Question

A person wants a real image of his own , 3 times enlarged. Where should he stand infront of a con cave mirror of radius of curvature 30 cm?

• A. 90 cm
• B. 10 cm
• C. 20 cm
• D. 30 cm

Answer 1

The correct option is C

20 cm

$m=-3,f=\frac{R}{2}=-\frac{30}{2}=-15cm$

$m=\frac{-v}{u}$

$\Rightarrow -3=\frac{-v}{u}\Rightarrow v=3u$

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

putting the values we get,

$\frac{1}{u}+\frac{1}{3u}=\frac{-1}{15}$

$u=-20cm$