(a) How does one demonstrate, using a suitable diagram, that unpolarised light when passed through a Polaroid gets polarised?
(b) A beam of unpolarised light is incident a glass-air interface. Show using a suitable ray diagram, that light reflected from the interface is totally polarised, when `mu=tani_(B)`, when `mu` is the refractive index of glass with respect to air and `i_(B)`, is the Brewster's angle.

Explanation

A polaroid consists of long chain molecules aligned in a particular direction. The electric vectors along the direction of the aligned molecules get absorbed. So, when an unpolarised light falls on a polaroid, it lets only those of its electric vectors that are oscillating along a direction perpendicular to its aligned molecules to pass through it. The incident light thus gets linearly polarised.

Whenever unpolarised light is incident on the boundary between two transparent media, the reflected light gets partially or completely polarised. When reflected light is perpendicular to the refracted light, the reflected light is a completely polarised light.