﻿ The oscillating magnetic field in a plane electromagnetic wave is given byBy = (8 × 10-6) sin [2 × 1011 t + 300 πx] T(i) Calculate the wavelength of the electromagnetic wave.(ii) Write down the expression for the oscillating electric field.   from Physics Electromagnetic Waves Class 12 CBSE

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Write any four characteristics of electromagnetic waves. Give two uses of (i) radio-waves (ii) Microwaves.

Characteristics of electromagnetic waves:

(i) Electromagnetic waves are produced by accelerating or oscillating charge.
(ii) E.M. waves do not require any material medium for their propagation.
(iii) E.M. waves travel in free space with a velocity  which is equal to the velocity of light (c = 3 × 108 m/s).
(iv) E.M. waves are transverse in nature.

(i) They are used in radio and TV communication systems.
(ii) Cellular phones use radio waves to transmit voice communication in the ultrahigh frequency (UHF) band.

Uses of Microwaves:

(ii) Microwave ovens are used for cooking purposes.

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The velocity of light in vacuum can be changed by changing
• frequency
• amplitude
• wavelength
• None of these

D.

None of these
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# The oscillating magnetic field in a plane electromagnetic wave is given byBy = (8 × 10-6) sin [2 × 1011 t + 300 $\mathrm{\pi }$x] T(i) Calculate the wavelength of the electromagnetic wave.(ii) Write down the expression for the oscillating electric field.

Given equation for oscillating magnetic field is,
By = (8 × 10-6) sin [2 × 1011 t + 300 $\mathrm{\pi }$x]T .

Comparing the given equation with the equation of magnetic field varying sinusoidally with x and t

we get,

$\therefore$

and

(i) Wavelength of the electromagnetic wave,

(ii) Magnitude of electric field is calculated by,

$\therefore$ The required
expression for the oscillating electric field is,

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The frequencies of X-rays, Y-rays and ultra violet rays are respectively a, b and c. Then
• a < b, b > c
• a > b, b > c
• a > b, b < c
• a < b, b < c

A.

a < b, b > c
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Distinguish between sky wave and space wave propagation. Give a brief description with the help of suitable diagrams indicating how these waves are propagated.

Sky waves. A radio wave transmitted towards the sky and reflected by the ionosphere towards the desired location of the earth is called a sky wave.
Space waves. A radio wave that travels directly from a high transmitting antenna to the receiving station is called space wave.
Diagram. Various propagation modes of electromagnetic waves (EMW) is shown below.

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