Question: How and why do prisms split the colour spectrum?

Julie Greensmith answered on 22 Jun 2011:

This is not my field at all but I used to enjoy this subject of optics at school so here goes:

This is because of a process called refraction, it is what happens when a beam of light goes from one medium to another. If the surface the light is going into is shiney, like a mirror, the light is reflected.

Some of the light travels through into the new medium and in the case of the prism is bounced around inside the prism. Light, for example from a torch bulb, is a mixture of light at different *wavelengthsMATOMO_URL When light gets refracted, light at different wavelengths gets diffracted different amounts, separating out the different wavelengths of light in a visible spectrum. This is a process called *dispersionMATOMO_URL There are more wavelengths of light produced, but we only see the ones in the visible spectrum which we see as being red through to purple.