Refraction through a Glass Slab:
Refraction is the bending of light as it passes from one medium to another. When light passes through a glass slab, it undergoes refraction due to the change in its speed. The glass slab is a transparent medium with a higher refractive index compared to the surrounding medium (usually air).

Refraction Process:
When a ray of light enters a glass slab, it slows down and bends towards the normal (an imaginary line perpendicular to the surface of the slab). This bending of light is known as refraction. The extent of bending depends on the refractive indices of the two media involved.

Diagram:
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Key Points:
- The ray of light incident on the glass slab is called the incident ray.
- The ray that enters the glass slab is called the refracted ray.
- The normal is an imaginary line perpendicular to the surface of the slab at the point of incidence.
- The angle between the incident ray and the normal is the angle of incidence.
- The angle between the refracted ray and the normal is the angle of refraction.

Refraction Index:
The refractive index of a medium is a measure of how much the speed of light is reduced when it passes through that medium. It is denoted by the symbol 'n' and is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium.

Mathematically, the refractive index (n) is given by:
n = c/v
where 'c' is the speed of light in a vacuum and 'v' is the speed of light in the medium.

Key Points:
- The refractive index of a vacuum or air is approximately 1.
- The refractive index of a medium is always greater than or equal to 1.
- The refractive index determines the bending of light when it enters a medium.
- Different materials have different refractive indices, which affect the amount of bending.

Conclusion:
Refraction through a glass slab occurs when light passes from one medium to another with a higher refractive index. The bending of light is caused by the change in speed as it enters the glass slab. The refractive index of a medium is a measure of how much the speed of light is reduced in that medium compared to a vacuum or air. Understanding the concept of refraction and refractive index is crucial in various applications, including optics and lens design.