why there is a rainbow?

Answer 1

Sunlight is not pure white light, its actually made up of colours (from indigo to red). To see the colours, the light has to pass through a prism (a shaped clear object like a crystal or a raindrop).

After a rainstorm there is still a lot of tiny water droplets still high up in the air, and when sunlight shines through them and we are the right angle, the sunlight is split up into what we call a rainbow - the colours of the sunlight spread out so we can see each one separately instead of all together (which just looks white).
The arched shape of the rainbow is because each of those colours is bent by the raindrops by a slightly different amount.

Answer 2

On a rainy day,sunrays which contain all the seven colours,fall on water droplets at a certain incident angle and refract with certain other refractive angle, because water is denser than air.The angle of refraction,however, is different for different colours of the rays.So the the sun's ray gets dispersed into seven colours of the visible light as the light beam is refracted into the body of the water droplet.
The colours, thus dispersed undrergo total internal reflection on the opposite inner side of the droplet and reach the eye to enable us see the virtual image of the rainbow .
In normal clouds, the droplets are too small to cause sufficient resolution of the colours and the total internal reflection.Hence rainbow is invisble with dry clouds.But, on a rainy day, the droplets are big enough to cause the resolution and total intenal reflection of the colours to enable us to see the rainbow.

Answer 3

Refraction of light through a water molecule