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

A plano convex lens fits exactly into a plano concave lens. Their plane surfaces are parallel to each other. If lenses are made of different materials of refractive indices $$\mu $$₁ and $$\mu $$₂ and R is the radius of curvature of the curved surface of the lenses, then the focal length of the combination is

For a normal eye, the cornea of eye provides a converging power of 40 D and the least converging power of the eye lens behinf the cornea is 20 D. Using this information, the distance between the retina and the cornea-eye lens can be estimated to be

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.