Question

A beam of light converges towards a point O, behind a convex mirror of focal length 20 cm. Find the magnification and nature of the image when point O is 30 cm behind the mirror.

• A. 2 (virtual, inverted)
• B. 3 (real, inverted)
• C. 3, (virtual, enlarged)
• D. +1 (real, enlarged)

Answer 1

The correct option is A 2 (virtual, inverted)

$u=30$ ; $f=20$

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

$\frac{1}{v}+\frac{1}{30}=\frac{1}{20}$

$v=60$

Image is virtual (v>0)

Magnification is $-\frac{v}{u}=-\frac{60}{30}=-2$ (<0) hence it is inverted.