What is dispersion of white light? What is the cause of such dispersion? Draw a diagram to show the dispersion of white light by a glass prism.


Prism is a three-dimensional solid object in which the two ends are identical. It is the combination of the flat faces, identical bases and equal cross-sections. The faces of the prism are parallelograms or rectangles without the bases. And the bases of the prism could be triangle, square, rectangle or any n-sided polygon.



Dispersion of white light is defined as splitting of white light into seven constituent colours when passed through the prism. When white light is passed through a glass prism it splits into its spectrum of colours (in order violet, indigo, blue, green, yellow, orange and red) and this process of white light splitting into its constituent colours is termed as dispersion.


When white light is made to pass through a prism, a spectrum of seven colours is formed which shows that white light is a mixture of seven different colours. Prism only acts as a medium for the separation of the seven colours. When light falls on the glass prism, refraction takes place. Since the wavelength of different components of light is different and the frequency is constant, each component gets deviated by a different angle due to the difference in velocity in the glass medium. The red colour having the maximum wavelength deviates the least and forms the upper part of the spectrum whereas violet having the least wavelength deviates the most.

White light dispersion occurs because, as they pass through a prism, different colours of light bend through different angles with respect to the incident ray. The red light bends the least while the violet bends most as shown below.

Dispersion of white light by a glass prism



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