Question

A light ray is incident perpendicular to one face of a 90° prism and is totally internally reflected at the glass-air interface. If the angle of reflection is 45°, we conclude that the refractive index n

(a) n<1/√2

(b) n>√2

(c) n>1/√2

(d) n<√2.

Answer 1

(b) : Total internal reflection occurs in a denser medium when light is incident at surface of separation at angle exceeding critical angle of the medium.
Given : i = 45° in the medium and total internal reflection occurs at the glass-air interface

Therefore, n>1/sinC >1/sin45^o >√2.