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 at a distance of

Question

Dr. Abubacker · Accepted Answer

(b) Given that, focal length of a convex lens $f$ = 10 cm, since the lens is used as magnifier, so the object is placed between focal point and lens and image is formed towards the object so
$v\  = \  - \ 25\ cm$
From lens formula
$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
$\Longrightarrow \frac{1}{10} = \frac{1}{- 25} - \frac{1}{u}$
$\frac{1}{u} = \  - \frac{1}{25} - \frac{1}{10} = \  - \frac{7}{50}$
$\Longrightarrow u = \  - \frac{50}{7}cm = \  - 7.14\ cm$

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 at a distance of

Explanation

Reviewed by Dr. Abubacker

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