Question

An object is placed at a distance of 10 cm from a concave lens of focal length 15 cm. Find the magnification produced by the lens.

• A. 3
• B. -3
• C. 0.6
• D. -0.6

Answer 1

The correct option is C 0.6

Since it is a concave lens,
$f=-15\text{cm}$
Object distance, $u=-10\text{cm}$
Using the lens formula,
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
$\Rightarrow \frac{1}{v}-\frac{1}{-10}=\frac{1}{-15}$
$\Rightarrow \frac{1}{v}=-\frac{1}{10}-\frac{1}{15}$
$\Rightarrow \frac{1}{v}=-\frac{1}{6}$
$\Rightarrow v=-6\text{cm}$
Magnification, $m=\frac{v}{u}=\frac{-6}{-10}=0.6$