In given figure, a light ray AB is incident normally on one face PQ of an equilateral glass prism.

Find out the angles at faces PQ and PR.

Angle of incidence, i = 0^o

Angle of refraction, r = sin(i)×n

Where n = refractive index

So, r₁ = 0^o

Where,

r₁ = angle of refraction at PQ

r₂ = angle of incidence from inside on side PR

A = angle of prism

We know that

A = r₁ + r₂

r₂ = A – r₁

= 60^o – 0^o

= 60^o