An object is placed at a distance of 40 cm from a concave mirror of… | NEET 2018

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Reflection & Mirrors

An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm. If the object is displaced through a distance of 20 cm towards the mirror, the displacement of the image will be

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Answer: (b)

$f = -15\text{ cm}$ . For $u = -40$ : $\frac{1}{v} = -\frac{1}{15} + \frac{1}{40} = -\frac{1}{24} \Rightarrow v = -24\text{ cm}$
For $u = -20$ : $\frac{1}{v} = -\frac{1}{15} + \frac{1}{20} = -\frac{1}{60} \Rightarrow v = -60\text{ cm}$
The image shifts from 24 cm to 60 cm: $60 - 24 = 36\text{ cm}$ away from the mirror.
So the answer is (b).

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