Question

A ray of light which is incident in air on the surface of a glass block is deviated through 15°. The angle of incidence in air is 60°. What is the angle of refraction in glass? Also calculate the critical angle for the glass-air interface.

Answer 1

Given: Angle of incidence, i = 60°

Deviation, δ = 15°

Therefore, angle of refraction,

r = i − δ

= 60° − 15°

= 45°

1. Refractive index using Snell’s law:

n = `sin i/sin r`

= `(sin 60°)/(sin 45°)`

= `0.866/0.707`

≈ 1.224

2. Critical angle C:

sin C = `1/n`

sin C = `1/1.224`

sin C ≈ 0.816

C = sin⁻¹ (0.816)

C ≈ 54.7°

Hence, the angle of refraction is 45° and the critical angle for the glass-air interface is 54.7°.