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CBSE Gujarat Board Haryana Board

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Class 10 Class 12

Electromagnetic Waves

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 < b, b > c

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The velocity of light in vacuum can be changed by changing

frequency
amplitude
wavelength
None of these

None of these

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The oscillating magnetic field in a plane electromagnetic wave is given by
B_y = (8 × 10^-6) sin [2 × 10¹¹ t + 300 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,
B_y = (8 × 10^-6) sin [2 × 10¹¹ t + 300

π

x]T .

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

B_{y} = B_{0} \sin (\frac{2 π x}{λ} + \frac{2 π t}{T})

we get,

\frac{2 π}{λ} = 300 π

∴

λ = \frac{2}{300} = 0.0067 m

and

B_{0} = 8 \times 10^{- 6} T

(i) Wavelength of the electromagnetic wave,

λ = 0.0067 m

(ii) Magnitude of electric field is calculated by,

E_{0} = {CB}_{0} = 3 \times 10^{8} \times 8 \times 10^{- 6}

= 24 \times 10^{2} = 2400 {Vm}^{- 1}

∴

The required expression for the oscillating electric field is,

E_{z} = E_{0} \sin (\frac{2 π x}{λ} + \frac{2 π t}{T}) = 2400 \sin (300 π x + 2 \times 10^{11} t) V / m .

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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.
Sky waves. A radio wave transmitted towards the sky and reflected by

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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 $C = \frac{1}{\sqrt{μ_{0} ε_{0}}}$ which is equal to the velocity of light (c = 3 × 10⁸ m/s).
(iv) E.M. waves are transverse in nature.

Uses of Radio waves:

(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:

(i) Microwaves are used in Radar systems for aircraft navigation.
(ii) Microwave ovens are used for cooking purposes.

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Electromagnetic Waves

The oscillating magnetic field in a plane electromagnetic wave is given by
B_y = (8 × 10^-6) sin [2 × 10¹¹ t + 300 x] T
(i) Calculate the wavelength of the electromagnetic wave.
(ii) Write down the expression for the oscillating electric field.

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Electromagnetic Waves

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

The oscillating magnetic field in a plane electromagnetic wave is given by
B_y = (8 × 10^-6) sin [2 × 10¹¹ t + 300 x] T
(i) Calculate the wavelength of the electromagnetic wave.
(ii) Write down the expression for the oscillating electric field.