EM Waves — CBSE Class 12 board PYQs

The electromagnetic waves used to purify water are

$\vec{E}$ and $\vec{B}$ represent the electric and magnetic fields of an electromagnetic wave respectively. The direction of propagation of the wave is along

Name the electromagnetic radiations used for
(a) water purification, and
(b) eye surgery.

How is the speed of electromagnetic waves in vacuum determined by the electric and magnetic fields of the wave?

Why are microwaves considered suitable for radar systems used in aircraft navigation?

To which part of the electromagnetic spectrum does a wave of frequency $5\times 10^{11}$ Hz belong?

Welders wear special goggles or face masks with glass windows to protect their eyes from certain electromagnetic radiations. Name these radiations and write the range of their frequency.

Name the physical quantity which remains the same for microwaves of wavelength 1 mm and ultraviolet radiation of wavelength $1600\mathring{\text{A}}$ in vacuum.

A plane electromagnetic wave travels in vacuum along the z-direction. What can you say about the directions of the electric and magnetic field vectors?

A plane electromagnetic wave travels in vacuum along the y-direction. What can you say about the directions of the electric and magnetic field vectors?

Which part of the electromagnetic spectrum is used in radar systems?

Name the electromagnetic waves used for studying the crystal structure of solids. What is their frequency range?

Name the electromagnetic radiation to which waves of wavelength of the order of $10^{-2}$ m belong. Give one use of this part of the EM spectrum.

The frequency of oscillation of the electric field vector of a certain electromagnetic wave is $5\times 10^{14}$ Hz. What is the frequency of oscillation of the corresponding magnetic field vector, and to which part of the electromagnetic spectrum does it belong?

Identify the part of the electromagnetic spectrum to which the following wavelengths belong:
(i) 1 mm
(ii) $10^{-11}$ m.

Name the parts of the electromagnetic spectrum which are
(i) stopped by the face mask worn by welders,
(ii) used in the detectors in Earth satellites, and
(iii) used in the 'short-wave band' in communication. Also write the order of wavelengths in each case.

How are infrared waves produced? Why are these waves referred to as heat waves? Give any two uses of infrared waves.

(a) (i) Arrange the following electromagnetic radiations in the ascending order of their frequencies: X-rays, microwaves, gamma rays, radio waves.
(ii) Write two uses of any two of these radiations.

(a) Write the expression for the speed of light in a material medium of relative permittivity ${\epsilon }_r$ and relative magnetic permeability ${\mu }_r$.
(b) Write the wavelength range and name of the electromagnetic waves which are used in (i) radar systems for aircraft navigati …

(a) Identify the part of the electromagnetic spectrum used in (i) radar and (ii) eye surgery. Write their frequency range. (b) Prove that the average energy density of the oscillating electric field is equal to that of the oscillating magnetic field.

(a) Why are infrared waves often called heat waves? Explain.
(b) What do you understand by the statement, "Electromagnetic waves transport momentum"?

How is an electromagnetic wave produced? Draw a sketch of a plane electromagnetic wave propagating along the X-axis, depicting the directions of the oscillating electric and magnetic fields.

How does the Ampere--Maxwell law explain the flow of current through a capacitor when it is being charged by a battery? Write the expression for the displacement current in terms of the rate of change of electric flux.

How are electromagnetic waves produced? What is the source of energy of these waves? Write the mathematical expressions for the electric and magnetic fields of an electromagnetic wave propagating along the z-axis. Write any two important properties of electromagnetic waves.

How are electromagnetic waves produced by oscillating charges? Draw a sketch of a linearly polarized electromagnetic wave propagating in the Z-direction, indicating the directions of the oscillating electric and magnetic fields.

Write Maxwell's generalization of Ampere's circuital law. Show that, in the process of charging a capacitor, the current produced within the plates of the capacitor is $i={\epsilon }_0\frac{d{\Phi }_E}{dt}$, where ${\Phi }_E$ is the electric flux produced during charging of the ca …

Name the parts of the electromagnetic spectrum which are
(a) suitable for radar systems used in aircraft navigation,
(b) used to treat muscular strain, and
(c) used as a diagnostic tool in medicine. Write in brief how each of these waves can be produced.

Considering the case of a parallel plate capacitor being charged, show how one is required to generalize Ampere's circuital law to include the term due to displacement current.

A capacitor made of two parallel plates, each of area A and separation d, is being charged by an external ac source. Show that the displacement current inside the capacitor is the same as the conduction current charging it.

When an ideal capacitor is charged by a dc battery, no current flows through it. However, when an ac source is used, current flows continuously. Explain this on the basis of the concept of displacement current.

A parallel plate capacitor is being charged by a time-varying current. Explain briefly how Ampere's circuital law is generalized to incorporate the effect due to the displacement current.

How does a charge q oscillating at a certain frequency produce electromagnetic waves? Sketch a schematic diagram depicting the electric and magnetic fields for an electromagnetic wave propagating along the Z-direction.

Answer the following questions:
(a) Optical and radio telescopes are built on the ground while X-ray astronomy is possible only from satellites orbiting the Earth. Why?
(b) The small ozone layer on top of the stratosphere is crucial for human survival. Why?

An electromagnetic wave is travelling in a medium with a velocity $\vec{v}=v\hat{i}$. The electric field oscillations of this wave are along the y-axis.
(a) Identify the direction along which the magnetic field oscillations take place.
(b) How are the magnitudes of the electric …

What is meant by the transverse nature of electromagnetic waves? Draw a diagram showing the propagation of an electromagnetic wave along the x-direction, clearly indicating the directions of the oscillating electric and magnetic fields associated with it.

The oscillating electric field of an electromagnetic wave is given by $E_y=30\sin \left(2\times 10^{11}t+300\pi x\right){\text{V m}}^{-1}$.
(a) Obtain the wavelength of the electromagnetic wave.
(b) Write down the expression for the oscillating magnetic field.

Write any four characteristics of electromagnetic waves. Give two uses each of
(i) radio waves and
(ii) microwaves.

Draw a labelled diagram of Hertz's experimental set-up used to produce electromagnetic waves. Explain the generation of electromagnetic waves using this set-up.

Write the order of frequency range and one use of each of the following electromagnetic radiations:
(i) Microwaves
(ii) Ultra-violet rays
(iii) Gamma rays.

Name the constituent radiation of the electromagnetic spectrum which
(a) is used in satellite communication,
(b) is used for studying crystal structure,
(c) is similar to the radiations emitted during decay of radioactive nuclei,
(d) has its wavelength range between 390 nm and 77 …