Question

A concave mirror forms an inverted image of an object placed at a distance of 12 cm from it. The size of the image is double that of the object. Where is the image formed?

Answer 1

Image is inverted so magnification ratio should be negative.

Since the object size is double so magnification ratio $m=-2$

now the object distance from mirror $u=-12$

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

$-2=-\frac{v}{-12}$

$v=-24cm$

image is formed at 24 cm from mirror in same direction of object.

Now be know

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

$\frac{1}{f}=\frac{1}{-24}+\frac{1}{-12}$

$f=-8cm$