Question

how are rainbows formed

Answer 1

After the rain a number of small droplets of water remain suspended in the air. Each drop acts as a small prism. When sunlight falls on these drops the white light spills into seven colours. The dispersed light from a large number of drops forms a continuous band of seven colours. 
This coloured band is called a RAINBOW.

Answer 2

Answer:

A rainbow is formed when light (generally sunlight) passes through water droplets hanging in the atmosphere. The light waves change direction as they pass through the water droplets, resulting in two processes: reflection and refraction. When light reflects off a water droplet, it simply bounces back in the opposite direction from where it originated. When light refracts, it takes a different direction. Some individuals refer to refracted light as “bent light waves.” A rainbow is formed because white light enters the water droplet, where it bends in several different directions. When these bent light waves reach the other side of the water droplet, they reflect back out of the droplet instead of completely traversing the water. Since the white light is separated inside of the water, the refracted light appears as separate colors to the human eye.

Explanation: