Question

A concave mirror for face viewing has a focal length of $0.4 \, m$ . The distance at which you hold the mirror from your face in order to see your image upright with a magnification of $5$ is

• A. $1.60 \, m$
• B. $0.16 \, m$
• C. $0.32 \, m$
• D. $0.24 \, m$

Answer 1

Answer: (C)

$m=5=-\frac{v}{u}\Rightarrow v=-5u$
$f=-0.4 \, m$
From mirror formula,
$\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$
$\frac{1}{- 5 u}+\frac{1}{u}=\frac{1}{- 0 .4}$
$\frac{- 1 + 5}{5 u}=\frac{1}{- 0 .4}$
$u=\frac{4}{5}\left(- 0 .4\right)=-0.32 \, m$
So, distance of object from mirror $=0.32 \, m$