A 16 cm long image of an object is formed by a convex lens on a screen placed normal to its principal axis. On moving the lens towards the screen, without changing the positions of the object and the screen, a 9 cm long image is formed again on the screen. The size of the object is:
Answer & explanation
Correct answer: option 3
$y=\sqrt{y_1 \times y_2}$
$=\sqrt{16 \times 9}$
= 4 × 3 = 12 cm.