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Question

# What is "dispersion of white light"? Draw a labelled diagram to illustrate the recombination of the spectrum of white light.

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Solution

## Dispersion is the splitting up of white light into seven colours on passing through a transparent medium like a glass prism. When a white light beam is passed through a prism, a band of seven colours are formed which is known as a spectrum of white light. The seven colours in the spectrum are red, orange, yellow, green, blue, indigo and violet respectively. The dispersion of light occurs because the angle of refraction (or the angle of bending) of lights of different colours is different when passing through the transparent medium (glass prism). We know from the concept of dispersion of light, when a beam of white light incident on a prism, it disperses all the colours at different angles, So the emerging beam will be having a coloured band, in which all colours are arranged according to their wavelengths. If one more prism is arranged in opposite manner, then the dispersed colours will merge into white light beam again. This is shown in the figure below. All the colours will be arranged as Violet, Indigo, Blue, Green, Yellow, Orange and Red from down to up. When these passes from the second prism, all join together and gives a white light as shown in the figure.

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