Question

The following graph depicts the inverse of magnification versus the distance between the object and lens data for a setup. The focal length of the lens used in the setup is

• A. 250 m
• B. 0.004 m
• C. 125 m
• D. 0.002 m

Answer 1

Answer: (B)

Magnification $(m)=+\frac{v}{u}$
From lens formula,
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
$\Rightarrow \frac{u}{v}-1=\frac{u}{f}$
$\Rightarrow \frac{u}{v}=\frac{u}{f}+1$
$\therefore$ graph between $\left(\frac{u}{v}\right)$
[inverse of magnification] and u will be straight line with slope $\frac{1}{f}$
From graph, slope $=250$
$\therefore f=\frac{1}{250}m=0.004m$