Which of the following is also referred to as 'heat waves' ?
(A) Gamma rays
(B) X-rays
(C) UV rays
(D) Infrared rays
CBSE CLASS 12 • PHYSICS • CHAPTER 08
Electromagnetic Waves
73 distinct questions across 98 board paper set appearances (2022–2026).
If $\nu_{\text{X}}$, $\nu_{\text{G}}$ and $\nu_{\text{U}}$ are frequencies of X-rays, Gamma-rays and UV rays respectively, then :
(A) $\nu_{\text{X}} > \nu_{\text{G}} > \nu_{\text{U}}$
(B) $\nu_{\text{G}} > \nu_{\text{X}} > \nu_{\text{U}}$
(C) $\nu_{\text{U}} > \nu_{\text{X}} > \nu_{\text{G}}$
(D) $...
(a) State any three characteristics of electromagnetic waves.
(b) Briefly explain how and where the displacement current exists during the charging of a capacitor.
Which of the following electromagnetic waves has photons of largest momentum ?
(A) X-rays
(B) AM radio waves
(C) Microwaves
(D) TV waves
Name the electromagnetic wave used (i) in radar, (ii) in eye surgery and (iii) as diagnostic tool in medicine. Write their wavelength range also.
Assertion (A) : EM waves do not require a medium for their propagation.
Reason (R) : EM waves are transverse waves.
(a) “The wavelength of the electromagnetic wave is often correlated with the characteristic size of the system that radiates.” Give two examples to justify this statement.
(b) (i) Long distance radio broadcasts use short-wave bands. Why ?
(ii) Optical and radio telescopes are built on the ground, bu...
Assertion (A) : Out of Infrared and radio waves, the radio waves show more diffraction effect.
Reason (R) : Radio waves have greater frequency than infrared waves.
(a) On what factors does the speed of an electromagnetic wave in a medium depend? (b) How is an electromagnetic wave produced? (c) Sketch a schematic diagram depicting the electric and magnetic fields for an electromagnetic wave propagating along z-axis.
The electromagnetic waves used to purify water are
(A) Infrared rays
(B) Ultraviolet rays
(C) X-rays
(D) Gamma rays
(a) (i) Depict a plane electromagnetic wave propagating along the x-axis. Write the expressions for its oscillating electric and magnetic fields. (ii) Write three characteristics of electromagnetic waves. OR (b) Name the electromagnetic waves which are produced by the following : (i) Radioactive dec...
Explain the following, giving proper reason : (a) During charging of a capacitor, displacement current exists in the capacitor. But there is no displacement current when it gets fully charged. (b) The frequency of microwaves in ovens matches with the resonant frequency of water molecules. (c) Infrar...
(a) Name the parts of the electromagnetic spectrum which are (i) also known as 'heat waves' and (ii) absorbed by ozone layer in the atmosphere.
(b) Write briefly one method each, of the production and detection of these radiations.
(a) (i) Long distance radio broadcasts use short-wave bands. Why? (ii) The experimental demonstration of electromagnetic waves is possible only in the low frequency region (the radio wave region). Explain. OR (b) (i) Draw a diagram showing a linearly polarized electromagnetic wave, propagating in th...
Electromagnetic waves used in a diagnostic tool in medicine have a wavelength range
(A) $1\text{ nm to } 10^{-3}\text{ nm}$
(B) $400\text{ nm to } 1\text{ nm}$
(C) $1\text{ mm to } 700\text{ nm}$
(D) $0.1\text{ m to } 1\text{ mm}$
Electromagnetic waves used for purification of water are
(A) X-rays
(B) Ultraviolet rays
(C) Infrared rays
(D) Ultrasonic rays
Welders wear special glass goggles or face masks with glass windows to protect their eyes from
(A) Infrared rays
(B) Ultraviolet rays
(C) X-rays
(D) Microwaves
The phenomenon of interference is shown by
(A) longitudinal mechanical wave only
(B) transverse mechanical wave only
(C) electromagnetic waves only
(D) all these waves
Name the electromagnetic waves which are used for
(i) detection of fractures in bones
(ii) physiotherapy
(iii) radar systems
Also write their wavelength range.
Name the electromagnetic waves which are used
(i) as a diagnostic tool in medicine
(ii) in remote switches for TV sets
(iii) in water purifiers
Also write their wavelength range.
Name the electromagnetic waves which are (i) also known as 'heat waves', (ii) used in LASIK eye surgery, (iii) used to destroy cancer cells. Also write their wavelength range.
Choose the correct statement :
(A) Visible light has higher frequencies and shorter wavelengths than that of X-rays.
(B) Visible light has lower frequencies and shorter wavelengths than that of X-rays.
(C) Visible light has higher frequencies and longer wavelengths than that of X-rays.
(D) Visible ...
Assertion (A) : The ultraviolet light is replaced by X-rays in a photoelectric experiment. The kinetic energy of the emitted electrons decreases.
Reason (R) : Frequency of X-rays is less than that of ultraviolet light.
(a) Only an accelerated charge can produce an electromagnetic wave. Explain. (b) What is the difference between conduction current and displacement current ?
Assertion (A) : Displacement current does not have the same physical effect as the conduction current. Reason (R) : The concept of displacement current is introduced only to satisfy Kirchhoff's rules.
(a) A sinusoidal electromagnetic wave of frequency $40 \text{ MHz}$ travels in free space in the $x$-direction. Calculate the wavelength and time period of the wave.
(b) At some point and at some instant the electric field in the above electromagnetic wave has its maximum value of $750 \text{ N/C}$ ...
What are infrared waves? Why are these waves referred to as 'heat waves'? Give any two uses of these waves.
What are microwaves ? How are they produced ? Give any two uses of microwaves.
What are X-rays ? How are they produced ? Give two uses of X-rays.
Differentiate between conduction current and displacement current. A capacitor is connected across a source providing time-dependent current. Explain how the total current at an instant is the sum of conduction current and displacement current in the circuit at that instant.
Which of the following statement is true for the radio waves and the gamma rays?
(A) The energy of gamma rays is lesser than that of the radio waves.
(B) The frequency of the radio waves is higher than that of gamma rays.
(C) The radio waves and the gamma rays have the same energy.
(D) The energy o...
In free space, which of the following quantities is always larger for X-rays than for a radio wave ?
(A) Speed
(B) Frequency
(C) Amplitude
(D) Wavelength
How are electromagnetic waves produced ? Write any two characteristics of electromagnetic waves. Give one use each of :
(a) radio waves
(b) microwaves.
The amplitude of electric field in an electromagnetic wave in free space is $1000\text{ Vm}^{-1}$. The amplitude of the magnetic field in this electromagnetic wave is :
(A) $3.0 \times 10^{-3}\text{ T}$
(B) $3.33 \times 10^{-8}\text{ T}$
(C) $3.0 \times 10^{11}\text{ T}$
(D) $3.33 \times 10^{-6}\tex...
Assertion (A) : X-rays are produced when slow moving electrons are stopped by a metal target of high atomic number.
Reason (R) : X-rays consist of low-energy photons.
Assertion (A) : X-rays are produced when slow moving electrons are stopped by a metal target of high atomic number.\nReason (R) : X-rays consist of low-energy photons.
Questions number 13 to 16 are Assertion (A) and Reason (R) type questions. Two statements are given — one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.
(A) Both Assertion (A) and Reason (R) are true and Reason...
(a) Differentiate between 'conduction current' and 'displacement current', giving one similarity and one dissimilarity between them.
(b) Explain the existence of electromagnetic waves in free space, using the concept of displacement current.
(a) How are electromagnetic waves produced ?
(b) Write the wavelength range and one use of :
(i) Microwaves, and
(ii) Ultraviolet waves.
Electromagnetic radiation used to kill germs in water purifiers is :
(A) Microwaves
(B) Ultraviolet rays
(C) Gamma rays
(D) Radio waves
Welders wear special glass goggles or face masks with glass windows to protect their eyes from :
(A) UV rays
(B) X-rays
(C) IR rays
(D) Gamma rays
Which of the following electromagnetic waves are known as 'heat waves' ?
(A) UV rays
(B) IR rays
(C) X-rays
(D) Gamma rays
In the four regions, I, II, III and IV, the electric fields are described as :
Region I : $E_x = E_0 \sin $kz - \omega t$$
Region II : $E_x = E_0$
Region III : $E_x = E_0 \sin kz$
Region IV : $E_x = E_0 \cos kz$
The displacement current will exist in the region :
(A) I
(B) IV
(C) II
(D) III
The given diagram exhibits the relationship between the wavelength of the electromagnetic waves and the energy of photon associated with them. The three points P, Q and R marked on the diagram may correspond respectively to :
(A) X-rays, microwaves, UV radiation
(B) X-rays, UV radiation, microwaves
...
Which one of the following correctly represents the change in wave characteristics (all in vacuum) from microwaves to X-rays in electromagnetic spectrum ?
Speed Wavelength Frequency
(A) Remains same Decreases Remains same
(B) Remains same Decreases Increases
(C) Increases Increases Decreases
(D) R...
X-rays are more harmful to human beings than ultraviolet radiations because X-rays -
(A) have frequency lower than that of ultraviolet radiations.
(B) have wavelength smaller than that of ultraviolet radiations.
(C) move faster than ultraviolet radiations in air.
(D) are mechanical waves but ultravi...
(a) The electric field $\vec{\text{E}}$ of an electromagnetic wave propagating in north direction is oscillating in up and down direction. Describe the direction of magnetic field $\vec{\text{B}}$ of the wave.
(b) Are the wave length of radio waves and microwaves longer or shorter than those detecta...
(a) How is an electromagnetic wave produced?
(b) An electromagnetic wave is travelling in vertically upward direction. At an instant, its electric field vector points in west direction. In which direction does the magnetic field vector point at that instant?
(c) Estimate the ratio of shortest wave l...
The electromagnetic radiation used to kill germs in water purifiers is
(A) Ultraviolet rays
(B) Infrared waves
(C) Visible rays
(D) $\gamma$-rays
(a) Write two characteristics of electromagnetic waves.
(b) What is meant by 'displacement current'? Explain briefly how is displacement current set up during charging of a capacitor in a circuit.
The first scientist who produced and observed electromagnetic waves of wavelengths in the range 25 mm - 5 mm was : (A) J.C. Maxwell (B) H.R. Hertz (C) J.C. Bose (D) G. Marconi
Electromagnetic waves with wavelength $10\text{ nm}$ are called :
(A) Infrared waves
(B) Ultraviolet rays
(C) Gamma rays
(D) X-rays
Welders wear special glass goggles or face masks with glass windows to protect their eyes from radiations produced by welding arcs. These radiations are:
(A) X-rays
(B) Ultraviolet rays
(C) Infrared waves
(D) Gamma rays
The speed of electromagnetic waves in a medium depends upon :
(A) properties of the medium
(B) frequency of the waves
(C) wavelength of the waves
(D) intensity of the waves
Which one of the following has the highest frequency ?
(A) Infrared rays
(B) Gamma rays
(C) Radio waves
(D) Microwaves
Electromagnetic waves with frequency $1.0 \times 10^{18}$ Hz are known as :
(A) Infrared rays
(B) Ultraviolet rays
(C) X-rays
(D) Gamma rays
Name the electromagnetic waves with their wavelength range which are used for (i) FM radio broadcast (ii) detection of fracture in bones (iii) treatment of muscular strain
Explain the following giving reasons : (i) ‘Electromagnetic waves differ considerably in their mode of interaction with matter’. (ii) ‘Food items to be heated in microwave oven must contain water’. (iii) ‘Welders wear face mask with glasses during welding’.
Name the part of the electromagnetic spectrum which are
(i) stopped by face mask worn by welders.
(ii) used in detectors in Earth satellites.
(iii) used in ‘short-wave band’ in communication.
Also write the order of wavelengths, in each case.
The frequencies of ultraviolet rays, gamma-rays and microwaves are $\nu_1$, $\nu_2$ and $\nu_3$ respectively. Then :
(A) $\nu_1 = \nu_2 = \nu_3$
(B) $\nu_1 > \nu_2 > \nu_3$
(C) $\nu_2 > \nu_1 > \nu_3$
(D) $\nu_3 > \nu_2 > \nu_1$
What is meant by ‘displacement current’ ? Show that during charging of a capacitor, displacement current is equal to conduction current in the circuit.
Identify the part of the electromagnetic spectrum which:
a) produces heating effect,
b) is absorbed by the ozone layer in the atmosphere,
c) is used for studying crystal structure.
Write any one method of the production of each of the above radiations.
(a) What is meant by displacement current ? Explain. Give an example where such current exists.\nOR\n(b) Write the wavelength range of infrared waves. Why are these waves often called 'heat waves' ? Explain.
Which of the following physical quantities remain the same for X-ray, red light and radio waves when travelling through a medium ?
(a) Wavelength
(b) Speed
(c) Frequency
(d) Momentum
Which of the following radiations has the highest frequency ? (a) Visible light (b) Infrared rays (c) Microwaves (d) X-rays
(a) Identify the part of electromagnetic spectrum which is :
(i) suitable for radar systems.
(ii) sometimes referred to as ‘heat waves’.
Write their wavelength range.
OR
(b) Write two characteristics of electromagnetic waves.
Name the radiation used to kill germs in water purifiers.
Write the range ...
Electromagnetic waves with wavelength
(i) $\lambda_1$ is suitable for radar systems used in aircraft navigation.
(ii) $\lambda_2$ is used to kill germs in water purifiers.
(iii) $\lambda_3$ is used to improve visibility in runways during fog and mist conditions.
Identify and name the part of the ele...
(i) Arrange the following electromagnetic radiation in the ascending order of their frequencies : X-rays, microwaves, gamma rays, radio waves. (ii) Write two uses of any two of these radiation.
(ii) The experimental demonstration of electromagnetic waves is possible only in the low frequency region (the radio wave region). Explain.
(b) (i) Draw a diagram showing a linearly polarized electromagnetic wave, propagating in the z-direction depicting $\vec{E}$ and $\vec{B}$.
(ii) The wavelength of an electromagnetic wave is $10^{-10}\text{ m}$. Identify the wave and mention its one use.
A hydrogen atom has only one electron yet its spectrum has many lines. Explain. Name the spectral series which lies in the visible region of electromagnetic spectrum. Mention the conditions under which the spectral line in this series will have (a) maximum, and (b) minimum wavelengths.
(a) Name the electromagnetic waves which are
(i) produced during decay of a nucleus,
(ii) also known as heat waves,
(iii) absorbed by ozone layer in the atmosphere.
Write one use each of these electromagnetic waves.
OR
(b) [The question text for the OR part is not explicitly provided on this page, o...