Question

A right angle prism PQR is made of a material of refractive index 1.67. AB is ray incident normally on face PQ as shown in Fig. Which of the following statements is correct?

(1) AB emerges out of face PR of prism

(2) AB undergoes a deviation of 60° on face PR of prism

(3) Ray AB, emerges out of face QR at an angle of emergence of 45°

(4) Ray AB emerges out of face QR normally

Answer 1

(2) AB undergoes a deviation of 60° on face PR of prism

The critical angle of incidence, i_e , inside the prism is given by

The angle of incidence on face PR is 60° . This is more than i_c ; hence T.I.R occurs at face PR.

The angle of deviation = 180° - 120° = 60°

The totally reflected ray CD, is incident at 30° , at point D, on face QR. The angle emergence, e, is given by is

Hence statements (3) and (4) are seen to be incorrect. It is only statement (2) that is correct.