Question

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 ______.

Options

• both concave

• both convex

• the mirror is concave and the lens is convex

• the mirror is convex, but the lens is concave

Answer 1

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 both concave. 

Explanation:

By convention, the focal length of a concave mirror and the focal length of a concave lens are taken as negative. Hence, both the spherical mirror and the thin spherical lens are concave in nature.