Find the focal length of the given mirror.

– 30 cm

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– 20 cm

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+ 20 cm

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+ 30 cm

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Solution

The correct option is B – 20 cm
Given,
Object distance, $u = - 60 c m$
Image distance, $v = - 30 c m$

Using mirror formula,
$\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$
$\frac{1}{- 30} + \frac{1}{- 60} = \frac{1}{f}$
$f = - 20 c m$

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Similar questions

A concave mirror has a focal length of 20 cm. Find the position or positions of an object for which the image-size is double of the object size.

An object is placed at 60 cm from the pole of a concave mirror, whose focal length is 20 cm. Find the distance at which the image is formed.

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