Question

A convex lens of focal length10 cm is placed at a distance of 12 cm from a wall. How far from the lens should an object be placed so as to form its real image on the wall?

• A. 30 cm
• B. 15 cm
• C. 120 cm
• D. 60 cm

Answer 1

Answer: (D)

60 cm

$f=10cm,v=12cm,u=?$

We know, $\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$
$\frac{1}{10}=\frac{1}{12}-\frac{1}{u}$

$u=-60cm$

$\therefore$The object must be placed at a distance $60cm$ in front of the lens.