Physics-2 semester-Polarisation of light

Light is a electromagnetic radiation.

Ordinary light:It is unpolarised light.

Polarised light: Vibration will be in only one plane.

When light passes through polarizer ( quartz glass) then polarisation of light takes place.

Polarisation of light: When unpolarised light transforms into polarised light then the process is known as polarisation of light.

Optical axis:Axis which  decides the plane in which light get polarised.

Plane of vibration:Plane contains the direction of propogation of light and direction of vibration of light.

From Fig.ABCD is the plane of vibration.

ABCD perpendicular to EFGH.

Plane of polarisation: This plane contains only direction of propogation of light.

From Fig.EFGH is the plane of polarisation.

Doubly refracting crystal:There are certain crystal by which two types of plane polarised light rays are obtained when unpolarised light incident upon it. Such type of crystals are known as doubly refractive crystal.

Ther are two types of doubly refractive crystals:

1) Uniaxial: It has single optical axis.

Ex: Calcite; quartz.

2) Biaxial: It has two optical axis.

Ex: Topaz; Aroganite.

Double refraction phenomenon

When unpolarised light is incident on the doubly refracting crystal then two types of plane polarised light rays are obtained.

Such type of phenomenon of refraction is known as double refraction phenomenon.

In two types of refracting rays,

One ray obey  law of refraction and is same in all directions is known as ordinary ray.(O ray)

One ray does not obey  law of refraction and it's velocity is different in different direction is known as extraordinary ray.(E ray)

Birefractive Property: It depends upon refractive index, the polarisation of light and direction of polarised light.