Types of Interference:

Constructive Interference

When two waves travelling together are in phase then these reinforce each other. The amplitude of the resultant wave is more than that of any of the two waves.

Actully it is the sum of the amplitudes of the two waves.

Destructive Interference

When two waves travelling together are out of phase then these cancel each other. The amplitude of the resultant wave is equal to the sum of the amplitudes of the two waves. In this case the waves are fully out of phase the waves are destroyed completely.

Reflection of Light

When a radiation travelling in a given medium is incident on a medium of different refractive index at an angle; then a fraction of the radiation bounces back at an angle equal to the angle of incidence of the radiation. This is known as reflection of light.

Refraction of Light

The change in the direction of a beam of light when it falls on the interface of two transparent media of different densities is called refraction.