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Huygen ’ s Wave Theory
Light travel in a medium in the form of wavefront .
A wavefront is the locus of all the particles vibrating in same phase . All particles on a wavefront behaves as a secondary source of light , which emits secondary wavelets .
The envelope of secondary wavelets represents the new position of a wavefront . When source of light is a point source , the wavefront is spherical .
Amplitude ( A ) is inversely proportional to distance ( x ) i . g ., A ∝ 1 / x .
∴ Intensity ( I ) ∝ ( Amplitude ) 2
When Source of light is linear , the wave front is cylindrical .
Amplitude ( A ) ∝ 1 / √x
∴ Intensity ∝ ( Amplitude ) 2 ∝ 1 / x
Huygen ’ s Principle
( i ) Every point on given wavefront ( called primary wavefront ) acts as a fresh source of new disturbance called secondary wavelets .
( ii ) The secondary wavelets travels in all the directions with the speed of light in the medium .
( iii ) A surface touching these secondary wavelets tangentially in the forward direction at any instant gives the new ( secondary ) wave front of that instant .
Maxwell ’ s Electromagnetic Wave Theory
( i ) Light waves are electromagnetic waves which do not require a material medium for their propagation .
( ii ) Due to transverse nature , light wave undergo polarisation . ( iii ) The velocity of electromagnetic wave in vacuum is c = 1 / √μ o ε o ( iv ) The velocity of electromagnetic waves in medium is less than that of light , v < c v = 1 / √μ o ε o ε r μ r = c / √μ o ε r
( v ) The velocity of electromagnetic waves in a medium depend upon the electric and magnetic properties of the medium .