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Question
A beam of unpolarised light is incident on a glass-air interface. Show, using a suitable ray diagram, that light reflected from the interface is totally polarised, when μ = tan iB, where μ is the refractive index of glass with respect to air and iB is the Brewster's angle.
Solution
When unpolarised light is incident on the glass-air interface at Brewster angle iB, then reflected light is totally polarised. This is called Brewster's Law.
When light is incident at Brewster angle, the reflected component OB and the refracted component OC are mutually perpendicular to each other.
From the figure, we have
∠BOY + ∠YOC = 900
( 900 − iB ) + ( 900 − r ) = 900
where, r is angle of refraction
900 − iB = r
According to the Snell's law:
`mu=sini/sinr`
i = iB and r = (900 − iB)
`mu=sini_B/sin(90^@-i_B)=sini_B/cosi_B`
μ =tan iB
Hence proved.
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