first light enters the glass slab from a rarer medium(air). at the point of refraction the light gets deviated due to the presence of denser optical medium which reduces the speed of light..thus refraction takes place and when the light again strike the other face of the slab the vice versa happens i.e the light now travel from a denser medium to a rarer medium thus angle of emergent ray =angle of incidence..

Refraction through Rectangular Glass Slab:

Refraction is the bending of light as it passes from one medium to another. When light enters a rectangular glass slab, it undergoes refraction due to the change in its speed and direction. Let's understand the process of refraction through a rectangular glass slab in detail:

1. Introduction:
- Refraction is the phenomenon that occurs when light travels from one medium to another, causing a change in its speed and direction.
- A rectangular glass slab is a transparent medium with parallel rectangular faces.

2. Incident Ray:
- The incident ray is the incoming ray of light that strikes the surface of the glass slab.
- It approaches the slab from one medium, called the incident medium, which could be air, vacuum, or any other material.

3. Refracted Ray:
- The refracted ray is the ray of light that emerges from the other face of the glass slab.
- It moves into another medium, known as the refracting medium, which could be air, water, or another material.

4. Normal:
- The normal is an imaginary line perpendicular to the surface of the glass slab.
- It is drawn at the point where the incident ray strikes the surface.

5. Angle of Incidence:
- The angle of incidence is the angle between the incident ray and the normal.
- It is denoted by the symbol 'i'.

6. Angle of Refraction:
- The angle of refraction is the angle between the refracted ray and the normal.
- It is denoted by the symbol 'r'.

7. Laws of Refraction:
- The incident ray, refracted ray, and the normal all lie in the same plane.
- The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media. This ratio is known as the refractive index.

8. Refractive Index:
- The refractive index of a material is the ratio of the speed of light in vacuum or air to the speed of light in that material.
- It is denoted by the symbol 'n' and is specific to each material.

9. Refraction through a Rectangular Glass Slab:
- When a ray of light enters a rectangular glass slab, it undergoes refraction twice, once at each surface of the slab.
- The incident ray bends towards the normal as it enters the slab, and then it bends away from the normal as it exits the slab.

10. Deviation:
- The deviation is the angle between the incident ray and the emergent ray.
- It depends on the thickness of the glass slab and the refractive index of the material.

11. Total Internal Reflection:
- Total internal reflection occurs when the angle of incidence is greater than the critical angle.
- In such cases, the light does not leave the glass slab but is reflected back inside.

12. Practical Applications:
- Rectangular glass slabs are used in optics and physics experiments to study the phenomena of refraction and total internal reflection.
- They are also used in the construction of optical instruments like microscopes, telescopes, and lenses.

In conclusion, refraction through a rectangular glass slab involves the bending