When a beam of white light is passed through a prism, it splits to form lights of seven colours. Is it possible to recombine the lights of seven colours to obtain the white light again? Explain your answer.

When a beam of white light is passed through a prism, it splits to form lights of seven colours. Yes, it is possible to recombine the lights of seven colours to obtain the white light again.

Recombination of colours to form white light again is possible if a second identical glass prism is placed in an inverted position behind the first prism. It recombines the spectrum obtained by the first prism and a beam of white light is obtained on a screen placed behind the second prism. It happens because the refraction produced by the second prism is equal and opposite to the refraction produced by the first prism.

Explanation

 When a glass prism is placed in the path of a narrow beam of white light, it gets dispersed into its seven constituent colours and a spectrum is obtained. Now, when a second identical prism is placed in an inverted position with respect to the first prism, it recombines the spectrum obtained by the first prism and a beam of white light is obtained again.