Question

A ray of light LM incident normally on the surface AC of an isosceles right angled prism ABC (where AB = BC) emerges along PQ, parallel to LM, as shown in the figure below. What can you say about the refractive index µ of the material of the prism?

Answer 1

∠A = ∠C = 45°  ....(isosceles right angled triangle)

∴ ∠i = 45°

For total internal reflection to take place at faces `sin i > 1/n`, where n is the refractive index of the prism with respect to air.

sin 45° > `1/n`

`n > 1/(sin 45°)`

`n > sqrt2`

Hence, the refractive index of the prismm is greater than `sqrt2`.