|At what angles do light rays reflect out of a prism? — BC, Farmersville, TX
It depends on the shape of the prism and the angle at which the light arrived at the prism. Whenever light's speed changes as it passes through a surface at an angle, the light bends. Since light travels faster in air than in glass (or plastic), it bends when it goes from air to glass or from glass to air. When light enters glass, it slows down and it bends toward the normal to the surface (toward the line that's at right angles to the surface). When light leaves glass, it speeds up and it bends away from the normal to the surface. To know exactly how far the light bends, you need to know how much the glass slows light (the glass's refractive index) and the angle at which the light encountered the glass surface (the angle of incidence). You can then use one of the basic laws of optics, Snell's law, to determine the angle at which the light continues through the glass. You can then do the same for the light's emergence from the glass and determine the angle at which it leaves.