Question

A spherical mirror and a spherical lens each have 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 but the lens is convex.
(d) the mirror is convex but the lens is concave.

Answer 1

(a) Both concave

According to the sign convention, the focal length for both a concave mirror and a concave lens is negative.