Rainbow is a beautiful and colorful phenomenon that occurs in nature. It is formed when sunlight passes through raindrops in the atmosphere. The formation of a rainbow can be explained by the following steps:
1. When white light travels from air to water droplet ( rarer to denser medium ) it changes its direction of propagation slightly. This causes the light ray to changes its velocity (slower down) and bend towards the normal. this Phenomenon is called the Refraction.
2. When white light experiences refraction, it splits into seven different colors ( Red , orange , Yellow ,Green , blue , indigo , violet - ROYGBIV). Since the wavelength for each color is different, Red will bend less ( Having Highest wavelength) and the violet will bend more ( having lowest wavelength ) .This phenomenon is called the dispersion of white light.
3. These dispersed rays again suffer a total internal reflection or bouncing back off from the opposite end of the water droplet.
4. After experiencing the final refraction from Water to air ( Denser to Rarer ) its velocity speedup and travels to our eyes. it makes a rainbow.
A rainbow is always formed in the direction opposite to that of the Sun. A rainbow requires water droplets to be floating in the air. That’s why we see them right after it rains. The Sun must be behind you and the clouds cleared away from the Sun for the rainbow to appear.
A full rainbow is actually a complete circle, but from the ground we see only part of it. From an airplane, in the right conditions, one can see an entire circular rainbow.