For a symmetric (equilateral) prism,the prism formula can be written as

For a small angled prism with prism angle $A$,the angle of minimum deviation $(\delta_m)$ varies with the refractive index $(\mu)$ of the prism as shown in the graph.

The angle of a prism is $60^o$ and its refractive index is $\sqrt{2}$. The angle of minimum deviation suffered by a ray of light in passing through it is......$^o$

Assertion: There exist two angles of incidence for the same magnitude of deviation (except for minimum deviation) by a prism kept in air.
Reason: In a prism kept in air,a ray is incident on the first surface and emerges out of the second surface. If another ray is incident on the second surface along the path of the previous emergent ray,then this ray emerges out of the first surface along the path of the previous incident ray. This principle is called the principle of reversibility of light.

One face of a prism with a refracting angle of $30^{\circ}$ is coated with silver. $A$ ray incident on the other face at an angle of $45^{\circ}$ is refracted,reflected from the silver-coated face,and retraces its path. The refractive index of the prism is:

$A$ thin prism of angle $6^{\circ}$ made of glass of refractive index $1.5$ is combined with another prism made of glass of refractive index $1.75$ to produce dispersion without deviation. Then, the angle of the second prism is (in $^{\circ}$)