Question

A converging lens of focal length 10 cm forms an image two times magnified image. Calculate position (s) of the object.

Answer 1

Since $m=2$

focal length $=10cm$

$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\to$

$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

Multiply by $u$ on both side;

$\frac{u}{v}-1=\frac{u}{f}$

$\frac{1}{2}=\frac{1}{m}=\frac{u}{v}=\frac{u+f}{f}$

$2=\frac{f}{f+u}$

$\Rightarrow u=-15cm$