Question

What is refraction of light and under what circumstances does it occur?

Answer 1

Light has different velocities in different media

(eg :the velocity of light in water is different than the velocity of light in air)

This is because every medium has a special property called optical density, which affects the velocity of light in that medium.

Optical density is inversely proportional to the velocity of light

(optical density of diamond >glass>water>air )
(velocity of light in air>water>glass>diamond )

Which means, light's velocity depends on the medium by which it transmits.

So whenever light travels through two different media of different optical density, the velocity of light changes. This leads to a bending phenomenon. This is refraction, in other words refraction is an optical phenomenon of bending of light at the interface of the media when light enters obliquely from one medium to another medium of different optical density.

so if refraction has to occur

Light should enter obliquely from one medium to another medium of different optical density

The medium with lower optical density is called rarer medium and with higher optical density is called denser medium.

1. Refraction from denser to rarer

The refracted ray deviates away from the normal

2.refraction from rarer to denser

The refracted ray deviates towards the normal