# 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

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(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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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.

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