Question

A wide slab consisting of two media of refractive indices n₁ and n₂ is placed in air as shown in the figure. A ray of light is incident from medium n₁ to n₂ at an angle θ, where sin θ is slightly larger than `1/n_1`. Take the refractive index of air as 1. Which of the following statement(s) is(are) correct?

Options

• The light ray enters air if n₂ = n₁.

• The light ray is finally reflected back into the medium of refractive index n₁ if n₂ < n₁.

• The light ray is finally reflected back into the medium of refractive index n₁ if n₂ > n₁.

• The light ray is reflected back into the medium of refractive index n₁ if n₂ = 1.

Answer 1

The light ray is finally reflected back into the medium of refractive index n₁ if n₂ < n₁.

The light ray is finally reflected back into the medium of refractive index n₁ if n₂ > n₁.

The light ray is reflected back into the medium of refractive index n₁ if n₂ = 1.

Explanation:

n₁ sin θ₁ = n₂ sin θ₂ = 1 sin θ₃

⇒ n₁ sin θ₁ = sin θ₃

As, `sin θ_1 > 1/n_1`

So, sin θ₃ > 1

⇒ Refraction in air is not possible.

As θ₁ > the critical angle for the n₁ - air interface, the light ray will never enter in air, whatever may be the value of n₂.