The rainbow formation in the sky is the combined effect of the refraction, dispersion, and total internal reflection of light.
(1) The sunlight is a mixture of seven colours,. The atmosphere contains a large number of water droplets after raining stopped.
When sunlight is strike on a water droplet, there is
- refraction and dispersion of light as it passes from air to water
- internal reflection of light inside the droplet and
- refraction of light as it passes from water to air.
(2) The refractive index of water is different for different colours, being maximum for violet and minimum for red. Hence, there is dispersion of light into different colours as it passes from air to water. As shown in Fig
(3) The combined action of different water droplets, acting like tiny prisms, is to produce a rainbow with red colour at the outer side and violet colour at the inner side. The remaining five colours lie between these two.
We see the rainbow when the sun is behind the us and water droplets in the front.
