$A$ ray of light passing through an equilateral prism has a velocity of $2.12 \times 10^8 \text{ m/s}$ in the prism material. The minimum angle of deviation is . . . . . . degrees.

$A$ ray of light passes through an equilateral prism such that the angle of incidence $(i)$ is equal to the angle of emergence $(e)$. The angle of emergence is equal to $\left(\frac{3}{4}\right)$ of the angle of the prism. The angle of deviation is: (in $^{\circ}$)

If $r_1$ and $r_2$ are the angles of refraction at the first and second faces of a prism,respectively,then the angle of the prism is:

In the diagram,the ray passing through the prism is parallel to the base. The refractive index of the material of the prism is:

$A$ prism $ABC$ of angle $30^\circ$ has its face $AC$ silvered. $A$ ray of light incident at an angle of $45^\circ$ at the face $AB$ retraces its path after refraction at face $AB$ and reflection at face $AC$. The refractive index of the material of the prism is

Three thin prisms are combined as shown in the figure. The refractive indices of the crown glass for red,yellow,and violet rays are ${\mu _r}, {\mu _y}$ and ${\mu _v}$ respectively,and those for the flint glass are ${\mu _r}', {\mu _y}'$ and ${\mu _v}'$ respectively. If there is no net deviation in the yellow ray,then the ratio $A'/A$ will be: