PRISMS

So far in our discussion of refraction, we have considered only beams of light of one color, one wavelength. Because the index of refraction generally changes with wavelength, rays of different wavelength will be bent at different angles when passing the interface of two media. Usually the index of refraction of visible light increases as the wavelength becomes shorter. Thus when white light, which is a mixture of all the visible colors, is sent through a prism as shown in Figure (1), the short wavelength blue light will be deflected by a greater angle than the red light, and the beam of light is separated into a rainbow of colors.

Figure 1: When light is sent through a prism, it is separated into a rainbow of colors. In this scale drawing, we find that almost all the separation of colors occurs at the second surface where the light emerges from the glass.