Question

An object and screen are fixed at a distance $d$ apart. When a lens of focal length $f$ is moved between the object and the screen, sharp images of the object are formed on the screen for two potions of the lens. The magnifications produced at these two positions are $M_1$ and $M_2$.

• A. $d>2f$
• B. $d>4f$
• C. $M_1{M}_2=1$
• D. $\left|M_1\right|-\left|M_2\right|=1$

Answer 1

Answer: (B), (C)

$d>4f$
$M_1{M}_2=1$

Condition is $d>4f$
and if $u$ is object distance and $d$ is distance between object and screen , then $d-u$ is image distance for image1 and vice versa for image2

$M_1=\frac{d-u}{u}$ ; $M_2=\frac{u}{d-u}$

hence $M_1{M}_2=1$.