Question

If the angle of incidence is equal to the critical angle, then the angle of refraction is (C):
(A) \[{0^0}\]
(B) \[{20^0}\]
(C) \[{90^0}\]
(D) \[{180^0}\]

Answer 1

: Hint :The critical angle for reflected light is observed only when the light ray is travelling from a denser medium to a rarer medium. When the incident light hits at the critical angle, the refracted ray moves along the interface joining the 2 mediums.

Complete step-by-step solution:
When a light ray goes from a denser medium to rarer medium it bends away from normal and as the angle of incidence in the denser medium increases, the angle of refraction in the rarer medium also increases, and at a certain angle, the angle of refraction becomes \[{90^0}\] , this angle of incidence is called the critical angle.


According to the definition when the incidence angle is equal to the critical angle the refracted ray passes along the line separating the two medium making the angle of refraction \[{90^0}\]

Hence the angle of refraction is \[{90^0}\] and the correct option is C.

Note: When the light passes from denser medium to rarer medium with an angle of incidence greater than the critical angle for the pair of medium a phenomenon called total internal reflection takes place where the light ray returns to the denser medium.