Question

A convex lens of focal length $10cm$ is placed at a distance of $12cm$ from a wall. How far from the lens should an object be placed so as to form its real image on the wall?

• A. $20cm$
• B. $50cm$
• C. $30cm$
• D. $60cm$

Answer 1

The correct option is D $60cm$

Given:
Image distance, $v=12cm$
Focal length, $f=10cm$ (positive for convex lens)

Let the object distance be $u$. Using the lens formula,
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
$\frac{1}{12}-\frac{1}{u}=\frac{1}{10}$
$u=-60cm$

Thus, the object should be placed at a distance of $60cm$ from the convex lens on the opposite side of the wall.