Question

The refractive indices of four media, as shown in the figure, are n₁, n₂, n₃ and n₄. AB is an incident ray. DE, the emergent ray, is parallel to the incident ray AB, then ________ .(A) n₁ = n₂
(B) n₂ = n₃(C) n₃ = n₄
(D) n₄ = n₁

Answer 1

we know, when a ray of light passes through a slab of refractive index n then emergent ray is parallel to the incident ray.
e.g., emergent angle, r = incident angle, i.

now, from Snell's law,
$\bf{\mu sin\theta=constant}$

e.g., $\bf{\mu_1sini=\mu_4sinr}$

here , $\mu_1=n_1$, $\mu_4=n_4$ and i = r

$n_1 = n_4$

therefore option (D) is correct.