What is meant by
(a) 'Total internal reflection?
(b) State two essential conditions for total internal reflection to take place.
(c) With the help of a ray diagram, illustrate an application of total internal reflection.

Explanation

When light passes from one medium to other, it bends from its path which is called refraction. When a light ray passes from denser to rarer medium, at some angle of incidence it does not go out of the denser medium but just grazes along the boundary (i.e. angle of refraction = `90^(@)`). This angle of incidence is called critical angle.

Now, if you increase this angle of incidence, light ray is reflected back into the denser medium, which is called total internal reflection. The light ray is reflected everytime it hits the boundary because angle of incidence is equal to angle of reflection, and is not able to come out of the medium. This phenomenon is called total internal reflection. The conditions for total internal reflection are:
(i) the light ray must be travelling from optically denser medium to rarer medium and
(ii) the angle of incidence must be greater than the critical angle.
Optical fibres communication uses the principle of total -internal reflection for transferring data through optical fibres..