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.

AcademicPhysicsNCERTClass 10

$(a)$ both concave


Let us know some details about the concave mirror and concave lens.

Concave mirror$\rightarrow$
If a hollow sphere is cut into parts and the outer surface of the cut part is painted, then it becomes a mirror with its inner surface as the reflecting surface and is known as a concave mirror. 

Convex lens$\rightarrow$
A concave lens is a lens that diverges a straight light beam from the source to a diminished, upright, virtual image.

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

When a spherical mirror and a spherical lens each have a focal length of, $-15\ cm$, then the mirror and the lens are likely to be concave.

Therefore, option $(a)$ is correct.
Updated on 10-Oct-2022 13:20:00