Question

A flower is placed 12.0 cm in front of a mirror. If an image of the flower is formed 3.0 cm in front of the
mirror, what kind of mirror is it and what is the focal length of the mirror?

Answer 1

The mirror is a concave mirror.

$\frac {1}{f}=\frac {1}{d_o}+\frac {1}{d_i}$

d_o=12cm, d_i=-3cm

$\frac {1}{f}=\frac {1}{12}+\frac {1}{-3}$

$\frac {1}{f}=-\frac {1}{4}$

f=-4cm