The property of light that explains the formation of coloured images due to thick lenses is

The refractive index of flint glass for blue light is $1.6333$ and for red light is $1.6161$. Calculate the dispersive power of the prism,assuming the mean refractive index is approximately the average of the two given values.

Explain dispersive and non-dispersive medium.

The Cauchy's dispersion formula is:

Consider the four different cases of dispersion of a light ray which has all the wavelengths from ${\lambda _1}$ to ${\lambda _2}$ (where ${\lambda _1} > {\lambda _2}$). The dotted line represents the light ray of wavelength ${\lambda _{avg}}$. Which ray diagram shows the maximum dispersive power?

$A$ medium is said to be dispersive,if