Explain the phenomenon of refraction through a rectangular glass slab? explain with an activity?

Refraction is the change in the direction of light when it passes obliquely from one transparent medium to another due to a change in its speed.

When a ray of light enters a rectangular glass slab from air:

• The light ray travels from air (rarer medium) to glass (denser medium), so it bends towards the normal. This ray is called the refracted ray.
• The ray then travels through the glass slab.
• When it emerges from the glass into air, it bends away from the normal.
• Since the two opposite faces of a rectangular glass slab are parallel, the emergent ray is parallel to the incident ray.
• However, the emergent ray is slightly shifted sideways from its original path. This shift is called lateral displacement.

Activity to Demonstrate Refraction Through a Glass Slab

Aim: To observe the path of light through a rectangular glass slab and study lateral displacement.

Materials required:

A rectangular glass slab, a white sheet of paper, drawing pins, a pencil, ruler and a few optical pins.

Procedure:

1. Fix a white sheet of paper on a drawing board.
2. Place the rectangular glass slab on the paper and trace its outline as ABCD.
3. Remove the glass slab and draw an incident ray PQ meeting one face of the slab at point O.
4. Fix two pins vertically along the line PQ.
5. Place the glass slab back on its outline.
6. Looking through the opposite face of the slab, place two more pins such that all the pins appear to be in one straight line.
7. Remove the slab and pins. Mark their positions and join the points to trace the path of the incident, refracted and emergent rays.

Observation: The light ray bends towards the normal on entering the glass and away from the normal on emerging into air. The emergent ray is parallel to the incident ray but is laterally displaced.

Conclusion: A rectangular glass slab causes refraction at both of its parallel surfaces, resulting in a parallel but laterally shifted emergent ray.