.8 =1152\,W.$$

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MCQ No. 190

Question: A circuit consumes 1000 W from a 250 V supply with a power factor of 0.8. The RMS current is:

a) 4 A

b) 5 A

c) 6.25 A

d) 8 A

Correct answer: b) 5 A

Explanation:

$$I=\frac{P}{V\cos\phi} =\frac{1000}{250\times0.8} =5\,A.$$

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MCQ No. 191

Question: If the inductance of a resonant circuit becomes four times larger while capacitance remains unchanged, the resonant frequency becomes:

a) Four times

b) Twice

c) Half

d) One-fourth

Correct answer: c) Half

Explanation: Since

$$f_0\propto\frac{1}{\sqrt{L}},$$

quadrupling the inductance reduces the resonant frequency to one-half.

---

MCQ No. 192

Question: Which quantity remains unchanged in an ideal transformer?

a) Voltage

b) Current

c) Frequency

d) Power factor

Correct answer: c) Frequency

Explanation: An ideal transformer changes voltage and current but does not change the frequency of the alternating supply.

---

MCQ No. 193

Question: A 220 V AC supply is connected to a 44 Ω resistor. The current is:

a) 2 A

b) 4 A

c) 5 A

d) 10 A

Correct answer: c) 5 A

Explanation:

$$I=\frac{220}{44}=5\,A.$$

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MCQ No. 194

Question: The power consumed by the resistor in MCQ 193 is:

a) 550 W

b) 880 W

c) 1100 W

d) 2200 W

Correct answer: c) 1100 W

Explanation:

$$P=VI =220\times5 =1100\,W.$$

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MCQ No. 195

Question: Which of the following devices primarily uses alternating current at its input?

a) Dry cell

b) Transformer

c) Lead-acid battery

d) Solar cell

Correct answer: b) Transformer

Explanation: A transformer operates only with alternating current because it depends on a changing magnetic flux to induce emf.

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MCQ No. 196

Question: The SI unit of impedance is:

a) Henry

b) Farad

c) Ohm

d) Weber

Correct answer: c) Ohm

Explanation: Impedance, like resistance and reactance, is measured in ohms (Ω).

---

MCQ No. 197

Question: A high Q-factor of a resonant circuit indicates:

a) Greater energy loss

b) Lower efficiency

c) Better selectivity and lower energy loss

d) Lower resonant frequency

Correct answer: c) Better selectivity and lower energy loss

Explanation: A high-quality factor produces sharp resonance and efficient energy storage with minimal losses.

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MCQ No. 198

Question: Maxwell's equations predict the existence of:

a) Sound waves

b) Mechanical waves

c) Electromagnetic waves

d) Water waves

Correct answer: c) Electromagnetic waves

Explanation: Maxwell showed that changing electric and magnetic fields propagate through space as electromagnetic waves.

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MCQ No. 199

Question: Electromagnetic waves travel in free space with a speed of approximately:

a) $3\times10^6$

b) $3\times10^7$

c) $3\times10^8$

d) $3\times10^9$

Correct answer: c) $3\times10^8$

Explanation: Electromagnetic waves propagate in a vacuum at the speed of light,

$$c=3\times10^8\,\text{m/s}.$$

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MCQ No. 200

Question: Which statement best explains why alternating current is preferred for long-distance power transmission?

a) It cannot be transformed.

b) It always has lower current than DC.

c) Its voltage can be stepped up to reduce transmission losses and stepped down for safe distribution.

d) It travels faster than direct current.

Correct answer: c) Its voltage can be stepped up to reduce transmission losses and stepped down for safe distribution.

Explanation: AC voltage can be increased using step-up transformers, reducing current and minimizing power loss $(P_{\text{loss}}=I^2R)$ in transmission lines. It is then reduced to safer levels by step-down transformers before reaching consumers. This ability makes AC the most economical choice for modern electrical power systems.

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