What is Brewster's angle ? Derive relation between Brewster angle and refractive index of medium which produces Plane Polarised light.

Explanation

Brewster.s angle (or polarising angle) is the angle of incidence `.i_(p).` at a plane surface so that reflected light is completely plane polarised.

When light is incident at the polarising angle `i_(p)`, the reflected and refracted rays make a right angle with each other i.e., `angle r=angle(90^(@)-i_(p))`. Therefore, as per Snell.s law, we have
`n=(sini_(p))/(sin r)=(sin i_(p))/(sin (90^(@)-i_(v)))=(sin i_(p))/(cosi_(p))=tani_(p)`