Question

When a ray of light is incident normally on one refracting surface of an equilateral prism of refractive index 1.5, the emerging ray ______.

`[sin^-1(1/1.5)=41.8^circ]`

Options

• undergoes total internal reflection at second refracting surface

• just grazes the second refracting surface

• is deviated by 30°

• is deviated by 20°

Answer 1

When a ray of light is incident normally on one refracting surface of an equilateral prism of refractive index 1.5, the emerging ray undergoes total internal reflection at second refracting surface.

Explanation:

If C is the critical angle then

`sinC=1/1.5`

`thereforeC=sin^-1(1/1.5)=41.8^circ`

For a prism A= r₁ + r₂

For normal incidence i = 0

∴ r₁ = 0

∴ r₂ = A = 60°

r₂ is the angle of incidence on the second surface of the prism.

Since r₂ > C, the ray will undergo total internal reflection at the second surface.