Dispersion of White Light by a Glass Prism


How could the white light of the Sun give us various colours of the rainbow?


The prism has probably split the incident white light into a band of colours.

  •  The various colours seen are Violet, Indigo, Blue, Green, Yellow, Orange and Red, as shown in Fig.
  • The acronym VIBGYOR will help you to remember the sequence of colours.
  • The band of the coloured components of a light beam is called its spectrum.
  • The splitting of light into its component colours is called dispersion. Dispersion.
  •  Different colours of light bend through different angles with respect to the incident ray, as they pass through a prism. The red light bends the least while the violet the most.


        Sunlight is made up of Seven Colour:


Isaac Newton was the first to use a glass prism to obtain the spectrum of sunlight. He tried to split the colours of the spectrum of white light further by using another similar prism. However, he could not get any more colours. He then placed a second identical prism in an inverted position with respect to the first prism. Allowed all the colours of the spectrum to pass through the second prism. He found a beam of white light emerging from the other side of the second prism. This observation gave Newton the idea that the sunlight is made up of seven colours.

             How a Rainbow is formed?


          A rainbow is a natural spectrum appearing in the sky after a rain shower.

It is caused by dispersion of sunlight by tiny water droplets, present in the atmosphere.

A rainbow is always formed in a direction opposite to that of the Sun. The water droplets act like small prisms. They refract and disperse the incident sunlight, then reflect it internally, and finally refract it again when it comes out of the raindrop.

Due to the dispersion of light and internal reflection, different colours reach the observer’s eye.