Question

why does light dispered by rain drops appear as a bow

Answer 1

Basically light is made up of seven colours. when light is passed through rain drop it splits up and we got seven colours or rain bow.

Answer 2

Every raindrop disperses VIBGYOR in white light. However, each raindrop disperses each colour at a specific angle with respect to incident light. That is why light dispersed by raindrops appear bow