Question

An object is placed at a distance of 30 cm. from a concave mirror. The magnification produced is $1/2$. where should the object be placed to get the magnification of 1/3.

Answer 1

$U=-30$

$m=\frac{1}{2}$

we know that

$m=\frac{-V}{U}$

so V = 15

$f=10$

for $m=\frac{1}{3}$

$\frac{-V}{U}=\frac{1}{3}$

$V=\frac{-V}{3}$

$\frac{1}{f}=\frac{1}{V}+\frac{1}{U}$

$\frac{1}{10}=\frac{3}{-U}+\frac{1}{U}$

U = -40

Therefore for magnification to be $\frac{1}{3}$ the object must be placed 40cm upon in front of the mirror.