A ray of light is incident normally on one face of an equilateral prism of refractive index 1.5. What is the angle of deviation of the ray?

Let angle of deviation = δ

Where,

i = angle of incidence

e = angle of reflection

A = angle of prism

We also define,

r₁ = angle of refraction on incident face of prism

r₁ = angle of refraction on incident face of prism

Given,

i = 0

so, r₁ = 0

r₂ = 60⁰

critical angle = θ

Where μ = refractive index = 1.5

Since,

So there will be a total internal reflection,

The reflected ray is incident at the base at 90^o

So the angle of emergence = e = 0

Now angle of deviation is calculated as

So

Or