31.4 Dispersion by Benjamin Crowell, Light and Matter  licensed under the Creative Commons Attribution-ShareAlike license.

31.4 Dispersion

For most materials, we observe that the index of refraction depends slightly on wavelength, being highest at the blue end of the visible spectrum and lowest at the red. For example, white light disperses into a rainbow when it passes through a prism, q. Even when the waves involved aren't light waves, and even when refraction isn't of interest, the dependence of wave speed on wavelength is referred to as dispersion. Dispersion inside spherical raindrops is responsible for the creation of rainbows in the sky, and in an optical instrument such as the eye or a camera it is responsible for a type of aberration called chromatic aberration (section 30.3 and problem 2). As we'll see in section 35.2, dispersion causes a wave that is not a pure sine wave to have its shape distorted as it travels, and also causes the speed at which energy and information are transported by the wave to be different from what one might expect from a naive calculation.

31.4 Dispersion by Benjamin Crowell, Light and Matter  licensed under the Creative Commons Attribution-ShareAlike license.