Sunlight is refracted when it passes through a prism because of the change in speed of light as it moves from one medium to another.

Sunlight is white light consisting of seven different colors which have different velocities in a denser medium due to their different magnitudes of wavelength. When light enters the prism from air (a less dense medium) into glass (a denser medium), it slows down and bends towards the normal line. This bending occurs at both the entry and exit points of the prism.

Since a prism has angled surfaces, the light rays do not exit parallel to their original direction; instead, they are deviated, resulting in a separation of colors due to different wavelengths of light being refracted by varying amounts. This phenomenon is known as dispersion of light, where white light splits into its constituent colors, creating a spectrum.