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Question

An object kept at 20 cm from a spherical mirror gives rise to an image 15 cm behind the mirror. The focal length of the mirror is:

A
60 cm
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B
30 cm
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C
90 cm
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D
60 cm
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Solution

The correct option is D 60 cm
Given:
Object Distance, u=20 cm
Image Distance, v=+15 cm
( image is formed behind the mirror)

Using Mirror Formula,
1u+1v=1f
120+115=1f
f=+60 cm
Since f is positive, mirror used here is convex mirror.

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