Brewster’s law : The tangent of the polarizing angle is equal to the refractive index of the reflecting medium with respect to the surrounding (1n2 ). If θB is the polarizing angle,
Here n1 is the absolute refractive index of the surrounding and n2 is that of the reflecting medium.
The angle θB is called the Brewster angle.
Consider a ray of unpolarized monochromatic light incident at an angle θB on a boundary between two transparent media as shown in below figure. Medium 1 is a rarer medium with refractive index n1 and medium 2 is a denser medium with refractive index n2 . Part of incident light gets refracted and the rest
gets reflected. The degree of polarization of the reflected ray varies with the angle of incidence.
The electric field of the incident wave is in the plane perpendicular to the direction of propagation of incident light. This electric field can be resolved into a component parallel to the plane of the paper, shown by double arrows, and a component perpendicular to the plane of the paper shown by dots, both having equal magnitude. Generally, the reflected and refracted rays are partially polarized, i.e., the two components do not have equal magnitude.
In 1812, Sir David Brewster discovered that for a particular angle of incidence. θB , the reflected wave is completely plane-polarized with its electric field perpendicular to the plane of the paper while the refracted wave is partially polarized. This particular angle of incidence (θB ) is called the Brewster angle.
For this angle of incidence, the refracted and reflected rays are perpendicular to each other. For angle of refraction θr ,
