$A$ light ray is incident on a prism of prism angle $60^{\circ}$ such that it undergoes minimum deviation. If the refractive index of the prism is $\sqrt{2}$,then the angle of incidence is .......$^{\circ}$.

$A$ ray of light incident on one face of an equilateral glass prism having refractive index $\sqrt{2}$, produces the emergent ray which just grazes along the adjacent face. The value of angle of incidence is $(\sin 90^{\circ} = 1, \sin 30^{\circ} = 0.5, \sin 45^{\circ} = 1/\sqrt{2})$.

For the angle of minimum deviation of a prism to be equal to its refracting angle,the prism must be made of a material whose refractive index

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.

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.

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