Name the EM waves used for studying crystal structure of solids. What is itsfrequency range?

X-rays are used for studying crystals structure of solids. Their frequency range from 1016Hz to3 × 1021Hz.
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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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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 velocityC = 1μ0 ε0which is equal to the velocity of light(c = 3 × 108m/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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The oscillating magnetic field in a plane electromagnetic wave is given by
By= (8 × 10-6) sin [2 × 1011t + 300 πx] 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 × 1011t + 300πx]T .

Comparing the given equation with the equation of magnetic field varying sinusoidally with x and t
By = B0 sin2π xλ+2π tT

we get,
2πλ = 300 π

λ = 2300 = 0.0067 m

and B0 = 8 × 10-6T

(i) Wavelength of the electromagnetic wave,λ = 0.0067 m

(ii) Magnitude of electric field is calculated by,

E0 = CB0       = 3 × 108 × 8 × 10-6       

= 24 × 102 = 2400 Vm-1

The requiredexpression for the oscillatingelectric field is,

Ez = E0 sin 2π xλ+2π tT     = 2400 sin (300π x + 2 × 1011 t) V/m.

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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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