A spherical mirror and a thin spherical lens have each a focal length of –15cm. The mirror and the lens are likely to be

(a) both concave.

(b) both convex.



(a) both concave.



For mirror, 

Concave mirror has its focus on the left.

So, focal length of concave mirror is negative


For lens,

We take focal length of concave lens as negative


Thus, focal length of both Concave mirror and Concave Lens is negative

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CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo