100 Important Basic MCQs (Level -1) on Alternating Current, Physics (Unit-Wise MCQs Practice):

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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.

Alternating Current MCQs Level 1 – 100 Basic MCQs (1–100)

MCQ No. 1

Question: What is an alternating current (AC)?

a) A current that always flows in one direction

b) A current that changes both magnitude and direction periodically

c) A current that remains constant with time

d) A current produced only by batteries

Correct answer: b) A current that changes both magnitude and direction periodically

Explanation: Alternating current (AC) is an electric current whose magnitude and direction change periodically with time. It is the standard form of electrical energy supplied to homes and industries.

MCQ No. 2

Question: Which of the following is the main source of alternating current?

a) Dry cell

b) Battery

c) AC generator (Alternator)

d) Solar cell

Correct answer: c) AC generator (Alternator)

Explanation: Alternating current is produced by AC generators (alternators), whereas batteries and cells produce direct current (DC).

MCQ No. 3

Question: Which type of graph best represents an ideal alternating current?

a) Straight line

b) Triangular wave

c) Sinusoidal wave

d) Rectangular wave

Correct answer: c) Sinusoidal wave

Explanation: An ideal alternating current varies sinusoidally with time and is represented by a sine curve.

MCQ No. 4

Question: During one complete cycle of AC, the current changes its direction:

a) Once

b) Twice

c) Three times

d) Four times

Correct answer: b) Twice

Explanation: During one complete cycle, AC flows in the positive direction during one half-cycle and in the opposite direction during the next half-cycle.

MCQ No. 5

Question: The time taken by an AC waveform to complete one full cycle is called:

a) Frequency

b) Amplitude

c) Time period

d) Phase angle

Correct answer: c) Time period

Explanation: The time period (T) is the time required for one complete cycle of an alternating quantity.

MCQ No. 6

Question: The SI unit of time period is:

a) Hertz

b) Second

c) Volt

d) Ampere

Correct answer: b) Second

Explanation: Time period is measured in seconds (s).

MCQ No. 7

Question: Frequency is defined as:

a) Number of oscillations per minute

b) Number of oscillations per second

c) Voltage per second

d) Current per second

Correct answer: b) Number of oscillations per second

Explanation: Frequency represents the number of complete cycles occurring every second.

MCQ No. 8

Question: The SI unit of frequency is:

a) Ohm

b) Watt

c) Hertz

d) Coulomb

Correct answer: c) Hertz

Explanation: One hertz (Hz) means one complete cycle per second.

MCQ No. 9

Question: The frequency of domestic AC supply in Pakistan is:

a) 25 Hz

b) 40 Hz

c) 50 Hz

d) 60 Hz

Correct answer: c) 50 Hz

Explanation: The standard frequency of AC supplied in Pakistan is 50 Hz.

MCQ No. 10

Question: Which equation relates frequency and time period?

a) $f=T$

b) $f=\frac{1}{T}$

c) $f=T^2$

d) $f=2T$

Correct answer: b) $f=\frac{1}{T}$

Explanation: Frequency is the reciprocal of the time period.

MCQ No. 11

Question: Which quantity represents the maximum value of alternating current or voltage?

a) Average value

b) RMS value

c) Peak value

d) Instantaneous value

Correct answer: c) Peak value

Explanation: Peak value is the highest value attained by an alternating quantity during a cycle.

MCQ No. 12

Question: Another name for the peak value is:

a) Effective value

b) Maximum value

c) RMS value

d) Average value

Correct answer: b) Maximum value

Explanation: Peak value is also called the maximum value.

MCQ No. 13

Question: The effective value of AC is also called its:

a) Instantaneous value

b) Peak value

c) RMS value

d) Minimum value

Correct answer: c) RMS value

Explanation: RMS (Root Mean Square) value produces the same heating effect as an equivalent DC current.

MCQ No. 14

Question: RMS stands for:

a) Relative Mean Square

b) Root Mean Square

c) Root Maximum Signal

d) Random Mean Square

Correct answer: b) Root Mean Square

Explanation: RMS is the standard method of expressing the effective value of alternating voltage or current.

MCQ No. 15

Question: Which value of AC is measured by ordinary AC voltmeters?

a) Peak value

b) Instantaneous value

c) RMS value

d) Average value

Correct answer: c) RMS value

Explanation: AC voltmeters are calibrated to indicate RMS values.

MCQ No. 16

Question: In a sinusoidal AC waveform, the average value over one complete cycle is:

a) Maximum

b) Equal to RMS value

c) Zero

d) Half of peak value

Correct answer: c) Zero

Explanation: The positive and negative halves of a complete cycle cancel each other, making the average value zero.

MCQ No. 17

Question: Which quantity changes continuously in an AC circuit?

a) Only resistance

b) Only voltage

c) Both current and voltage

d) Only power

Correct answer: c) Both current and voltage

Explanation: In AC circuits, both current and voltage continuously vary in magnitude and direction.

MCQ No. 18

Question: AC is preferred over DC for long-distance power transmission because:

a) It is cheaper to generate

b) It can easily be transformed to high or low voltage

c) It has higher current

d) It has no power loss

Correct answer: b) It can easily be transformed to high or low voltage

Explanation: Transformers work only with AC, allowing efficient high-voltage transmission and reducing power losses.

MCQ No. 19

Question: Which of the following devices operates on alternating current?

a) Dry cell

b) Torch light

c) Electric ceiling fan

d) Car battery

Correct answer: c) Electric ceiling fan

Explanation: Household appliances like fans operate on AC supplied through the mains.

MCQ No. 20

Question: The waveform of an ideal AC repeats itself after every:

a) Quarter cycle

b) Half cycle

c) Complete cycle

d) Two cycles

Correct answer: c) Complete cycle

Explanation: An alternating waveform is periodic and repeats its pattern after one complete cycle.

MCQ No. 21

Question: A sinusoidal alternating current is represented mathematically by:

a) $I = I_0$

b) $I = I_0\sin\omega t$

c) $I = I_0t$

d) $I = \frac{I_0}{t}$

Correct answer: b) $I = I_0\sin\omega t$

Explanation: A sinusoidal alternating current varies according to the sine function. Here, $I_0$ is the peak current and $\omega$ is the angular frequency.

MCQ No. 22

Question: In the expression $I = I_0\sin\omega t$ , $I_0$ represents:

a) Average current

b) RMS current

c) Peak current

d) Instantaneous current

Correct answer: c) Peak current

Explanation: The symbol $I_0$ denotes the maximum or peak value of the alternating current.

MCQ No. 23

Question: In the equation $V = V_0\sin\omega t$ , $V_0$ represents:

a) Average voltage

b) RMS voltage

c) Peak voltage

d) Instantaneous voltage

Correct answer: c) Peak voltage

Explanation: $V_0$ is the maximum value of alternating voltage attained during one cycle.

MCQ No. 24

Question: The symbol $\omega$ denotes:

a) Frequency

b) Angular frequency

c) Wavelength

d) Phase angle

Correct answer: b) Angular frequency

Explanation: Angular frequency ( $\omega$ ) represents the rate of angular change of the AC waveform and is measured in rad/s.

MCQ No. 25

Question: The SI unit of angular frequency is:

a) Hertz

b) Radian per second

c) Second

d) Degree

Correct answer: b) Radian per second

Explanation: Angular frequency is measured in radians per second (rad/s).

MCQ No. 26

Question: The relationship between angular frequency and frequency is:

a) $\omega=f$

b) $\omega=2\pi f$

c) $\omega=\pi f$

d) $\omega=\frac{f}{2\pi}$

Correct answer: b) $\omega=2\pi f$

Explanation: Angular frequency is equal to $2\pi$ times the ordinary frequency.

MCQ No. 27

Question: Which quantity determines how rapidly the AC waveform oscillates?

a) Resistance

b) Angular frequency

c) Voltage

d) Current

Correct answer: b) Angular frequency

Explanation: A larger angular frequency means the waveform completes more oscillations in a given time.

MCQ No. 28

Question: The instantaneous value of AC depends upon:

a) Time

b) Resistance only

c) Inductance only

d) Capacitance only

Correct answer: a) Time

Explanation: The instantaneous value continuously changes with time according to the sine function.

MCQ No. 29

Question: Which of the following is an instantaneous value of alternating current?

a) The current at a particular instant

b) The maximum current

c) The average current

d) The RMS current

Correct answer: a) The current at a particular instant

Explanation: Instantaneous current is the value of current at any specific moment during the cycle.

MCQ No. 30

Question: The peak value of an alternating quantity occurs when:

a) $\sin\omega t=0$

b) $\sin\omega t=1$

c) $\sin\omega t=-1$

d) $\sin\omega t=\frac12$

Correct answer: b) $\sin\omega t=1$

Explanation: The sine function reaches its maximum value of +1 at the positive peak of the waveform.

MCQ No. 31

Question: The positive half-cycle of an AC wave corresponds to:

a) Positive current direction

b) Zero current

c) Negative current direction

d) Constant current

Correct answer: a) Positive current direction

Explanation: During the positive half-cycle, current flows in one chosen direction.

MCQ No. 32

Question: The negative half-cycle of an AC wave represents:

a) Increase in frequency

b) Reversal of current direction

c) Increase in resistance

d) Zero voltage

Correct answer: b) Reversal of current direction

Explanation: During the negative half-cycle, the current flows in the opposite direction.

MCQ No. 33

Question: One complete sinusoidal wave corresponds to a phase angle of:

a) $90^\circ$

b) $180^\circ$

c) $270^\circ$

d) $360^\circ$

Correct answer: d) $360^\circ$

Explanation: One complete cycle is equivalent to $360^\circ$ or $2\pi$ radians.

MCQ No. 34

Question: Half of one complete AC cycle corresponds to:

a) $45^\circ$

b) $90^\circ$

c) $180^\circ$

d) $360^\circ$

Correct answer: c) $180^\circ$

Explanation: A half-cycle covers an angular displacement of $180^\circ$ .

MCQ No. 35

Question: The phase angle is usually measured in:

a) Newton

b) Joule

c) Degrees or radians

d) Tesla

Correct answer: c) Degrees or radians

Explanation: Phase angle may be expressed in degrees (°) or radians (rad).

MCQ No. 36

Question: Two alternating quantities are said to be in phase if they:

a) Reach maximum and minimum values simultaneously

b) Have different frequencies

c) Differ by $180^\circ$

d) Never become zero together

Correct answer: a) Reach maximum and minimum values simultaneously

Explanation: Quantities in phase have zero phase difference and attain corresponding values at the same instant.

MCQ No. 37

Question: When two AC quantities are out of phase, they:

a) Always have equal amplitudes

b) Reach corresponding values at different times

c) Have zero frequency

d) Become constant

Correct answer: b) Reach corresponding values at different times

Explanation: A phase difference causes one waveform to lead or lag the other.

MCQ No. 38

Question: The phase difference between two identical sinusoidal waves in phase is:

a) $90^\circ$

b) $180^\circ$

c) $360^\circ$

d) $0^\circ$

Correct answer: d) $0^\circ$

Explanation: In-phase quantities have no phase difference.

MCQ No. 39

Question: Which instrument is commonly used to observe AC waveforms?

a) Ammeter

b) Oscilloscope (CRO)

c) Voltmeter

d) Galvanometer

Correct answer: b) Oscilloscope (CRO)

Explanation: A Cathode Ray Oscilloscope (CRO) displays voltage or current waveforms and helps measure amplitude, frequency, and phase difference.

MCQ No. 40

Question: The horizontal axis of an AC waveform graph generally represents:

a) Voltage

b) Current

c) Time

d) Resistance

Correct answer: c) Time

Explanation: AC waveforms are plotted with time on the horizontal axis and voltage or current on the vertical axis.

MCQ No. 41

Question: The peak value of an alternating current is the:

a) Average value during one cycle

b) Effective value

c) Maximum instantaneous value

d) Minimum value

Correct answer: c) Maximum instantaneous value

Explanation: The peak value is the greatest instantaneous value attained by the alternating current or voltage during a cycle.

MCQ No. 42

Question: If the peak voltage of an AC source is 100 V, then the symbol used to represent it is:

a) $V_{\text{rms}}$

b) $V_{\text{avg}}$

c) $V_0$

d) $V$

Correct answer: c) $V_0$

Explanation: The symbol $V_0$ or $V_{\text{max}}$ represents the peak (maximum) voltage.

MCQ No. 43

Question: The average value of a sinusoidal alternating current over one complete cycle is:

a) Equal to its peak value

b) Equal to its RMS value

c) Zero

d) Half of its peak value

Correct answer: c) Zero

Explanation: The positive and negative halves of a complete cycle cancel each other, giving an average value of zero.

MCQ No. 44

Question: The average value of a sinusoidal AC is usually calculated over:

a) One complete cycle

b) Half cycle

c) Two complete cycles

d) Three complete cycles

Correct answer: b) Half cycle

Explanation: Since the average over a complete cycle is zero, the average value is conventionally calculated over one half-cycle.

MCQ No. 45

Question: The average value of a sinusoidal current over one half-cycle is:

a) $0.637I_0$

b) $0.707I_0$

c) $1.414I_0$

d) $0.500I_0$

Correct answer: a) $0.637I_0$

Explanation: The average value of a sinusoidal current over one half-cycle is given by
$I_{\text{avg}}=\frac{2I_0}{\pi}\approx0.637I_0.$

MCQ No. 46

Question: The average value of a sinusoidal voltage over one half-cycle is:

a) $0.707V_0$

b) $0.637V_0$

c) $1.414V_0$

d) $0.500V_0$

Correct answer: b) $0.637V_0$

Explanation: The average value of sinusoidal voltage over one half-cycle equals $0.637V_0$

MCQ No. 47

Question: RMS stands for:

a) Relative Mean Square

b) Root Mean Square

c) Root Maximum Signal

d) Random Mean Signal

Correct answer: b) Root Mean Square

Explanation: RMS is the standard method used to express the effective value of alternating current and voltage.

MCQ No. 48

Question: The RMS value of AC is also called its:

a) Average value

b) Effective value

c) Instantaneous value

d) Peak value

Correct answer: b) Effective value

Explanation: The RMS value is called the effective value because it produces the same heating effect as an equivalent DC current.

MCQ No. 49

Question: The RMS value of a sinusoidal current is:

a) $0.637I_0$

b) $0.707I_0$

c) $1.414I_0$

d) $2I_0$

Correct answer: b) $0.707I_0$

Explanation: For a sinusoidal current,
$I_{\text{rms}}=\frac{I_0}{\sqrt2}=0.707I_0.$

MCQ No. 50

Question: The RMS value of a sinusoidal voltage is:

a) $0.707V_0$

b) $0.637V_0$

c) $1.414V_0$

d) $2V_0$

Correct answer: a) $0.707V_0$

Explanation: The RMS value of voltage is given by
$V_{\text{rms}}=\frac{V_0}{\sqrt2}.$

MCQ No. 51

Question: If the peak current is 10 A, its RMS value is approximately:

a) 5.0 A

b) 6.37 A

c) 7.07 A

d) 10 A

Correct answer: c) 7.07 A

Explanation: Since $I_{\text{rms}}=0.707I_0$ ,
$I_{\text{rms}}=0.707\times10=7.07\text{ A}.$

MCQ No. 52

Question: If the RMS voltage of an AC supply is 220 V, its peak voltage is approximately:

a) 110 V

b) 220 V

c) 311 V

d) 440 V

Correct answer: c) 311 V

Explanation: The peak voltage is
$V_0=\sqrt2V_{\text{rms}} =1.414\times220 \approx311\text{ V}.$

MCQ No. 53

Question: Which value of AC is normally specified for domestic electricity?

a) Peak value

b) Average value

c) RMS value

d) Instantaneous value

Correct answer: c) RMS value

Explanation: Household electricity ratings such as 220 V or 230 V refer to RMS values.

MCQ No. 54

Question: The RMS value of AC is important because it determines the:

a) Frequency only

b) Heating effect

c) Wavelength

d) Phase angle only

Correct answer: b) Heating effect

Explanation: RMS values are used because they produce the same heating effect in a resistor as equivalent DC values.

MCQ No. 55

Question: Which instrument is calibrated to read RMS voltage?

a) CRO

b) Ammeter

c) AC Voltmeter

d) Galvanometer

Correct answer: c) AC Voltmeter

Explanation: Standard AC voltmeters indicate RMS voltage directly.

MCQ No. 56

Question: The graphical representation used to show the magnitude and phase of alternating quantities is called:

a) Bar graph

b) Vector (Phasor) diagram

c) Pie chart

d) Histogram

Correct answer: b) Vector (Phasor) diagram

Explanation: A phasor diagram represents alternating quantities as rotating vectors, showing both magnitude and phase.

MCQ No. 57

Question: A rotating vector representing an alternating quantity is known as a:

a) Wavefront

b) Phasor

c) Flux line

d) Harmonic

Correct answer: b) Phasor

Explanation: A phasor is a rotating vector used to represent sinusoidal voltages and currents.

MCQ No. 58

Question: In a phasor diagram, the length of the vector represents the:

a) Frequency

b) Magnitude

c) Time period

d) Phase angle

Correct answer: b) Magnitude

Explanation: The length of the phasor corresponds to the amplitude (magnitude) of the alternating quantity.

MCQ No. 59

Question: Instantaneous electrical power in an AC circuit is equal to:

a) $P=VI$

b) $P=v\times i$

c) $P=I^2R$

d) $P=V^2/R$

Correct answer: b) $P=v\times i$

Explanation: Instantaneous power is the product of the instantaneous voltage and instantaneous current at any given instant.

MCQ No. 60

Question: Instantaneous power in an AC circuit:

a) Remains constant

b) Is always zero

c) Varies continuously with time

d) Depends only on resistance

Correct answer: c) Varies continuously with time

Explanation: Since both voltage and current vary continuously with time in an AC circuit, the instantaneous power also changes continuously.

MCQ No. 61

Question: In a purely resistive AC circuit, the current and voltage are:

a) 90° out of phase

b) 180° out of phase

c) In phase

d) Not related

Correct answer: c) In phase

Explanation: In a purely resistive circuit, current and voltage reach their maximum, minimum, and zero values simultaneously. Therefore, there is no phase difference between them.

MCQ No. 62

Question: The phase difference between voltage and current in a purely resistive AC circuit is:

a) 0°

b) 45°

c) 90°

d) 180°

Correct answer: a) 0°

Explanation: Since voltage and current are in phase in a resistor, the phase difference is zero.

MCQ No. 63

Question: The average power consumed in a purely resistive AC circuit is:

a) Zero

b) Maximum

c) Negative

d) Equal to the reactive power

Correct answer: b) Maximum

Explanation: In a resistive circuit, the power factor is 1, so all the supplied electrical power is converted into useful heat energy.

MCQ No. 64

Question: The electrical energy supplied to a pure resistor is mainly converted into:

a) Magnetic energy

b) Heat energy

c) Chemical energy

d) Nuclear energy

Correct answer: b) Heat energy

Explanation: A resistor converts electrical energy into heat due to Joule's heating effect.

MCQ No. 65

Question: Which law is applicable for a purely resistive AC circuit?

a) Faraday's Law

b) Ohm's Law

c) Coulomb's Law

d) Newton's Law

Correct answer: b) Ohm's Law

Explanation: Ohm's law is valid for a purely resistive AC circuit when RMS values are used.

MCQ No. 66

Question: In a purely inductive AC circuit, the current:

a) Leads the voltage by 90°

b) Lags behind the voltage by 90°

c) Is in phase with the voltage

d) Is always zero

Correct answer: b) Lags behind the voltage by 90°

Explanation: Due to self-induced emf, the current in a pure inductor reaches its maximum value one-quarter cycle after the voltage.

MCQ No. 67

Question: The phase difference between voltage and current in a purely inductive circuit is:

a) 0°

b) 45°

c) 90°

d) 180°

Correct answer: c) 90°

Explanation: In a pure inductor, current lags the voltage by 90°.

MCQ No. 68

Question: The opposition offered by an inductor to alternating current is called:

a) Resistance

b) Conductance

c) Inductive reactance

d) Capacitance

Correct answer: c) Inductive reactance

Explanation: Inductive reactance is the opposition offered by an inductor to the flow of AC.

MCQ No. 69

Question: Inductive reactance is represented by the symbol:

a) $X_C$

b) $X_L$

c) $R$

d) $Z$

Correct answer: b) $X_L$

Explanation: The standard symbol for inductive reactance is $X_L$ .

MCQ No. 70

Question: The SI unit of inductive reactance is:

a) Henry

b) Tesla

c) Ohm

d) Farad

Correct answer: c) Ohm

Explanation: Inductive reactance is measured in ohms (Ω), just like resistance.

MCQ No. 71

Question: Which formula gives the inductive reactance?

a) $X_L=\frac{1}{2\pi fC}$

b) $X_L=2\pi fL$

c) $X_L=IR$

d) $X_L=\frac{V}{I^2}$

Correct answer: b) $X_L=2\pi fL$

Explanation: Inductive reactance increases directly with both frequency and inductance.

MCQ No. 72

Question: If the frequency of AC increases, the inductive reactance:

a) Decreases

b) Remains constant

c) Increases

d) Becomes zero

Correct answer: c) Increases

Explanation: Since $X_L=2\pi fL$ , inductive reactance is directly proportional to frequency.

MCQ No. 73

Question: The average power consumed in a purely inductive circuit is:

a) Maximum

b) Equal to the RMS power

c) Zero

d) Infinite

Correct answer: c) Zero

Explanation: In a pure inductor, energy is stored in the magnetic field during one part of the cycle and returned to the source during another. Therefore, the average power consumed over a complete cycle is zero.

MCQ No. 74

Question: Why does a pure inductor consume no average power?

a) Because current is zero

b) Because voltage is zero

c) Because energy stored is returned to the source

d) Because resistance is infinite

Correct answer: c) Because energy stored is returned to the source

Explanation: An ideal inductor stores energy in its magnetic field and releases it back to the source without dissipating it as heat.

MCQ No. 75

Question: A choke coil is primarily used to:

a) Increase current

b) Reduce AC current without much power loss

c) Produce direct current

d) Increase voltage

Correct answer: b) Reduce AC current without much power loss

Explanation: A choke coil has high inductive reactance and very low resistance, allowing it to limit AC current efficiently.

MCQ No. 76

Question: A choke coil mainly works on the principle of:

a) Capacitive reactance

b) Inductive reactance

c) Electrolysis

d) Photoelectric effect

Correct answer: b) Inductive reactance

Explanation: The choke coil limits AC by offering high inductive reactance while wasting very little energy.

MCQ No. 77

Question: In a purely capacitive AC circuit, the current:

a) Lags the voltage by 90°

b) Leads the voltage by 90°

c) Is in phase with the voltage

d) Is always zero

Correct answer: b) Leads the voltage by 90°

Explanation: In a capacitor, the current reaches its maximum value before the voltage, so the current leads the voltage by 90°.

MCQ No. 78

Question: The phase difference in a purely capacitive circuit is:

a) 0°

b) 45°

c) 90°

d) 180°

Correct answer: c) 90°

Explanation: In a purely capacitive circuit, current leads voltage by one-quarter cycle (90°).

MCQ No. 79

Question: The opposition offered by a capacitor to alternating current is called:

a) Resistance

b) Inductive reactance

c) Capacitive reactance

d) Impedance

Correct answer: c) Capacitive reactance

Explanation: Capacitive reactance is the opposition provided by a capacitor to alternating current.

MCQ No. 80

Question: Capacitive reactance is represented by the symbol:

a) $X_C$

b) $X_L$

c) $R$

d) $Z$

Correct answer: a) $X_C$

Explanation: The standard symbol for capacitive reactance is $X_C$ , and its value depends on the capacitance and frequency of the AC supply.

MCQ No. 81

Question: The capacitive reactance of a capacitor is given by:

a) $X_C=2\pi fC$

b) $X_C=\frac{1}{2\pi fC}$

c) $X_C=IR$

d) $X_C=\frac{V}{I}$

Correct answer: b) $X_C=\frac{1}{2\pi fC}$

Explanation: Capacitive reactance is inversely proportional to both frequency and capacitance. As either frequency or capacitance increases, the opposition offered by the capacitor decreases.

MCQ No. 82

Question: If the frequency of an AC source increases, the capacitive reactance:

a) Increases

b) Decreases

c) Remains constant

d) Becomes infinite

Correct answer: b) Decreases

Explanation: Since $X_C=\frac{1}{2\pi fC}$ , increasing the frequency decreases the capacitive reactance.

MCQ No. 83

Question: The average power consumed in a purely capacitive AC circuit is:

a) Maximum

b) Equal to $VI$

c) Zero

d) Infinite

Correct answer: c) Zero

Explanation: An ideal capacitor stores energy in its electric field and returns it to the source. Therefore, no net power is consumed over one complete cycle.

MCQ No. 84

Question: In an RL series circuit, the total opposition to alternating current is called:

a) Resistance

b) Inductive reactance

c) Impedance

d) Conductance

Correct answer: c) Impedance

Explanation: Impedance is the combined effect of resistance and inductive reactance and determines the total opposition to AC.

MCQ No. 85

Question: The symbol used for impedance is:

a) $R$

b) $X_L$

c) $Z$

d) $X_C$

Correct answer: c) $Z$

Explanation: The standard symbol for impedance is $Z$ , and it is measured in ohms (Ω).

MCQ No. 86

Question: The SI unit of impedance is:

a) Henry

b) Farad

c) Ohm

d) Tesla

Correct answer: c) Ohm

Explanation: Like resistance and reactance, impedance is measured in ohms.

MCQ No. 87

Question: In an RC series circuit, the impedance depends upon:

a) Resistance only

b) Capacitive reactance only

c) Both resistance and capacitive reactance

d) Frequency only

Correct answer: c) Both resistance and capacitive reactance

Explanation: The total opposition in an RC circuit results from the combined effect of resistance and capacitive reactance.

MCQ No. 88

Question: An RLC series circuit contains:

a) Only a resistor

b) A resistor and an inductor

c) A resistor, an inductor, and a capacitor

d) Only an inductor

Correct answer: c) A resistor, an inductor, and a capacitor

Explanation: An RLC series circuit consists of all three passive electrical components connected in series.

MCQ No. 89

Question: Resonance in an RLC circuit 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, the inductive and capacitive reactances become equal, making the circuit purely resistive.

MCQ No. 90

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

a) Maximum

b) Equal to resistance only

c) Infinite

d) Zero

Correct answer: b) Equal to resistance only

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

MCQ No. 91

Question: At resonance, the current in a series RLC circuit is:

a) Minimum

b) Zero

c) Maximum

d) Half of the maximum value

Correct answer: c) Maximum

Explanation: At resonance, the impedance is minimum; therefore, the current becomes maximum.

MCQ No. 92

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

a) The color of the coil

b) The sharpness of resonance

c) The supply voltage

d) The frequency of DC

Correct answer: b) The sharpness of resonance

Explanation: A high Q-factor indicates a sharp resonance with better selectivity and lower energy loss.

MCQ No. 93

Question: Metal detectors operate mainly on the principle of:

a) Electrostatic induction

b) Electromagnetic induction

c) Electrolysis

d) Thermoelectric effect

Correct answer: b) Electromagnetic induction

Explanation: A metal detector generates an alternating magnetic field that induces eddy currents in nearby metallic objects, enabling their detection.

MCQ No. 94

Question: Maximum power transfer in an AC circuit occurs when:

a) Resistance is zero

b) Load impedance matches the source impedance

c) Frequency becomes zero

d) Voltage becomes zero

Correct answer: b) Load impedance matches the source impedance

Explanation: According to the maximum power transfer theorem, maximum power is delivered when the load impedance equals the source impedance.

MCQ No. 95

Question: James Clerk Maxwell is best known for:

a) Discovering X-rays

b) Developing the electromagnetic theory

c) Inventing the electric motor

d) Discovering electrons

Correct answer: b) Developing the electromagnetic theory

Explanation: Maxwell unified electricity and magnetism through his famous equations, predicting the existence of electromagnetic waves.

MCQ No. 96

Question: Maxwell predicted that electromagnetic waves travel at:

a) The speed of sound

b) The speed of light

c) Half the speed of light

d) Variable speed

Correct answer: b) The speed of light

Explanation: Maxwell's theory showed that electromagnetic waves propagate through space at the speed of light.

MCQ No. 97

Question: Electromagnetic waves consist of:

a) Electric field only

b) Magnetic field only

c) Oscillating electric and magnetic fields

d) Sound waves

Correct answer: c) Oscillating electric and magnetic fields

Explanation: Electromagnetic waves are formed by mutually perpendicular oscillating electric and magnetic fields that propagate through space.

MCQ No. 98

Question: An Electrocardiogram (ECG) is used to record the electrical activity of the:

a) Brain

b) Heart

c) Lungs

d) Liver

Correct answer: b) Heart

Explanation: An ECG records the electrical impulses generated by the heart during each heartbeat and is widely used to diagnose heart conditions.

MCQ No. 99

Question: The instrument used to obtain an electrocardiogram is called:

a) Oscilloscope

b) Electrocardiograph

c) Ammeter

d) Galvanometer

Correct answer: b) Electrocardiograph

Explanation: An electrocardiograph detects and records the electrical signals produced by the heart, generating an ECG trace.

MCQ No. 100

Question: Which statement best summarizes the significance of alternating current?

a) It can only be produced by batteries.

b) It cannot be transmitted over long distances.

c) It can be transformed efficiently, making it suitable for power transmission and modern electrical systems.

d) It always flows in one direction.

Correct answer: c) It can be transformed efficiently, making it suitable for power transmission and modern electrical systems.

Explanation: Alternating current is the backbone of modern power systems because its voltage can be stepped up for efficient long-distance transmission and stepped down for safe domestic and industrial use. It also forms the basis of transformers, motors, communication systems, and many electronic devices.
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Alternating Current – 100 Basic MCQs with Answers & Explanations | Board & MDCAT Preparation

100 Important Basic MCQs (Level -1) on Alternating Current, Physics (Unit-Wise MCQs Practice):

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

This chapter-wise MCQ collection includes:

This MCQ collection covers:

This question bank helps students to:

Alternating Current MCQs Level 1 – 100 Basic MCQs (1–100)

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MCQ No. 73

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