Question

A concave mirror forms a virtual image of size twice that of the object placed at a distance 5 cm from it. Find:
(a) the focal length of the mirror(b) position of image.

Answer 1

$h_i=2h_o$

$m=2=\frac{h_i}{h_o}=\frac{-v}{u}$

therefore, $v=-2u$

As u=-5cm (given)

so $v=10cm$

now using mirror formula, we have

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

$\frac{1}{f}=\frac{1}{2u}$

$f=10cm$