Question

Darken a room and pass a narrow beam of light through a prism. Allow the emerging light to fall on a screen or a wall (Fig.). Note the colours you see.

Now, place another prism upside down in the path of the dispersed light. What do you observe now? Do you see a patch of light?

Answer 1

Yes, a patch of white light is observed. When the dispersed colours from the first prism pass through a second prism placed upside down, the colours are deviated in the opposite direction and recombine to form white light. This process is called recombination of light. It shows that white light is made up of different colours and that a prism only separates these colours; it does not produce them.