The phenomenon of interference and diffraction establishes the wave nature of light. Both these phenomena are exhibited by both the types of wave motion i.e., longitudinal and transverse.
In transverse wave motion the vibrations of particles take place in a direction perpendicular to the direction of propagation of the wave. Hence the vibration in ordinary light are distributed symmetrically in all directions in a plane perpendicular to the direction of propagation. Such light is called unpolarised light.
Light waves which exhibit different properties in different directions are called polarised light waves. This can be demonstrated by using a pair of tourmaline crystals in the path of light waves.
