Q

A convex mirror forms a 2.5 cm image of a 10 cm object at distance 30 cm. What is its focal length?

RRB Group-D 06/10/2022 / Shift-I 2022
✓ Answer: D 10 cm
m = 2.5/10 = 0.25. With u = −30 cm, v = −mu = +7.5 cm. Thus 1/f = 1/7.5 − 1/30 = 1/10.
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