Distinguish between unpolarised light and linearly polarised light. How does one get linearly polarised light with the help of a polaroid ?

Explanation

An unpolarised light consists of many independent waves, whose planes of vibration are randomly oriented about the direction of propagation as shown in Fig.

Light is generally represented by electric field vector `vec(E)`, called light vector.
Linearly polarised light is that in which vibrations of electric field are confined in one direction in a plane perpendicular to the direction of propagation of light.
when unpolarised light is passed thorugh a tounmaline crystal cut with its face parallel to the crystallographic axis, only those vibrations of light pass through the crystal, which are parallel to the axis. All other vibrations are absorbed and we get linearly polarised light.