Colour and Dispersion

White light is a mixture of many visible wavelengths. Different visible wavelengths are perceived as different colours.

**Dispersion** is the separation of white light into its component colours because different wavelengths are refracted by different amounts. A glass prism can produce a visible spectrum.

A common visible sequence is: red → orange → yellow → green → blue → violet

The refractive index of glass varies slightly with wavelength. Therefore, different colours travel at different speeds inside the material and are refracted by different amounts.

In ordinary glass: red light is generally deviated less; violet light is generally deviated more.

Rainbows involve refraction, dispersion, and internal reflection in water droplets.

An object appears a particular colour because it reflects or transmits certain wavelengths more strongly than others. A red object under white light reflects mainly red wavelengths and absorbs many others.