When lyt moves from rarer to denser medium it bends towards the normal and when lyt moves from denser to rarer medium it moves away from the normal.

When light travels from a rare medium to a denser medium, such as from air to glass or from air to water, it undergoes certain changes in its behavior. The change in medium causes the light to bend or change direction. This phenomenon is known as refraction.

Refraction of Light - From Rare to Denser Medium:
1. Definition of Refraction: Refraction is the bending of light as it passes from one medium to another, due to the change in its speed.
2. Change in Direction: When light enters a denser medium from a rarer medium, it slows down, causing the light rays to bend towards the normal (a line perpendicular to the interface between the two media) as they enter the denser medium.
3. Decreased Speed: The speed of light decreases in a denser medium compared to a rarer medium. The decrease in speed is due to the interaction of light with the particles of the medium.
4. Change in Wavelength: As the speed of light decreases, its wavelength also changes. The wavelength becomes shorter in a denser medium.
5. Change in Frequency: According to the wave equation, the product of wavelength and frequency is constant for a given wave. As the wavelength decreases, the frequency of light increases in a denser medium.
6. Angle of Incidence and Angle of Refraction: The angle of incidence is the angle between the incident ray and the normal, while the angle of refraction is the angle between the refracted ray and the normal. The angle of refraction is smaller than the angle of incidence when light travels from a rarer to a denser medium.

Refraction of Light - From Denser to Rarer Medium:
1. Change in Direction: When light travels from a denser medium to a rarer medium, it speeds up and bends away from the normal.
2. Increased Speed: Light travels faster in a rarer medium compared to a denser medium. The increase in speed is due to the decrease in the interaction of light with the particles of the medium.
3. Change in Wavelength: As the speed of light increases, its wavelength also changes. The wavelength becomes longer in a rarer medium.
4. Change in Frequency: As the wavelength increases, the frequency of light decreases in a rarer medium.
5. Angle of Incidence and Angle of Refraction: The angle of incidence is still the angle between the incident ray and the normal, while the angle of refraction is the angle between the refracted ray and the normal. The angle of refraction is greater than the angle of incidence when light travels from a denser to a rarer medium.

In both cases, the phenomenon of refraction occurs due to the change in the speed of light when it travels from one medium to another. This change in speed causes the light rays to bend and change direction. The extent of bending depends on the refractive indices of the two media, which is a measure of how much the speed of light changes in each medium.