Question

The focal length of a plano-concave lens is -10 cm , then its focal length when its palne surface is polished is

Answer 1

Explanation:

Coating the spherical surface of the lens would get you a convex mirror, but we don't know its focal length. The mirror's focal length depends on its radius of curvature. The focal length of the lens depends both on radius of curvature of the surface and the glass refractive index