What word describes the bending of light as it enters and leaves a prisam?

Answer 1

When light traverse the interface between two transparent material with a different refraction index it undergo refraction, that is the angle of incidence on the interface is different from the angle with which the light comes out from the surface itself. In a prism refraction happens as the light passes from air to the prism material (generally glass or a polymer like PMMA, also called Plexiglas) and when the light leaves the prism, passing from it to air again.

Since the difference of incident and emerging angles is opposite passing from air to prism and from prism to air (let us call that angle q) the total diffraction angle due to the passage through a prism is 2 q.

Since q depends on the light wavelength (that is on the light color) different colors are diffracted at different angles and the light at the prism output appears as decomposed in different rays, exiting from the prism with different angles, one for each color.

Doping the prism glass with impurities increasing a lot its refraction index, complete refraction can be obtained for selected light colors. These colors at the first interface with the prism have a refraction angle greater than 90° and light of those colors does not enter into the prism. Thus colors suffering total refractions lack from the prism output light.