The splitting up of white light into seven colours on passing through a transparent medium like a glass prism is called dispersion of light.
The dispersion of white light occurs because colours of white light travel at different speeds through the glass prism.
When white light consisting of seven colours falls on a glass prism, each colour in it refracted (or deviated) by a different angle, with the result that seven colours are spread out of form a spectrum.
The deviation in the path of the light is inversely proportional to the wavelength.
Red light suffers the least amount of deviation since it has the highest wavelength and violet is deviated the most since it has the lowest wavelength.
SPECTRUM OF WHITE LIGHT
The band of seven colours formed on a white screen, when a beam of white light is passed through a glass prism, is called spectrum of white light.
It is a beautiful spectrum seen in the sky when the sun shines on raindrops during or after a rain shower.
A rainbow is produced by the dispersion of white sunlight by raindrops (or water drops) in the atmosphere.
The raindrops in the atmosphere act like many small prisms splitting into a spectrum.