(a) Define wevefront. Use Huygens 'principle to verify the laws of refraction .
(b) How is linearly polarised light obtained by the process of scattering of light ? Find the
Brawster angle for air- glass interface, when the refractive index of glass = 1.5

Explanation

(i) Wavefront : The continuous locus of all the
particles of a medium, which are vibrating
in the same phase is called a wave front.
(ii) snell's law of refraction : Let PP' represent
the surface separating medium 1 and
medium 2 as shown in fig.

Let `v_(1) and v _(2)` represents the speed of light in
medium 1 and medium 2 respectively . We
assume a plane wevefront AB propagating in
the direcation A'A incident on the interface at m
angle i. Let t be the time by the wevefront to traval the distance BC.
`therefore BC = V_(1) t` [distance = speed `xx` time ]
In order to determine the shape of the refracted wevefront, we draw a sphere of radius `V_(2)t`
from the point A in the second medium (the speed of the weve in second medium is `V_(2)` )
Let CE represent a tangent plane drawn from the point C. Then,
`therefore CE` would represent the refracted wevefront.
In `Delta ABC and Delta AEC`, we have
`sin i = (BC)/(AC)= (V_(1) t)/(AC) and sin r = (AE)/(AC) = (V_(2)i)/(AC)`
Where i and r are the angles of incident and refraction respectively.
`therefore (sin i)/(sin r) = (V_(1)t)/(AC) .(AC)/(V_(2)t)`
`(sin i)/(sin r) = (V_(1))/(V_(2))`
If C reprsents the speed of light in vacuum, then,
`n_(1) = (C)/(V_(1)) and n_(2) = (C)/(V_(2))`
`rArr V_(1) = (C)/(V_(1)) and V_(2) = (C)/(V_(2))`
Where `n_(1) and n_(2)` are the refractive indices of medium 1 and medium 2.
`therefore V_(1) = (C)/(n_(1)) and V_(2) = (C)/(n_(2))`
This is the Snell's law of refraction.
(b) If an incidnet polarized weve falls on an atom it makes the
electrons, oscillate along the randon direction of electric field in the
atom .If light ciewed along perpendicular direction the light is
partially polarised .Only one direction is allowed in this process.
Relation of refracting index and Brewster 's angle is given by
`mu tan i _(p) ` is Brewster's angle.
`therefore i_(p) = tan ^(-1) mu = tan ^(-1) (1.5)`