The refracting angle of a prism is A, and refractive index of the material of the prism is cot (A/2). The angle of minimum deviation is

If the focal length of objective lens is increased then magnifying power of

The angle of a prism is A. One of its refracting surfaces is silvered. Light rays falling at an angle of incidence 2 A on the first surface returns back through the same path after suffering reflection at the silvered surface.

The refractive index $$\mu $$, of the prism is

Two plane mirrors are inclined at 70^o. A ray incident on one mirror at angle, $$\theta $$ after reflection falls on second mirror and is reflected from there parallel to first mirror. The value of $$\theta $$ is