Question

Calculate the magnification of an object if it is kept at a distance of $3cm$ from a concave mirror of focal length $4cm$:

• A. $3$
• B. $6$
• C. $9$
• D. $4$

Answer 1

The correct option is D $4$

Given:

Object distance $u=-3cm$

Focal length $f=-4cm$

By mirror formula,

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

$\frac{1}{-3}+\frac{1}{v}=\frac{1}{-4}$

$\frac{1}{v}=\frac{1}{12}$

So, image distance $v=+12cm$

Magnification $m=-\frac{v}{u}$

$=-\frac{+12}{-3}=+4$

Option D is correct.