$A$ prism of crown glass with a prism angle of $9^{\circ}$ and a prism of flint glass are used to make a direct vision spectroscope. If the refractive indices of crown and flint glass are $1.40$ and $1.60$ respectively,then the refracting angle of the flint glass prism will be.....$^{\circ}$

$A$ small-angled prism is made of a material of refractive index $\frac{3}{2}$. The ratio of the angles of minimum deviation when the prism is placed in air and in water of refractive index $\frac{4}{3}$ is:

$A$ combination of two prisms,one of flint glass and the other of crown glass,produces dispersion without deviation. The angle of the flint glass prism is $15^\circ$. The net angular dispersion for red and violet light will be ..... (Given: for crown glass $\mu = 1.52, \omega = 0.02$; for flint glass $\mu = 1.65, \omega = 0.03$). (in $^\circ$)

The graph between the angle of deviation $(\delta)$ and the angle of incidence $(i)$ for a triangular prism can be represented by:

The angle of deviation through a prism is minimum when
$(A)$ Incident ray and emergent ray are symmetric to the prism
$(B)$ The refracted ray inside the prism becomes parallel to its base
$(C)$ Angle of incidence is equal to that of the angle of emergence
$(D)$ When angle of emergence is double the angle of incidence
Choose the correct answer from the options given below

The angle of an equilateral prism is $60^o$. What should be the refractive index of the prism so that the ray is parallel to the base inside the prism?