Why does light get polarised when reflected and refracted?
A quick answer :
Light is a transverse wave, which means that the electric field (as well as the magnetic field) is perpendicular to the direction of propagation of light (at least in isotropic media - but let's keep things simple here).
So when light is incident obliquely on the boundary of two media, the electric field can be thought of as having two components - one in the plane of incidence, and one perpendicular to it. For unpolarized light, the direction of the electric field fluctuates randomly (while staying perpendicular to the direction of propagation) and as a result, the two components are of equal order in size.
How much of each component is transmitted and reflected can be figured out by using the laws of electromagnetism. Without going into the mathematical details here let me quote a result - the
The other, so called
So, when light is incident at the Brewster angle - the reflected beam has no component in the plane of polarization. It is entirely
For angles of incidence close to the Brewster angle, the reflected beam has a lot more
The transmitted beam has both components and hence is never completely polarized. However, at the Brewster angle, all of the