Look at the rainbow, it's a phenomena of the dispersion of light, because white light is consisted of light rays with other colors.
The great physicist, Issac Newton made this amazing discoveries with his famous "prism experiment".
Why the light rays of different colors disperse? What can analyze this from the snell's law.
sin θ2/sin θ1 = v2/v1 = n1/n2Different colors of light rays have different wavelengths, which gives them different refractive indexes. Eventually, light rays of different colors will be bent differently when they entering a medium. But the differences of their refractive indexes are actually very small.
The table below shows the refractive indexes of different colors of light of water.
| Color | Wavelength (nm) | Refractive index |
| Red | 700 | 1.33141 |
| Orange | 600 | 1.33393 |
| Yellow | 575 | 1.33472 |
| Green | 525 | 1.33659 |
| Blue | 475 | 1.34055 |
| Indigo | 425 | 1.34235 |
| Violet | 400 | 1.34451 |
The shorter the wavelength, the larger the refractive index
If the white light is a combination of different colors of light rays, why in most conditions, we only see the white? We can analyze it using our knowledge of the human eye.
When light rays of different colors are parallel to each other, they will be assembled by lens to a single white dot on our retina, and we can only see distinguish the light rays of different colors when they are not parallel to each other.