Question

An object is placed at a distance of 40 cm from a thin converging lens of focal length 10 cm. The image distance is .

• A. $\frac{50}{3}cm$
• B. $\frac{40}{3}cm$
• C. $\frac{60}{3}cm$
• D. $\frac{20}{3}cm$

Answer 1

The correct option is B $\frac{40}{3}cm$

Given:
Object distance,$u=-40cm$
Focal Length, $f=10cm$
(According to new cartesian sign convention)

Using lens formula, we get
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
$\frac{1}{v}-\frac{1}{(-40)}=\frac{1}{10}$
$v=\frac{40}{3}cm$