Why does a light ray incident on a rectangular glass slabimmersed in any medium emerge parallel to itself? Explainusing a diagram

When a ray of light hits a rectangular glass slab, it undergoes a series of refractions due to the change in medium. Here's a step-by-step explanation:

1. As the light ray hits the surface of the glass slab, it moves from a rarer medium (air) to a denser medium (glass). This causes the light ray to bend towards the normal line (an imaginary line perpendicular to the point of incidence).

2. The light ray then travels through the glass slab and hits the opposite surface. At this point, it moves from a denser medium (glass) to a rarer medium (air). This causes the light ray to bend away from the normal line.

3. Due to the parallel nature of the two surfaces of the glass slab, the angle of incidence at the first surface is equal to the angle of emergence at the second surface. This is due to the laws of refraction, which state that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant (Snell's Law).

4. As a result, the emergent ray is parallel to the incident ray. This is because the angles of incidence and emergence are equal, and the two rays are on the same plane.

Here's a simple diagram to illustrate this:

Normal
  ^
  |
  |
  |     / Emergent ray
  |    /
  |   /
  |  /  
  | /  
  |/ Incident ray
  |------------------> Glass slab

In this diagram, the incident ray hits the glass slab and is refracted, changing its direction. As it exits the slab, it is refracted again and emerges parallel to the original direction.