When light travels from one medium to another, such as from air to glass or water, its speed changes. This change in speed causes the light to bend, or refract.
The amount of bending depends on the difference in the refractive indices of the two mediums. The refractive index is a measure of how much a medium slows down light.
The greater the difference in refractive indices, the greater the amount of bending. For example, light bends more when it travels from air to glass than when it travels from air to water because glass has a higher refractive index than water.
The bending of light is also affected by the wavelength of the light. Shorter wavelengths, such as blue light, bend more than longer wavelengths, such as red light. This is why we see a rainbow when sunlight passes through water droplets in the air. The different wavelengths of light are refracted at different angles, causing the light to be separated into a spectrum of colors.
