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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.