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Question

# An object is placed at a distance of 30 cm from a convex mirror. The distance of the image formed is 10 cm from the mirror. Calculate the focal length of the mirror.

A
15 cm
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B
15 cm
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C
7.5 cm
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D
7.5 cm
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Solution

## The correct option is A 15 cmGiven, Object distance, u=−30 cm (using sign convention) Image distance, v=+10 cm (using sign convention - image formed by a convex mirror is always virtual, hence, it is behind the mirror) We know, 1f=1u+1v, where f is the focal length 1f=1−30+110 Solving this, we get, f=15 cm Therefore, the focal length of the given convex mirror is 15 cm.

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