A biconvex lnes is to be made from glass of refractive index 1.5, with both faces having some radius of curvature. Determine the focal length if this radius of curvature is 30 cm.

A biconvex lens is to be made form glass of refractive index 1.55, which both faces having same radius of curvature. Determine this radius of curvature if the focal length is 20 cm.

A 60^@ prism made of glass of refractive index 1.5. Find the angle of minimum deviation.