State the conditions of total internal reflection. Refractive indices of the given prism material for Red, Blue and Green colours are respectively 1.39, 1.48 and 1.42 respectively. Trace the path of rays through the prism.

Total internal reflection is the phenomenon of complete reflection of the light when reaches to the interface of the less dense medium provided that the angle of incidence is greater than the critical angle.

Where, is the refractive index of the denser medium and is the refractive index of the rarer medium.

Conditions of total internal reflection are as follows:

 The light should travel from denser medium to rarer medium

 The angle of incidence should be greater than the critical angle

Now, when the three lights rays of different colour fall on the AB face of prism then the lights rays will not reflect back from the face AB. The red ray will emerge out of the prism and blue and green undergoes total internal reflection.

It is because the refractive index of the red id minimum hence, the critical angle for red colour is maximum. Except red, blue and green will incident on the Ac face of prism at more than critical angle