When an unpolarised light is incident on a transparent refracting medium, at a particular angle of incidence the reflected light and refracted light are perpendicular to each other that angle of incident is known as polarising angle.
Since,
Polarisation of reflection, the reflected light gets completely plane polarised and which makes angle \(frac{pi }{2}\) with the refracting light.
According to brewster’s law,
ip + r = 90°
r – is angle of refraction
ip – is polarising angle
r = 90° – ip
by snell’s law
μ1 sin i = μ2 sin r
μ1 = 1 and μ2 = μ
\(frac{sin i}{sin }=mu\)Where
i = ip and
r = 90° – ip
\(frac{sin {{i}_{p}}}{sin (90{}^circ -{{i}_{p}})}=mu\) \(frac{sin {{i}_{p}}}{cos {{i}_{p}}}=mu\) \(tan {{i}_{p}}=mu\) This relation is known as Brewster angle.