What is angle of polarisation and obtain the equation for angle of polarisaition.

Explanation

(i) The angle of incidence at which the reflected beam is plane polarised is called polarising angle in`i_p`

(ii) The angle of incidence at which a beam of unpolarised light falling on a transparent surface is reflected as a beam of plane polarised light is called polarising angle or Brewster's angle. It is denoted by `i_p`
(iii) The incidence of polarising angle, the reflected and transmitted rays are perpendicular to each other.
(iv) Suppose, `i_p` is the polarising angle and `r_p` is the corresponding angle of refraction. Then from Figure.
` i_p + 90^@ + r_p = 180^@ " " .....(1)`
`r_p + 90^@ - i_p " " ...(2)`
(v) From Snell's law, the refractive index of the transparent medium is,
` (sin i_p)/(sin r_p) = n " " ....(3)`
(vi) Where n is the refractive index of the medium with respect to air.
(vii) Substituting the value of r, from Equation (2)
`(sin i_p)/(sin (90^@ - i_p)) = (sin I_p)/(cos i_p) = n`
` tan i_p = n `