write relation b/w refractive index and wavelength of light .draw graph to show the variation of ref.indx of material with wavelength.for colours:

1> red or yello will the ref. indx be more ?

The relation between refractive index and wavelength of light is given by Cauchy's equation as follows:

Where, A, B, C are constants. Since, wavelength is a very small number of the order of few hundred nano meter we omit the higher powers of λ.

Thus,

The graph for refractive index versus wavelength of light is given below:

From the equation we have,

Refractive index is inversely proportional to the wavelength of light. Wavelength of violet light is around 380 nm to 450 nm and wavelength of red light is around 620 nm to 740 μm. Therefore, refractive index for violet light will be more than the refractive index for red light.

Hence, red light is least dispersed while violet light is most dispersed.