Question

A ray of light passes through an equilateral glass prism such that the angle of incidence is equal to the angle of emergence and each of these angles is equal to 3/4 of angle of prism. Find the angle of deviation.

Answer 1

The angle of deviation δ for a ray of light in a prism is given by

δ=i+e−A

where
i = Angle of incidence of ray
e = Its angle of emergence 
A = Angle of prism

`∵e=i`

` ⇒δ=2i−A`

Given:` i=e=3/4A`

`∴δ=2×3/4A−A`

`⇒δ=1/2A`

As the prism is equailateral,⇒A=60°

`∴δ=12×60°`

`⇒δ=30`