Describe how you could demonstrate that white light is composed of a number of colours.

We can demonstrate that white light is composed of a number of colours, by allowing a beam of white light to pass through a triangular glass prism. When a beam of white light enters the prism, it splits, to form a band of seven colours on a screen placed on the other side of the prism. This phenomenon of splitting white light into its components colours (violet, indigo, blue, green, yellow, orange, and red) is known as the dispersion of light.

The formation of seven colours in a spectrum shows that white light is composed of these seven colours.