Compare the dispersive powers of two prisms if one of them deviates the blue and red rays through $10^{\circ}$ and $6^{\circ}$ respectively,and the second prism through $8^{\circ}$ and $4.5^{\circ}$.

Dispersive power depends on the following:

The dispersion for a medium of wavelength $\lambda$ is $D$. Then,the dispersion for the wavelength $2\lambda$ will be:

Let us list some of the factors,which could possibly influence the speed of wave propagation:
$(i)$ nature of the source.
$(ii)$ direction of propagation.
$(iii)$ motion of the source and/or observer.
$(iv)$ wavelength.
$(v)$ intensity of the wave.
On which of these factors,if any,does
$(a)$ the speed of light in vacuum,
$(b)$ the speed of light in a medium (say,glass or water),depend?

The focal length of a lens is $20 \ cm$ and its dispersive power is $0.08$. What is its longitudinal chromatic aberration in $cm$?

The refractive index of flint glass for blue $F$ line is $1.6333$ and red $C$ line is $1.6161.$ If the refractive index for yellow $D$ line is $1.622,$ the dispersive power of the glass is