When the angle of incidence is `60^(@)` on the surface of a glass slab, it is found that the reflected ray is completely polarised. The velocity of light in glass is

Options

A. `sqrt(3) xx 10^(8)` m/s
B. `2xx 10^(8)` m/s
C. `3 xx 10^(8)` m/s
D. `sqrt(2) xx 10^(8)` m/s

Answer

A

Explanation

If the reflected ray is completely plane polarised, then corresponding angle of incidence of `60^(@)` is the polarising angle.
`therefore` By Brewster's law
`n = tan i_(p) = tan 60^(@) = sqrt(3)`
`n = (C )/(V_(g))`
`therefore V_(g) = (C)/(n) = (3xx10^(8))/(sqrt(3))`
` = sqrt(3) xx 10^(8) m//s`