Question

How does refraction of light cause a rainbow to form?

Answer 1

The same way a rainbow is created in a prism

Explanation:

Here is a picture of light refracting in a prism.
When light refracts it changes the direction it's going. This happens when light goes from one medium to another. For example from air into glass. When this happens light slows down and turns a bit.

The reason for it refracting into different colors is because different colors have different wavelengths and therefore refracts in different angles. As u see in the picture, red is "turning" slower than violet making red being on top and violet in the bottom.

You have probably noticed that a rainbow only shows when it's sunny and rains. The same thing happens in the air when these conditions are met. The light refracts in the raindrops, projecting what is seen as a rainbow in the sky.