Question

Why does a light ray incident on a rectangular glass slab immersed in any medium emerges parallel to itself? Explain using a diagram.

Answer 1

Consider the diagram shown below in which EO is incident ray, OO' is refracted ray and O'H is emergent ray.

Here, AB is the air-glass interface and CD is the glass-air interface. The extent of bending of ray of light at opposite and parallel faces AB and CD of the rectangular glass slab is equal and opposite.
Here, angle i₁ = r₂ and angle r₁ = i₂
Hence, the ray emerges parallel to the incident ray.