Question

A person stands straight infront of a convex mirror at a distance of 30 m away from it. He sees his erect image whose height is $\frac{1}{6}$th of his real height. Find the focal length of the convex mirror.

Answer 1

So the image is $1/6$ of the original height.

u is distance of object from mirror, u=-30 cm

Magnification $m=\frac{1}{6}=-\frac{v}{-30}$

$v=5$ vm

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

$\frac{1}{f}=\frac{1}{5}+\frac{1}{-30}$

$f=6cm$