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  4. The focal length of a simple convex lens used as a magnifier is 10 cm . For the image to be formed at a distance of distinct vision D=25 cm , the object must be placed away from the lens nearly at a distance of

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Q. The focal length of a simple convex lens used as a magnifier is $10 \, cm$ . For the image to be formed at a distance of distinct vision $D=25 \, cm$ , the object must be placed away from the lens nearly at a distance of

NTA AbhyasNTA Abhyas 2022

Solution:

$f=+10 \, \text{cm.}$
$v=25 \, \text{cm.}$
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
$\frac{1}{25}-\frac{1}{u}=\frac{1}{10}$
$\frac{10 - 25}{250}=\frac{1}{u}$
$u=16\text{ cm}$