Brewster angle states a simple relation between the angle of polarization and the refractive index of the medium. It has been observed experimentally that the reflected and refracted rays are at right angles to each other. when the light is incident at polarizing angle. When a light beam strikes a transparent substance, it can be separated into two light components: orthogonal (S) and parallel (P) components. Brewster discovered that the reflection coefficient of the parallel component goes to zero at a specific angle of incidence β, often known as the Brewster angle. The direction of the transmitted and reflected beams is orthogonal at this angle.

Here m is the refractive index of the medium (glass) Substituting for r, we get,