Question

A ray of light travels from water to air as shown in the diagram given.
(i) Copy the diagram and complete the path of the ray. Given the critical angle for water is ${48}^o$.
(ii) State the condition so that total internal reflection occurs in the diagram.

Answer 1

The path of each is ray is shown in the above diagram when they pass through the air-water interface.

(i) : Since the critical angle for water air surface is ${48}^o$. So the rays, for which angle of incidence is less than ${48}^o$, will get refracted at the surface. While the ray for which angle of incidence is greater than ${48}^o$ will get total internally reflected.

Also, the given has angle of incidence exactly as ${48}^o$. So it grazes over the water air interface as shown.

(ii) : There are two condition for total internal reflection to occur.

(a) : The light ray must travel from denser medium to rarer medium but not vice- versa.

(b) : Angle of incidence of the ray must be greater than the critical angle. So total internal reflection of ray will occur is $\angle i>{48}^o$.