Question

A concave mirror forms a real image of an object placed in front of it at a distance $30cm$, of size three times the size of object. Find (a) the focal length of mirror (b) position of image

Answer 1

• $u=-30cm$ and magnification $m=(-v/u)=-3$ so $v=\left(3u\right)$
• image is real so $m$ should be $negative$ $v$ should be negative so $v=-90cm$

putting the above values of $v$ and $u$ in the $Mirror$ equation,

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

we get focal length $f=-22.5cm$ and image position $v=-90cm$