# A spherical mirror and a thin spherical lens have each a focal length of -15 cm. Themirror 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.

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$(a)$ both concave

Explanation:

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.

Conclusion$\rightarrow$
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