Why does a ray of light bend towards normal when it enters from air into a glass slab and bends away from normal when it emerges out into air?

Explanation:

When a ray of light passes from one medium to another, it undergoes a change in speed and direction. The bending of light as it passes from one medium to another is known as refraction. Refraction occurs due to the change in the speed of light in different mediums.

Refraction at the Air-Glass Interface:

When a ray of light enters a glass slab from air, it undergoes refraction. The following factors explain why the ray bends towards the normal:

1. Change in Speed: The speed of light is different in air and glass due to the difference in their refractive indices. The refractive index is a measure of how much a medium can slow down the speed of light. Glass has a higher refractive index than air, so the speed of light decreases when it enters the glass slab.

2. Change in Direction: As the speed of light decreases upon entering the glass, the ray bends towards the normal. This is because the change in speed causes a change in the direction of the ray. According to Snell's law, the angle of incidence (the angle between the incident ray and the normal) is related to the angle of refraction (the angle between the refracted ray and the normal) by the equation: n1*sin(angle of incidence) = n2*sin(angle of refraction), where n1 and n2 are the refractive indices of the initial and final mediums, respectively.

3. Higher Optical Density: Glass has a higher optical density compared to air, which means it can slow down the speed of light more effectively. This higher density causes the bending of the ray towards the normal.

Refraction at the Glass-Air Interface:

When a ray of light emerges from the glass slab into air, it undergoes refraction again. This time, the ray bends away from the normal. The following factors explain this phenomenon:

1. Change in Speed: As the ray of light exits the glass slab and enters air, its speed increases since air has a lower refractive index than glass. The increase in speed causes the ray to bend away from the normal.

2. Change in Direction: The increase in speed upon entering air causes a change in the direction of the ray. The angle of refraction is greater than the angle of incidence, causing the ray to bend away from the normal.

3. Lower Optical Density: Air has a lower optical density compared to glass, which means it cannot slow down the speed of light as effectively. This lower density leads to the bending of the ray away from the normal.

Overall, the bending of light towards the normal when entering a glass slab from air, and away from the normal when emerging from the glass slab into air, is a result of the change in speed and direction of the light ray due to the difference in refractive indices and optical densities between the two mediums.

As it goes from one medium to another the speed of light changes and thus refract.