Dispersion

Now that we understand refraction as due to the change in the speed of light as it enters a more dense medium, we can also understand what causes dispersion. All colours of light go at the same speed in vacuum, but they travel at different speeds inside matter. For example, blue light travels a bit faster, in general, than red light. This in turn makes the blue light bend more, and the colours go their separate ways, as indicated in Fig.10.1.3.