Answer the follow

When a ray of light, travelling from an optically denser medium into an optically rarer medium is incident at an angle greater than the critical angle for the two media, the ray is totally reflected back into the medium, obeying the laws of reflection. This phenomenon is called total internal reflection.

Two important conditions for total internal reflection are:

1. The angle of incidence (i) should be greater than the critical angle (i_c).

2. Ray should travel from denser medium to rarer medium.

The critical angle is that angle of incidence in a denser medium, for which the angle of refraction in the rarer medium is 90 °.The figure below illustrates the critical angle and total internal reflection.