Question

Explain the refraction of light through a rectangular glass slab.

Hint:

In a rectangular glass slab, the {incident ray and emergent ray are parallel}, but the emergent ray is laterally displaced from the original path.

Answer 1

Concept: Refraction of light is the change in direction of light when it passes from one medium to another due to a change in its speed. In a rectangular glass slab, refraction occurs at both surfaces of the slab.
Step 1:Refraction at the first surface} When a ray of light passes from air into the glass slab, it travels from a rarer medium (air) to a denser medium (glass). Therefore, the ray bends towards the normal. This bending of light at the boundary is called refraction.
Step 2:Refraction at the second surface} When the light ray travels inside the slab and reaches the second surface, it moves from a denser medium (glass) to a rarer medium (air). Hence, the ray bends away from the normal.
Step 3:Lateral displacement} After emerging from the slab, the emergent ray becomes parallel to the incident ray, but it is shifted sideways. This sideways shift of the ray is called lateral displacement. Thus, in a rectangular glass slab, light undergoes refraction at both surfaces and the emergent ray remains parallel to the incident ray with a lateral displacement.