Question

A point object at $O$ and a diverging lens is shown in the figure given below. Find the position of final image formed from $P$.

• A. $+10\text{cm}$
• B. $-5\text{cm}$
• C. $+20\text{cm}$
• D. $-15\text{cm}$

Answer 1

The correct option is B $-5\text{cm}$

Sign convention: Direction of incident ray is taken as +ve.
Given that,
Distance of object from optical centre of lens, $u=-10\text{cm}$
Focal length of lens, $f=-10\text{cm}$
Applying lens formula,

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

$\Rightarrow \frac{1}{v}-\frac{1}{(-10)}=\frac{1}{-10}$

$\frac{1}{v}=\frac{-1}{10}-\frac{1}{10}$

$\frac{1}{v}=\frac{-2}{10}$

$\therefore v=-5\text{cm}$