Physics – Electromagnetic Waves
Class 12 Physics (Chapter 8) • 100 Multiple Choice Questions
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Question 1
Who predicted the existence of electromagnetic waves based on his equations?
Correct Answer: James Clerk Maxwell
Question 2
Who experimentally demonstrated the existence of electromagnetic waves for the first time?
Correct Answer: Heinrich Hertz
Question 3
Displacement current is produced by:
Correct Answer: Time-varying electric field
Question 4
What is the formula for displacement current (I_d)?
Correct Answer: I_d = ε₀ (dΦ_E / dt)
Question 5
The speed of electromagnetic waves in vacuum is given by:
Correct Answer: c = 1 / √(μ₀ ε₀)
Question 6
Electromagnetic waves are:
Correct Answer: Transverse waves
Question 7
In an electromagnetic wave, the electric field vector E and magnetic field vector B are:
Correct Answer: Mutually perpendicular and in same phase
Question 8
The ratio of the magnitude of electric field to magnetic field (E / B) in an electromagnetic wave equals:
Correct Answer: Speed of light in vacuum (c)
Question 9
Do electromagnetic waves require a material medium for propagation?
Correct Answer: No, they can propagate through vacuum
Question 10
Which of the following has the maximum wavelength in the electromagnetic spectrum?
Correct Answer: Radio waves
Question 11
Which of the following has the highest frequency in the electromagnetic spectrum?
Correct Answer: Gamma rays
Question 12
Which electromagnetic waves are used in radar systems and microwave ovens?
Correct Answer: Microwaves
Question 13
Which rays are also known as heat waves?
Correct Answer: Infrared rays
Question 14
Which electromagnetic waves are used in medical diagnosis for detecting bone fractures?
Correct Answer: X-rays
Question 15
Which rays are produced by radioactive decay of atomic nuclei?
Correct Answer: Gamma rays
Question 16
Which electromagnetic radiation is responsible for causing skin tanning and is used in water purifiers to kill germs?
Correct Answer: Ultraviolet (UV) rays
Question 17
The energy in an electromagnetic wave is divided equally between:
Correct Answer: Electric field and magnetic field
Question 18
Electromagnetic waves carry:
Correct Answer: Both energy and momentum
Question 19
Pressure exerted by an electromagnetic wave on a surface is called:
Correct Answer: Radiation pressure
Question 20
Which of the following Maxwell's equations represents the non-existence of magnetic monopoles?
Correct Answer: ∮ B · dS = 0 (Gauss's law for magnetism)
Question 21
What is the wavelength range of the visible spectrum of electromagnetic waves?
Correct Answer: 400 nm to 700 nm
Question 22
Which electromagnetic waves are produced by accelerated charges or oscillating electric circuits?
Correct Answer: Radio waves and microwaves
Question 23
Which part of the electromagnetic spectrum is absorbed by the ozone layer in the atmosphere?
Correct Answer: Ultraviolet (UV) radiation
Question 24
The direction of propagation of an electromagnetic wave is given by the direction of vector:
Correct Answer: E × B
Question 25
What is the intensity of an electromagnetic wave related to?
Correct Answer: Square of the amplitude of electric or magnetic field
Question 26
Which of the following electromagnetic waves has the lowest frequency?
Correct Answer: Radio waves
Question 27
Which of the following electromagnetic waves has the shortest wavelength?
Correct Answer: Gamma rays
Question 28
What is the source of infrared waves?
Correct Answer: Hot bodies and molecules
Question 29
What is the source of ultraviolet (UV) radiation?
Correct Answer: Sun and high-voltage arcs
Question 30
Can electromagnetic waves be deflected by electric and magnetic fields?
Correct Answer: No, because they are neutral (carry no net charge)
Question 31
Which scientist first proved mathematically that light is an electromagnetic wave?
Correct Answer: James Clerk Maxwell
Question 32
What is the velocity of electromagnetic waves in a medium of refractive index n and relative permeability μ_r, relative permittivity ε_r?
Correct Answer: v = c / √(μ_r ε_r)
Question 33
Which phenomenon demonstrates the transverse nature of electromagnetic waves?
Correct Answer: Polarization
Question 34
Which of the following waves are used for cellular phone communication?
Correct Answer: Radio waves / Microwaves
Question 35
What is the magnitude of magnetic field B in an EM wave if electric field E has amplitude E₀?
Correct Answer: B₀ = E₀ / c
Question 36
The momentum p of an electromagnetic wave of energy U is given by:
Correct Answer: p = U / c
Question 37
Which of the following waves is used in remote switches of household electronic devices like TVs?
Correct Answer: Infrared waves
Question 38
Which of the following has wavelengths shorter than visible light?
Correct Answer: Ultraviolet rays, X-rays, Gamma rays
Question 39
Ozone layer in the upper atmosphere protects life on Earth by absorbing:
Correct Answer: Harmful UV rays from the Sun
Question 40
The conduction current and displacement current together make total current:
Correct Answer: Continuous across a circuit containing a capacitor
Question 41
Which of the following equations represents Ampere-Maxwell Law?
Correct Answer: ∮ B · dl = μ₀(I + ε₀ dΦ_E / dt)
Question 42
The electric field in an electromagnetic wave is represented as E = E₀ sin(kz - ωt). The magnetic field B can be represented as:
Correct Answer: B = (E₀ / c) sin(kz - ωt)
Question 43
What is the dimensions of the product (μ₀ ε₀)^(-1/2)?
Correct Answer: [L T⁻¹] (Speed)
Question 44
Which waves are used for satellite communication?
Correct Answer: Microwaves
Question 45
Which of the following has wavelengths longer than microwaves?
Correct Answer: Radio waves
Question 46
The average energy density of an electromagnetic wave is given by:
Correct Answer: u = ½ ε₀ E² + ½ (B² / μ₀)
Question 47
Which scientist discovered X-rays?
Correct Answer: Wilhelm Conrad Röntgen
Question 48
Which electromagnetic waves are used for studying crystal structures by diffraction?
Correct Answer: X-rays
Question 49
What is the main characteristic of displacement current in a capacitor charging circuit?
Correct Answer: It equals conduction current in magnitude but exists across the dielectric gap
Question 50
Which of the following components carries electromagnetic energy through space?
Correct Answer: Both oscillating electric and magnetic fields
Question 51
Which electromagnetic waves are used in night vision goggles and security systems?
Correct Answer: Infrared waves
Question 52
What is the frequency range typically associated with radio waves?
Correct Answer: 500 kHz to about 1000 MHz
Question 53
Who discovered infrared waves?
Correct Answer: William Herschel
Question 54
Who discovered ultraviolet rays?
Correct Answer: Johann Ritter
Question 55
What is the phase relationship between electric field E and magnetic field B in an EM wave?
Correct Answer: In phase (they attain maximum and minimum together)
Question 56
Which of the following electromagnetic waves has the longest wavelength?
Correct Answer: Radio waves
Question 57
Which of the following electromagnetic waves has the highest photon energy?
Correct Answer: Gamma rays
Question 58
What is the dimensional formula of electric permittivity of free space (ε₀)?
Correct Answer: [M⁻¹ L⁻³ T⁴ A²]
Question 59
What is the dimensional formula of magnetic permeability of free space (μ₀)?
Correct Answer: [M L T⁻² A⁻²]
Question 60
Which of the following Maxwell equations shows that electric field lines originate from charges?
Correct Answer: Gauss's law for electricity (∮ E · dS = q / ε₀)
Question 61
Which Maxwell equation indicates that a changing magnetic field produces an electric field?
Correct Answer: Faraday's law of electromagnetic induction
Question 62
What is the primary contribution of Maxwell to electromagnetism?
Correct Answer: Introduction of displacement current and unifying electricity, magnetism, and light
Question 63
When an electromagnetic wave travels in a medium, its speed depends on:
Correct Answer: Optical and magnetic properties of the medium (permittivity and permeability)
Question 64
Which of the following waves are used in RADAR for aircraft navigation?
Correct Answer: Microwaves
Question 65
Which waves are used to detect fake currency notes and forged documents?
Correct Answer: Ultraviolet rays
Question 66
Which electromagnetic waves have frequencies just higher than visible light?
Correct Answer: Ultraviolet rays
Question 67
Which electromagnetic waves have frequencies just lower than visible light?
Correct Answer: Infrared rays
Question 68
What is the magnitude of Poynting vector, which represents energy flow per unit area per second in an EM wave?
Correct Answer: S = (1 / μ₀) (E × B)
Question 69
Why can light waves travel through vacuum while sound waves cannot?
Correct Answer: Light waves are electromagnetic and do not require a material medium
Question 70
Which of the following frequency bands is used for FM radio broadcasting?
Correct Answer: 88 MHz to 108 MHz
Question 71
What is the main cause of greenhouse effect on Earth involving electromagnetic waves?
Correct Answer: Absorption and trapping of infrared radiation by atmospheric gases
Question 72
What is the wavelength range of microwaves?
Correct Answer: 0.1 m to 1 mm
Question 73
What is the wavelength range of X-rays?
Correct Answer: 1 nm to 10⁻³ nm (10⁻⁸ m to 10⁻¹³ m)
Question 74
Which of the following quantities oscillates in phase in an electromagnetic wave?
Correct Answer: Electric field E and magnetic field B
Question 75
In Hertz's experimental setup, high voltage sparks across the metal electrodes produced:
Correct Answer: High-frequency electromagnetic waves
Question 76
What happens to the momentum of an electromagnetic wave when it is completely absorbed by a surface?
Correct Answer: Transferred entirely to the surface (p = U/c)
Question 77
What happens to the momentum of an electromagnetic wave when it is completely reflected normally by a surface?
Correct Answer: Momentum transferred is doubled (p = 2U/c)
Question 78
Which of the following has the shortest wavelength among optical and near-optical regions?
Correct Answer: Violet light
Question 79
Which of the following has the longest wavelength in the visible spectrum?
Correct Answer: Red light
Question 80
What is the dimensional formula of intensity of an electromagnetic wave?
Correct Answer: [M L⁰ T⁻³]
Question 81
Which component of sunlight causes a sunburn sensation on human skin?
Correct Answer: Ultraviolet (UV) rays
Question 82
Which of the following electromagnetic waves is produced by high-energy transitions in atomic inner shells?
Correct Answer: X-rays
Question 83
What is the refractive index of a medium in terms of relative permeability (μ_r) and relative permittivity (ε_r)?
Correct Answer: n = √(μ_r ε_r)
Question 84
Which of the following electromagnetic waves is used in radar for speed gun detection of vehicles?
Correct Answer: Microwaves
Question 85
What is the nature of electric and magnetic fields in an electromagnetic wave with respect to the direction of propagation?
Correct Answer: Both are transverse (perpendicular to propagation)
Question 86
Which Indian physicist made significant contributions to the research of microwaves and millimetric waves around 1895?
Correct Answer: Jagadish Chandra Bose
Question 87
What is the magnitude of magnetic field B associated with an electric field E in a plane electromagnetic wave?
Correct Answer: B = E / c
Question 88
Which of the following describes the energy density stored in the electric field of an EM wave?
Correct Answer: u_E = ½ ε₀ E²
Question 89
Which of the following describes the energy density stored in the magnetic field of an EM wave?
Correct Answer: u_B = ½ (B² / μ₀)
Question 90
What is the order of wavelength for microwaves?
Correct Answer: 10⁻³ m to 0.1 m
Question 91
What is the order of wavelength for ultraviolet rays?
Correct Answer: 10⁻⁷ m to 10⁻⁹ m (400 nm to 1 nm)
Question 92
Which of the following waves are used for treatment of cancer cells (radiotherapy)?
Correct Answer: Gamma rays and X-rays
Question 93
The oscillating electric and magnetic fields in an electromagnetic wave are in:
Correct Answer: Same phase
Question 94
Which of the following laws was modified by Maxwell by adding displacement current?
Correct Answer: Ampere's Circuital Law
Question 95
What is the momentum of an electromagnetic wave having energy E?
Correct Answer: p = E / c
Question 96
The electric field vector of an EM wave is given along y-axis and propagation along x-axis. The magnetic field vector must be along:
Correct Answer: z-axis
Question 97
Which of the following waves are used in television remote controls?
Correct Answer: Infrared waves
Question 98
What is the source of production of X-rays?
Correct Answer: Bombardment of high-energy electrons on a heavy metal target
Question 99
Which of the following radiations has maximum penetrating power?
Correct Answer: Gamma rays
Question 100
What is the total number of Maxwell's fundamental equations of electromagnetism?
Correct Answer: 4
