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

A light ray incident on a rectangular glass slab emerges parallel to itself due to the laws of refraction. Here's a step-by-step explanation:

1. When a ray of light hits the surface of the glass slab, it slows down and bends towards the normal line due to the change in medium from air (or any other medium) to glass. This is according to Snell's law of refraction, which states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.

2. As the ray of light exits the glass slab, it speeds up and bends away from the normal line, again due to the change in medium from glass to air (or the original medium). The angle of incidence (when the light ray exits the slab) is equal to the angle of refraction (when the light ray entered the slab).

3. Because the angles of incidence and refraction are equal, and the sides of the glass slab are parallel, the light ray emerges from the slab parallel to the path it was on when it entered the slab.

Here's a simple diagram to illustrate this:

|  /     /|
| /     / |
|/     /  |
|     /   |
|  /     /|
| /     / |
|/     /  |

In this diagram, the vertical lines represent the parallel sides of the glass slab. The diagonal lines represent the path of the light ray. As you can see, the light ray enters and exits the slab at the same angle, making the incoming and outgoing paths parallel.