PHYS102: Introduction to Electromagnetism

A rainbow is the most familiar natural phenomenon that demonstrates dispersion. The light from the sun contains waves with all frequencies of the visible spectrum. The combination of all these waves is perceived as white light. If there are water droplets in the air, the light refracts when it enters the droplets, and then refracts again as it leaves the droplets. Since the angle of refraction is different for light of different frequencies, waves of different colors separate. We perceive this as a rainbow.

Watch this short video on differently-colored light rays as they get refracted by different amounts.