2014-09-13T20:50:50+05:30 it forms as:_
u know when it rains then the water falls down but some moisture is left behind for eg.....u must have seen a strong waterfall if not see a pic when the water reaches the surface with pressure then the smoke iss produced actually it is not fogg or smoke it is only small small particles of water okayy now........when water get condesed it formes cloud then rain so rain also comes with some pressure it leaves some particles of water then the sun acts as a torch ..i mean to say it throws rays of light each ray passes through a drop of water and that drop of water acts as a prizm u know that prizm reflects white or sunlight into 7 different colours thats how the raindrops do they also reflect the light and ech drop reflects to another that makes a big network of colours called the RAINBOW !!!!
The water droplets act as a prism which splits the white light into seven constituent colours and this causes the formation of rainbow as an after effect of rain when the sun shines.