When white light enters a prism, it gets splitted into its constituent colours. This is due to:

CONCEPT:

• The splitting of a composite beam of light into its constituent colours is called dispersion of light.
• The dispersion of white light occurs because the colours of white light travel at different speeds through the glass prism.
• The dispersion was discovered by Sir Issac Newton.
• Newton discovered that light is made up of seven different colours.

EXPLANATION:

• As we know that, the refractive index is defined as the ratio of the speed of light in a vacuum to the medium i.e.,

\({\rm{Refractive\;index\;}}\left( \mu \right) = {\rm{\;\;}}\frac{{Speed\;of\;light\;in\;vaccum\left( C \right)}}{{Speed\;of\;light\;in\;a\;medium\left( v \right)}}\)

• According to Cauchy's formula, refractive index (μ) of a material depends on the wavelength (λ) of light falling on it as

\(\Rightarrow μ = A + \frac{B}{{{\lambda ^2}}} + \frac{C}{{{\lambda ^3}}} + - - - \)

Where A, B, C....... are constants.

• From the above relation, it is clear that the refractive index is inversely proportional to the wavelength of the light used.
• As the refractive index (μ) of the prism is different for different colours, therefore the speed of light will be different for different colors thus, they deviate through different angles on passing through the prism. Hence, they are seen as separate.