Name: Ray Diagram: Lenses
Uploaded: 2019-07-19
Duration: 6 min 35 s
Description: In this video, let us discuss how ray diagrams for lenses can be used to determine the size and location of a refracted image. Get in to know more!

Question

Discuss the refraction through a rectangular glass slab and show that the emergent ray is parallel to the incident ray but laterally displaced. How does lateral displacement depend on the thickness of the glass slab?

Accepted Answer

Consider a rectangular glass slab PQRS, as shown in figure below. On the face $PQ$ , a ray $AB$ is an incident at an angle of incident $i_{1}$ . It bends towards the normal entering the glass slab, and travels along $BC$ inclined at an angle of refraction $r_{1}$ .

The refracted ray $BC$ is incident on the face $SR$ at an angle of incidence $i_{2}$ . The emergent ray $CD$ bends away from the normal at an angle of refraction $r_{2}$ .

Since $r_{1} = i_{2},$ therefore $i_{1} = r_{2}$ (because the law of refraction is same at the both interface.)

Therefore emergent ray $CD$ is parallel to the incident ray $AB$ , but it has been laterally displaced by a perpendicular distance $CN$ with respect to the incident ray.

This lateral shift in the path of light on emerging from a medium with parallel faces is called lateral displacement.

It is found that the lateral displacement is directly proportional to the thickness of the glass slab.

Discuss the refraction through a rectangular glass slab and show that the emergent ray is parallel to the incident ray but laterally displaced. How does lateral displacement depend on the thickness of the glass slab?

Important Questions on Light - Reflection and Refraction

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