Question

A convex lens forms a real image 4 cm long on a screen. When the lens is shifted to a new position without disturbing the object or the screen, again real image is formed on the screen which is 16 cm long. The length of the object is :

• A. 8 cm
• B. 10 cm
• C. 12 cm
• D. 6cm

Answer 1

The correct option is A 8 cm

If the image sizes be $I_{1}and{I}_2$,

By Displacement Method, object size ($OS$) is given by :

$OS=\sqrt{I_1{I}_2}$

Thus, OS = $\sqrt{64}$

$⟹$ $OS=8$