Polarisation by reflection :
It is found that when a beam of ordinary light is reflected by the surface of a transparent medium like glass or water, the reflected light is partially polarized. The degree of polarization depends on the angle of incidence.
As the angle of incidence is gradually increased from a small value, the degree of polarization also increases. At a particular angle of incidence the reflected light is completely plane polarized.
This angle of incidence is called Brewster’s angle or polarizing angle (iB).
If the angle of incidence is further increased, the degree of polarization decreases.