A convex lens of focal length $3 c m$ forms a real image at $24 c m$ from its optic centre. Calculate the distance of the object from the lens.

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Solution

Given: Focal length, $f = 3 c m$

Since image formed is real it will be on opposite side of lens hence
Image distance, $v = 24 c m$

To find: $O b j e c t d i s t a n c e, u$

From lens formula,

$\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$

$\frac{1}{24} - \frac{1}{u} = \frac{1}{3}$

$\frac{1}{u} = \frac{1}{24} - \frac{1}{3}$

$u = \frac{- 24}{7} c m$

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