Dispersion by a Prism

A thin prism $P_1$ with angle $4°$ and made from glass of refractive index $1.54$ is combined with another prism $P_2$, made of glass of refractive index $1.72$ to produce dispersion without deviation. The angle of prism $P_2$ is

If the refractive indices of a prism for red, yellow and violet colours be $1.61$,$1.63$ and $1.65$ respectively, then the dispersive power of the prism will be

Light of wavelength $4000 \stackrel{\circ }{\mathrm{A}}$ is incident at small angle on a prism of apex angle $4°.$ The prism has $n_{\mathrm{v}}=1.5$ and $n_{\mathrm{r}}=1.48$ .The angle of dispersion produced by the prism in this light is

A convex lens has mean focal length of $20 \mathrm{cm}$. The dispersive power of the material of the lens is $0.02$. The longitudinal chromatic aberration for an object at infinity is

The condition for an achromatic doublet is (here $f_1$ and $f_2$ are the focal length and ${\omega }_1 \text{and} {\omega }_2$ are dispersive powers of individual lenses.)

The refractive index for the light of violet and red colour of any material are $1.66$ and $1.64$ respectively. If the angle of prism made of this material is $10°$. Then angular dispersion is