Question

A man uses a concave mirror for shaving.He keeps his face at a distance of 20 cm from the mirror and gets an image which is 1.5 times enlarged. Find the focal length of the mirror.

Answer 1

Focal length ,F = ?

object distance is = -20cm

Magnification $,1.5=\frac{-V}{-20}$

$V=30cm$

using the mirror formula

$\frac{1}{V}+\frac{1}{u}=\frac{1}{F}$

$\frac{1}{30}-\frac{1}{20}=\frac{1}{F}$

$\frac{2-3}{60}=\frac{1}{F}=F=-60cm$