A spherical mirror and a thin spherical lens have each a focal length of −15 cm. The mirror and the lens are likely to be (a) both concave (b) both convex (c) the mirror is concave and the lens is convex (d) the mirror is convex, but the lens is concave
Option (a) By convention, the focal length of a concave mirror and a concave lens are taken as negative. Hence, both the spherical mirror and the thin spherical lens are concave in nature.
