Chapter 16: Alternating Current – 100 Basic MCQs (Level 1) with Answers & Explanations

Chapter 16: Alternating Current – 100 Basic MCQs (Level 1) with Answers & Explanations

⚡ Master "Alternating Current" – 100 Basic MCQs with Answers & Explanation ⚡  

Level - 1

Whether you are preparing for annual board examinations, chapter tests, college assessments, or competitive entry tests (MDCAT, ECAT, NUST, PIEAS, GIKI, and other engineering or medical entrance examinations), this comprehensive MCQ collection is designed to help you develop a thorough understanding of Alternating Current (AC). The questions progress systematically from fundamental concepts to advanced numerical problem-solving and higher-order analytical thinking, enabling students to master every aspect of the chapter with confidence and accuracy.

This complete chapter-wise MCQ collection consists of:

  • 100 Basic MCQs – Designed to build a strong conceptual foundation by covering definitions, fundamental principles, and straightforward applications.
  • 100 Advanced & Numerical MCQs – Focused on formula-based calculations, multi-step numerical problems, conceptual reasoning, and examination-oriented applications.
  • 50 Higher-Order Thinking Skills (HOTS) MCQs – Carefully developed to challenge students through analytical reasoning, problem-solving, conceptual integration, and application of multiple physics principles in unfamiliar situations.

This comprehensive MCQ bank thoroughly covers all the learning outcomes of Chapter 16: Alternating Current, including:

  • Nature of alternating current and alternating voltage
  • Time period, frequency, angular frequency, and sinusoidal waveforms
  • Peak, instantaneous, average, and root mean square (RMS) values of alternating current and voltage
  • Mathematical relationships for sinusoidal AC waves
  • Behaviour of alternating current in purely resistive, capacitive, and inductive circuits
  • Phase relationship between current and voltage in R, L, and C circuits
  • Capacitive reactance and inductive reactance, including their dependence on frequency
  • Impedance as the vector combination of resistance and reactance
  • AC Ohm's law and impedance calculations
  • AC power, average power, apparent power, real power, and power factor
  • Numerical applications involving AC circuits and electrical power
  • Resonance in series RLC circuits and factors affecting resonant frequency
  • Practical applications of resonant circuits in communication systems
  • Working principle and applications of metal detectors
  • Three-phase AC supply, its characteristics, advantages, and industrial applications
  • Electromagnetic spectrum, including the properties and applications of different electromagnetic waves
  • Production, transmission, propagation, and reception of electromagnetic waves
  • Practical applications of alternating current and electromagnetic waves in modern technology and everyday life

Each MCQ is presented in a clear, student-friendly format and includes the correct answer along with a concise, concept-based explanation to reinforce understanding and strengthen problem-solving skills.

This carefully structured MCQ collection helps students:

  • Build a solid conceptual understanding of alternating current and AC circuits
  • Master important formulas and their practical applications
  • Develop confidence in solving numerical and analytical problems
  • Understand phase relationships, impedance, resonance, and AC power calculations
  • Strengthen logical reasoning through higher-order conceptual questions
  • Identify and avoid common misconceptions and examination mistakes
  • Improve speed, accuracy, and confidence in solving objective-type questions
  • Prepare effectively for board examinations, chapter tests, quizzes, college assessments, and competitive entrance examinations

With 250 carefully designed MCQs arranged in progressive levels of difficulty—from Basic Level-1 to Advanced & Numerical Level-2 and finally to Higher-Order Thinking Skills (HOTS) Level-3 — this all-in-one question bank provides complete and systematic preparation for Chapter 16: Alternating Current, making it an invaluable resource for students aiming to achieve outstanding academic performance and excel in physics examinations.

Alternating Current MCQs (Set-1: Basic Level

MCQ No. 1

Question: What does AC stand for?

a) Active Current

b) Alternating Current

c) Automatic Current

d) Average Current

Correct answer: b) Alternating Current

Explanation: Alternating Current (AC) is an electric current that changes its direction periodically. It is commonly used in homes, schools, and industries.

MCQ No. 2

Question: Which type of current changes its direction periodically?

a) Direct Current (DC)

b) Alternating Current (AC)

c) Static Current

d) Constant Current

Correct answer: b) Alternating Current (AC)

Explanation: AC continuously reverses its direction after equal intervals of time, whereas DC flows in only one direction.

MCQ No. 3

Question: Which device commonly supplies alternating current to homes?

a) Battery

b) Solar Cell

c) Electric Generator

d) Dry Cell

Correct answer: c) Electric Generator

Explanation: Large electric generators at power stations produce alternating current, which is transmitted to homes and industries.

MCQ No. 4

Question: The graph of an alternating current is generally:

a) Circular

b) Triangular

c) Sinusoidal

d) Rectangular

Correct answer: c) Sinusoidal

Explanation: The voltage and current in an AC circuit usually vary in the form of a smooth sine wave, known as a sinusoidal waveform.

MCQ No. 5

Question: One complete cycle of an AC wave consists of:

a) Only a positive half-cycle

b) Only a negative half-cycle

c) One positive and one negative half-cycle

d) Two positive half-cycles

Correct answer: c) One positive and one negative half-cycle

Explanation: A complete AC cycle includes one positive half-cycle followed by one negative half-cycle.

MCQ No. 6

Question: The time taken to complete one cycle of an AC wave is called:

a) Frequency

b) Wavelength

c) Time Period

d) Amplitude

Correct answer: c) Time Period

Explanation: The time period is the time required for one complete cycle of an alternating current or voltage.

MCQ No. 7

Question: The SI unit of time period is:

a) Hertz

b) Volt

c) Second

d) Ampere

Correct answer: c) Second

Explanation: Time period measures time, so its SI unit is the second (s).

MCQ No. 8

Question: Frequency is defined as the number of complete cycles per:

a) Minute

b) Hour

c) Second

d) Day

Correct answer: c) Second

Explanation: Frequency tells us how many complete cycles occur in one second.

MCQ No. 9

Question: The SI unit of frequency is:

a) Ampere

b) Volt

c) Hertz

d) Ohm

Correct answer: c) Hertz

Explanation: Frequency is measured in hertz (Hz). One hertz means one cycle per second.

MCQ No. 10

Question: If an AC wave completes 50 cycles in one second, its frequency is:

a) 25 Hz

b) 50 Hz

c) 100 Hz

d) 150 Hz

Correct answer: b) 50 Hz

Explanation: Frequency is the number of cycles completed in one second. Therefore, 50 cycles per second means a frequency of 50 Hz.

MCQ No. 11

Question: The relationship between frequency (f) and time period (T) is:

a) f=Tf=T

b) f=T2f=T^2

c) f=1Tf=\frac{1}{T}

d) f=2Tf=2T

Correct answer: c) f=1Tf=\frac{1}{T}

Explanation: Frequency and time period are reciprocals of each other. If one increases, the other decreases.

MCQ No. 12

Question: If the time period of an AC wave increases, its frequency:

a) Increases

b) Decreases

c) Remains the same

d) Becomes zero

Correct answer: b) Decreases

Explanation: Since frequency is the reciprocal of time period, a larger time period means a smaller frequency.

MCQ No. 13

Question: The maximum value reached by an alternating current is called its:

a) Average value

b) RMS value

c) Peak value

d) Minimum value

Correct answer: c) Peak value

Explanation: The peak value is the highest value of current or voltage reached during a cycle.

MCQ No. 14

Question: Another name for the peak value of an AC quantity is:

a) Effective value

b) Maximum value

c) Average value

d) Instantaneous value

Correct answer: b) Maximum value

Explanation: Peak value is also called the maximum value because it represents the greatest value attained by the current or voltage.

MCQ No. 15

Question: The RMS value of an alternating current is also known as its:

a) Lowest value

b) Effective value

c) Peak value

d) Instantaneous value

Correct answer: b) Effective value

Explanation: The RMS (Root Mean Square) value is called the effective value because it produces the same heating effect as an equivalent direct current.

MCQ No. 16

Question: RMS stands for:

a) Root Mean Square

b) Relative Mean Square

c) Random Mean Signal

d) Root Maximum Signal

Correct answer: a) Root Mean Square

Explanation: RMS stands for Root Mean Square. It is the standard method of expressing the effective value of alternating current and voltage.

MCQ No. 17

Question: The RMS value of AC is mainly used because it represents:

a) The highest current

b) The lowest current

c) The effective value of AC

d) The average value over half a cycle

Correct answer: c) The effective value of AC

Explanation: The RMS value gives the equivalent DC value that produces the same amount of heat in a resistor.

MCQ No. 18

Question: Which quantity changes continuously with time in an AC circuit?

a) Only resistance

b) Only voltage

c) Current and voltage

d) Only power

Correct answer: c) Current and voltage

Explanation: In an AC circuit, both current and voltage continuously change in magnitude and reverse direction with time.

MCQ No. 19

Question: The frequency of the 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 the domestic AC supply in Pakistan is 50 Hz, meaning the current completes 50 cycles every second.

MCQ No. 20

Question: During one complete cycle, an alternating current changes its direction:

a) Once

b) Twice

c) Three times

d) It never changes direction

Correct answer: b) Twice

Explanation: During one complete cycle, the current flows first in one direction and then in the opposite direction. Thus, it reverses direction twice, once every half-cycle.

MCQ No. 21

Question: Which of the following quantities describes how rapidly an AC wave oscillates?

a) Resistance

b) Frequency

c) Voltage

d) Power

Correct answer: b) Frequency

Explanation: Frequency indicates how many complete cycles an alternating current or voltage completes in one second. It shows how rapidly the AC wave oscillates.

MCQ No. 22

Question: If the frequency of an AC source increases, its time period will:

a) Increase

b) Decrease

c) Remain unchanged

d) Become zero

Correct answer: b) Decrease

Explanation: Frequency and time period are inversely related. As frequency increases, the time taken to complete one cycle decreases.

MCQ No. 23

Question: Which symbol is commonly used to represent the peak value of alternating current?

a) II

b) ImaxI_{\text{max}}

c) IavgI_{\text{avg}}

d) IrI_{\text{r}}

Correct answer: b) ImaxI_{\text{max}}

Explanation: The symbol ImaxI_{\text{max}} represents the maximum or peak value of alternating current during a cycle.

MCQ No. 24

Question: The peak value of an AC voltage is represented by:

a) VmaxV_{\text{max}}

b) VavgV_{\text{avg}}

c) VdcV_{\text{dc}}

d) VminV_{\text{min}}

Correct answer: a) VmaxV_{\text{max}}

Explanation: VmaxV_{\text{max}} denotes the highest value reached by the alternating voltage during one cycle.

MCQ No. 25

Question: Which value of AC is measured by most household voltmeters?

a) Peak value

b) Instantaneous value

c) RMS value

d) Average value

Correct answer: c) RMS value

Explanation: Household voltmeters are calibrated to measure the RMS (effective) value of alternating voltage.

MCQ No. 26

Question: The RMS value of AC is important because it is equivalent to the DC value producing the same:

a) Brightness only

b) Heating effect

c) Magnetic field only

d) Frequency

Correct answer: b) Heating effect

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

MCQ No. 27

Question: The waveform of an ideal alternating current repeats after every:

a) Half cycle

b) One complete cycle

c) Quarter cycle

d) Two cycles

Correct answer: b) One complete cycle

Explanation: An AC waveform repeats its pattern after one complete cycle, making it a periodic wave.

MCQ No. 28

Question: In an AC circuit containing only a resistor, the current and voltage are:

a) 180° out of phase

b) 90° out of phase

c) In phase

d) Not related

Correct answer: c) In phase

Explanation: In a purely resistive AC circuit, current and voltage reach their maximum and minimum values at the same time. Therefore, they are in phase.

MCQ No. 29

Question: In a purely resistive AC circuit, the phase difference between current and voltage is:

a) 0°

b) 45°

c) 90°

d) 180°

Correct answer: a) 0°

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

MCQ No. 30

Question: Which component opposes the flow of current by its resistance only?

a) Capacitor

b) Inductor

c) Resistor

d) Transformer

Correct answer: c) Resistor

Explanation: A resistor opposes current through its electrical resistance. It does not produce any phase difference between current and voltage.

MCQ No. 31

Question: Which circuit element stores electrical energy in an electric field?

a) Resistor

b) Capacitor

c) Inductor

d) Fuse

Correct answer: b) Capacitor

Explanation: A capacitor stores electrical energy in the electric field formed between its plates.

MCQ No. 32

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

a) Lags behind the voltage

b) Leads the voltage

c) Is equal to zero

d) Is always constant

Correct answer: b) Leads the voltage

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

MCQ No. 33

Question: In a purely capacitive circuit, the phase difference between current and voltage is:

a) 0°

b) 45°

c) 90°

d) 180°

Correct answer: c) 90°

Explanation: In a capacitor, the current leads the voltage by 90°, resulting in a phase difference of 90°.

MCQ No. 34

Question: Which component stores energy in a magnetic field?

a) Capacitor

b) Battery

c) Inductor

d) Resistor

Correct answer: c) Inductor

Explanation: An inductor stores energy in the magnetic field produced around its coil when current flows through it.

MCQ No. 35

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

a) Leads the voltage

b) Lags behind the voltage

c) Is equal to the voltage

d) Does not change

Correct answer: b) Lags behind the voltage

Explanation: In an inductor, the current reaches its maximum value after the voltage. Hence, current lags voltage by 90°.

MCQ No. 36

Question: In a purely inductive circuit, the phase difference between current and voltage is:

a) 0°

b) 30°

c) 90°

d) 180°

Correct answer: c) 90°

Explanation: In a purely inductive AC circuit, the current lags behind the voltage by 90°.

MCQ No. 37

Question: Which quantity opposes the flow of alternating current in a capacitor?

a) Resistance

b) Capacitance

c) Capacitive Reactance

d) Conductance

Correct answer: c) Capacitive Reactance

Explanation: Capacitive reactance is the opposition offered by a capacitor to the flow of alternating current.

MCQ No. 38

Question: The SI unit of capacitive reactance is:

a) Volt

b) Ampere

c) Ohm

d) Farad

Correct answer: c) Ohm

Explanation: Like resistance, capacitive reactance is measured in ohms (Ω).

MCQ No. 39

Question: Which quantity opposes the flow of alternating current in an inductor?

a) Resistance

b) Inductance

c) Inductive Reactance

d) Voltage

Correct answer: c) Inductive Reactance

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

MCQ No. 40

Question: The SI unit of inductive reactance is:

a) Henry

b) Volt

c) Ohm

d) Tesla

Correct answer: c) Ohm

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

MCQ No. 41

Question: Capacitive reactance is represented by the symbol:

a) XLX_L

b) XCX_C

c) RR

d) ZZ

Correct answer: b) XCX_C

Explanation: Capacitive reactance is represented by XCX_C. It is the opposition offered by a capacitor to the flow of alternating current.

MCQ No. 42

Question: Inductive reactance is represented by the symbol:

a) XCX_C

b) R

c) XLX_L

d) ZZ

Correct answer: c) XLX_L

Explanation: Inductive reactance is represented by XLX_L. It is the opposition offered by an inductor to alternating current.

MCQ No. 43

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

a) Reactance

b) Impedance

c) Resistance

d) Inductance

Correct answer: c) Resistance

Explanation: A resistor opposes both AC and DC by its resistance. Unlike capacitors and inductors, it does not produce reactance.

MCQ No. 44

Question: Which quantity combines both resistance and reactance in an AC circuit?

a) Voltage

b) Current

c) Impedance

d) Frequency

Correct answer: c) Impedance

Explanation: Impedance is the total opposition offered to alternating current. It includes both resistance and reactance.

MCQ No. 45

Question: The symbol used for impedance is:

a) XX

b) RR

c) ZZ

d) II

Correct answer: c) ZZ

Explanation: The symbol ZZ represents impedance, which is measured in ohms.

MCQ No. 46

Question: The SI unit of impedance is:

a) Volt

b) Ohm

c) Henry

d) Farad

Correct answer: b) Ohm

Explanation: Impedance is measured in ohms (Ω), the same unit used for resistance and reactance.

MCQ No. 47

Question: Impedance in an AC circuit is found by the vector addition of:

a) Voltage and current

b) Resistance and reactance

c) Frequency and time period

d) Current and power

Correct answer: b) Resistance and reactance

Explanation: Since resistance and reactance act at right angles in a phasor diagram, impedance is obtained by their vector addition.

MCQ No. 48

Question: Which diagram is commonly used to represent impedance in an AC circuit?

a) Bar graph

b) Pie chart

c) Impedance triangle

d) Line graph

Correct answer: c) Impedance triangle

Explanation: The impedance triangle shows the relationship among resistance, reactance, and impedance.

MCQ No. 49

Question: Which of the following is measured in ohms (Ω)?

a) Resistance only

b) Reactance only

c) Impedance only

d) All of these

Correct answer: d) All of these

Explanation: Resistance, reactance, and impedance all oppose the flow of current and are measured in ohms.

MCQ No. 50

Question: Which quantity determines the total opposition to the flow of AC?

a) Current

b) Frequency

c) Impedance

d) Capacitance

Correct answer: c) Impedance

Explanation: Impedance is the combined effect of resistance and reactance, making it the total opposition to alternating current.

MCQ No. 51

Question: Electric power is the rate at which electrical energy is:

a) Stored

b) Generated

c) Transferred or consumed

d) Measured

Correct answer: c) Transferred or consumed

Explanation: Electric power is the rate at which electrical energy is transferred or converted into other forms such as heat or light.

MCQ No. 52

Question: The SI unit of electrical power is:

a) Joule

b) Watt

c) Volt

d) Ampere

Correct answer: b) Watt

Explanation: The SI unit of power is the watt (W). One watt equals one joule of energy transferred per second.

MCQ No. 53

Question: In a purely resistive AC circuit, electrical power is mainly converted into:

a) Heat

b) Magnetic energy

c) Chemical energy

d) Nuclear energy

Correct answer: a) Heat

Explanation: A resistor converts electrical energy into heat due to its resistance. This is known as the heating effect of electric current.

MCQ No. 54

Question: Which value of current is used in AC power calculations?

a) Peak value

b) Instantaneous value

c) RMS value

d) Minimum value

Correct answer: c) RMS value

Explanation: AC power calculations use RMS values because they represent the effective values of current and voltage.

MCQ No. 55

Question: Which value of voltage is used in AC power calculations?

a) Maximum value

b) RMS value

c) Minimum value

d) Average value

Correct answer: b) RMS value

Explanation: RMS voltage is used because it produces the same heating effect as an equivalent DC voltage.

MCQ No. 56

Question: Which circuit condition produces the maximum current?

a) High resistance

b) Resonance

c) Low frequency only

d) High capacitance only

Correct answer: b) Resonance

Explanation: At resonance, the inductive and capacitive reactances become equal, resulting in minimum impedance and maximum current.

MCQ No. 57

Question: Resonance occurs in an AC circuit containing:

a) Only a resistor

b) Only a capacitor

c) Only an inductor

d) An inductor and a capacitor

Correct answer: d) An inductor and a capacitor

Explanation: Resonance occurs in an RLC circuit when the inductive reactance equals the capacitive reactance.

MCQ No. 58

Question: At resonance, the inductive reactance is:

a) Greater than capacitive reactance

b) Less than capacitive reactance

c) Equal to capacitive reactance

d) Equal to resistance

Correct answer: c) Equal to capacitive reactance

Explanation: At resonance, XL=XCX_L = X_C. This condition minimizes impedance and allows maximum current to flow.

MCQ No. 59

Question: Resonant circuits are commonly used in:

a) Water pumps

b) Radio and television receivers

c) Electric heaters

d) Dry cells

Correct answer: b) Radio and television receivers

Explanation: Resonant circuits are used to select a desired frequency from many transmitted signals in radios and televisions.

MCQ No. 60

Question: The main purpose of a resonant circuit is to:

a) Increase resistance

b) Select a particular frequency

c) Produce direct current

d) Reduce voltage to zero

Correct answer: b) Select a particular frequency

Explanation: A resonant circuit is designed to respond strongly to one specific frequency while rejecting others. This property is widely used in communication systems.

MCQ No. 61

Question: A metal detector works on the principle of:

a) Electrolysis

b) Electromagnetic induction

c) Static electricity

d) Photoelectric effect

Correct answer: b) Electromagnetic induction

Explanation: A metal detector uses electromagnetic induction. When a metal object enters the magnetic field produced by the detector, it disturbs the field, allowing the device to detect the object.

MCQ No. 62

Question: Metal detectors are commonly used at:

a) Farms

b) Airports

c) Water tanks

d) Libraries

Correct answer: b) Airports

Explanation: Metal detectors are widely used at airports, shopping malls, railway stations, and other public places to detect hidden metal objects for security purposes.

MCQ No. 63

Question: Which of the following objects can be detected by a metal detector?

a) Plastic bottle

b) Wooden stick

c) Iron key

d) Rubber ball

Correct answer: c) Iron key

Explanation: Metal detectors detect metallic objects such as iron keys, coins, knives, and other metal items.

MCQ No. 64

Question: A three-phase AC supply consists of:

a) One alternating voltage

b) Two alternating voltages

c) Three alternating voltages

d) Four alternating voltages

Correct answer: c) Three alternating voltages

Explanation: A three-phase AC supply consists of three alternating voltages of equal magnitude and frequency that are out of phase with each other.

MCQ No. 65

Question: A three-phase AC supply is mainly used in:

a) Wrist watches

b) Industries

c) Flashlights

d) Mobile chargers only

Correct answer: b) Industries

Explanation: Three-phase AC is commonly used in industries because it provides a more efficient and continuous supply of electrical power.

MCQ No. 66

Question: The main advantage of a three-phase AC supply is:

a) It requires no wires.

b) It provides a smoother and more efficient power supply.

c) It works only with batteries.

d) It produces direct current.

Correct answer: b) It provides a smoother and more efficient power supply.

Explanation: Three-phase AC delivers power more smoothly and efficiently than single-phase AC, making it suitable for heavy electrical loads.

MCQ No. 67

Question: Electromagnetic waves can travel through:

a) Solids only

b) Liquids only

c) Vacuum

d) Water only

Correct answer: c) Vacuum

Explanation: Electromagnetic waves do not require a material medium. They can travel through empty space (vacuum).

MCQ No. 68

Question: Electromagnetic waves travel at approximately:

a) 3×1063 \times 10^6 m/s

b) 3×1073 \times 10^7 m/s

c) 3×1083 \times 10^8 m/s

d) 3×1093 \times 10^9 m/s

Correct answer: c) 3×1083 \times 10^8 m/s

Explanation: All electromagnetic waves travel in a vacuum at the speed of light, which is approximately 3×1083 \times 10^8 m/s.

MCQ No. 69

Question: Which electromagnetic wave has the longest wavelength?

a) Gamma rays

b) X-rays

c) Radio waves

d) Ultraviolet rays

Correct answer: c) Radio waves

Explanation: Radio waves have the longest wavelengths and the lowest frequencies in the electromagnetic spectrum.

MCQ No. 70

Question: Which electromagnetic wave has the shortest wavelength?

a) Infrared rays

b) Radio waves

c) Gamma rays

d) Microwaves

Correct answer: c) Gamma rays

Explanation: Gamma rays have the shortest wavelengths and the highest frequencies in the electromagnetic spectrum.

MCQ No. 71

Question: Which electromagnetic waves are mainly used for radio broadcasting?

a) Infrared rays

b) Radio waves

c) X-rays

d) Ultraviolet rays

Correct answer: b) Radio waves

Explanation: Radio broadcasting uses radio waves because they can travel long distances and carry information effectively.

MCQ No. 72

Question: Which electromagnetic waves are commonly used in microwave ovens?

a) Microwaves

b) Radio waves

c) X-rays

d) Gamma rays

Correct answer: a) Microwaves

Explanation: Microwave ovens use microwaves to heat food by causing water molecules inside the food to vibrate rapidly.

MCQ No. 73

Question: Which electromagnetic waves are mainly responsible for the sensation of heat?

a) X-rays

b) Infrared rays

c) Gamma rays

d) Radio waves

Correct answer: b) Infrared rays

Explanation: Infrared rays are commonly associated with heat. Warm objects emit infrared radiation.

MCQ No. 74

Question: Which part of the electromagnetic spectrum is visible to the human eye?

a) Infrared rays

b) Ultraviolet rays

c) Visible light

d) X-rays

Correct answer: c) Visible light

Explanation: Visible light is the small part of the electromagnetic spectrum that the human eye can detect.

MCQ No. 75

Question: Which electromagnetic waves help the human body produce vitamin D?

a) Radio waves

b) Microwaves

c) Ultraviolet rays

d) Gamma rays

Correct answer: c) Ultraviolet rays

Explanation: Moderate exposure to ultraviolet (UV) rays from sunlight helps the skin produce vitamin D.

MCQ No. 76

Question: Which electromagnetic waves are widely used for medical imaging of bones?

a) Radio waves

b) Infrared rays

c) X-rays

d) Microwaves

Correct answer: c) X-rays

Explanation: X-rays can pass through soft tissues but are absorbed more by bones, making them useful for medical imaging.

MCQ No. 77

Question: Which electromagnetic waves have the highest frequency?

a) Radio waves

b) Infrared rays

c) Gamma rays

d) Microwaves

Correct answer: c) Gamma rays

Explanation: Gamma rays have the highest frequency and the greatest energy among all electromagnetic waves.

MCQ No. 78

Question: Electromagnetic waves are produced by:

a) Stationary electric charges

b) Accelerating electric charges

c) Magnets only

d) Batteries only

Correct answer: b) Accelerating electric charges

Explanation: Electromagnetic waves are produced when electric charges accelerate or vibrate. These changing electric and magnetic fields generate the waves.

MCQ No. 79

Question: Which device is commonly used to transmit electromagnetic waves?

a) Antenna

b) Thermometer

c) Barometer

d) Ammeter

Correct answer: a) Antenna

Explanation: A transmitting antenna converts electrical signals into electromagnetic waves, which then travel through space.

MCQ No. 80

Question: Which device is commonly used to receive electromagnetic waves?

a) Generator

b) Transformer

c) Receiving antenna

d) Voltmeter

Correct answer: c) Receiving antenna

Explanation: A receiving antenna captures electromagnetic waves and converts them into electrical signals for communication devices such as radios and televisions.

MCQ No. 81

Question: Which scientist first predicted the existence of electromagnetic waves?

a) Isaac Newton

b) James Clerk Maxwell

c) Albert Einstein

d) Michael Faraday

Correct answer: b) James Clerk Maxwell

Explanation: James Clerk Maxwell developed the electromagnetic theory and predicted the existence of electromagnetic waves before they were experimentally confirmed.

MCQ No. 82

Question: Which scientist experimentally produced electromagnetic waves for the first time?

a) Nikola Tesla

b) Heinrich Hertz

c) Thomas Edison

d) J. J. Thomson

Correct answer: b) Heinrich Hertz

Explanation: Heinrich Hertz successfully produced and detected electromagnetic waves, confirming Maxwell's theory.

MCQ No. 83

Question: Which property is common to all electromagnetic waves?

a) They require a material medium to travel.

b) They travel at the same speed in a vacuum.

c) They have the same wavelength.

d) They have the same frequency.

Correct answer: b) They travel at the same speed in a vacuum.

Explanation: All electromagnetic waves travel through a vacuum at the speed of light, approximately 3×1083 \times 10^8 m/s.

MCQ No. 84

Question: Which of the following is not an electromagnetic wave?

a) Radio waves

b) Sound waves

c) X-rays

d) Gamma rays

Correct answer: b) Sound waves

Explanation: Sound waves are mechanical waves and require a material medium to travel, whereas electromagnetic waves do not.

MCQ No. 85

Question: Electromagnetic waves consist of:

a) Electric field only

b) Magnetic field only

c) Electric and magnetic fields

d) Gravitational field only

Correct answer: c) Electric and magnetic fields

Explanation: Electromagnetic waves are made up of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation.

MCQ No. 86

Question: Which of the following electromagnetic waves has the lowest frequency?

a) Microwaves

b) Infrared rays

c) Radio waves

d) Ultraviolet rays

Correct answer: c) Radio waves

Explanation: Radio waves have the lowest frequency and the longest wavelength in the electromagnetic spectrum.

MCQ No. 87

Question: Which electromagnetic waves have higher energy than X-rays?

a) Radio waves

b) Infrared rays

c) Gamma rays

d) Microwaves

Correct answer: c) Gamma rays

Explanation: Gamma rays have the highest frequency and energy in the electromagnetic spectrum, making them more energetic than X-rays.

MCQ No. 88

Question: Which electromagnetic waves are commonly used in television and mobile communication?

a) Radio waves and microwaves

b) Infrared rays and X-rays

c) Ultraviolet rays and gamma rays

d) Visible light and X-rays

Correct answer: a) Radio waves and microwaves

Explanation: Radio waves and microwaves are widely used for wireless communication, including television broadcasting, mobile phones, and satellite communication.

MCQ No. 89

Question: The transmission of radio signals mainly depends on:

a) Mechanical waves

b) Electromagnetic waves

c) Water waves

d) Sound waves

Correct answer: b) Electromagnetic waves

Explanation: Radio signals are transmitted through electromagnetic waves, which can travel through the atmosphere and space.

MCQ No. 90

Question: In communication systems, the receiving antenna converts electromagnetic waves into:

a) Heat energy

b) Light energy

c) Electrical signals

d) Chemical energy

Correct answer: c) Electrical signals

Explanation: A receiving antenna captures electromagnetic waves and converts them into electrical signals for processing by electronic devices.

MCQ No. 91

Question: Which of the following quantities is measured in hertz (Hz)?

a) Voltage

b) Frequency

c) Resistance

d) Power

Correct answer: b) Frequency

Explanation: Frequency is measured in hertz (Hz), where 1 Hz = 1 cycle per second.

MCQ No. 92

Question: Which quantity is measured in ohms (Ω)?

a) Frequency

b) Time period

c) Impedance

d) Power

Correct answer: c) Impedance

Explanation: Impedance is the total opposition to alternating current and is measured in ohms (Ω).

MCQ No. 93

Question: Which quantity is measured in watts (W)?

a) Resistance

b) Current

c) Voltage

d) Power

Correct answer: d) Power

Explanation: Power is the rate at which electrical energy is transferred or converted, and its SI unit is the watt (W).

MCQ No. 94

Question: Which instrument is commonly used to measure AC voltage?

a) Ammeter

b) Voltmeter

c) Galvanometer

d) Thermometer

Correct answer: b) Voltmeter

Explanation: A voltmeter is used to measure the potential difference (voltage) across two points in an AC circuit.

MCQ No. 95

Question: Which instrument is used to measure AC current?

a) Voltmeter

b) Ammeter

c) Barometer

d) Hygrometer

Correct answer: b) Ammeter

Explanation: An ammeter is connected in series with a circuit to measure the current flowing through it.

MCQ No. 96

Question: Which of the following is an advantage of alternating current over direct current?

a) It cannot be transmitted over long distances.

b) Its voltage can be changed easily using transformers.

c) It always flows in one direction.

d) It cannot be generated by power stations.

Correct answer: b) Its voltage can be changed easily using transformers.

Explanation: One major advantage of AC is that its voltage can be increased or decreased easily using transformers, making long-distance power transmission more efficient.

MCQ No. 97

Question: Which type of current is supplied to homes in Pakistan?

a) Direct current

b) Alternating current

c) Pulsating current

d) Static current

Correct answer: b) Alternating current

Explanation: Homes in Pakistan receive alternating current (AC), which is supplied at a frequency of 50 Hz.

MCQ No. 98

Question: Which of the following quantities changes direction periodically?

a) Direct current

b) Alternating current

c) Constant current

d) Steady current

Correct answer: b) Alternating current

Explanation: Alternating current reverses its direction at regular intervals, while direct current flows in only one direction.

MCQ No. 99

Question: Alternating current is mainly used because it is:

a) Easier to transmit over long distances

b) Produced only by batteries

c) Unable to change voltage

d) Always stronger than direct current

Correct answer: a) Easier to transmit over long distances

Explanation: AC can be transmitted efficiently over long distances because its voltage can be stepped up and stepped down using transformers, reducing power losses.

MCQ No. 100

Question: Which statement about alternating current is correct?

a) It flows only in one direction.

b) It has zero frequency.

c) It changes both its magnitude and direction with time.

d) It cannot pass through a capacitor.

Correct answer: c) It changes both its magnitude and direction with time.

Explanation: Alternating current continuously changes both its magnitude and direction with time. This periodic variation is the defining characteristic of AC.


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