Describe an activity to show that the colours of white light split by a glass prism can be recombined to get white light by another identical glass prism.

When a beam of white light incident on a prism, it disperses colours at different angles, known as dispersion. This beam will have a colour band, in which all the colours are arranged according to their wavelengths. If we arrange another prism in the opposite manner, then the dispersed colours merge into a white light beam again. When white light passes through a prism, a band of seven colours is obtained, which is called the spectrum. The seven colours in the spectrum are violet, indigo, blue, green, yellow, orange and red from down to up.