Question

An isosceles prism of angle 120° has a refractive index 1.44. Two parallel monochromatic rays enter the prism parallel to each other in air as shown. The rays emerge from the opposite faces:

Options

• are parallel to each other

• are diverging

• make an angle 2[sin⁻¹ (0.72) − 30°] with each other

• make an angle 2 sin⁻¹ (0.72) with each other

Answer 1

make an angle 2[sin⁻¹ (0.72) − 30°] with each other

Explanation:

Applying Snell's law at P,

µ = `(sin "r")/(sin 30°)`

sin r = `1.44/2` = 0.72

∴ δ = r − 30° = sin⁻¹ (0.72) − 30°

∴ The rays make an angle of 2δ = 2[sin⁻¹ (0.72) − 30°] with each other.