The Human Eye and the Colourful World

In order to get white light from the dispersed light the prisms are arranged as shown in the diagram.

Recombination of the seven colours of the dispersed white light to get white light is known as recomposition of white light.

Experiment to Show the Recomposition of White Light

Place a prism (P₁) on a table and a screen behind it. Allow a narrow beam of light to be incident on the prism (P₁). The white light gets dispersed and we obtain a band of seven colours on the screen.

Now remove the screen and place another prism P₂ of the same material in the opposite direction. Place a white screen behind P₂. A spot of white light appears on the screen. Thus the second prism has recombined the dispersed light.

Formation of a Rainbow

The small droplets of rain water which remain suspended in air just after the rains act like a prism. When sunlight passes through these drops of rainwater, it gets dispersed and we see the seven colours of the rainbow.