Question

An object is present on the principal axis of a concave mirror at a distance 30 cm from it. Focal length of mirror is 20 cm. Image formed by mirror is :

• A. at a distance 60 cm in front of mirror
• B. at a distance 60 cm behind the mirror
• C. at a distance 12 cm in front of mirror
• D. at a distance 12 cm behind the mirror

Answer 1

The correct option is A at a distance 60 cm in front of mirror

Object distance $u=-30$ cm

Focal length of the mirror $f=-20$ cm

Using mirror formula $\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$

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

$⟹v=\frac{\left(30\right)\left(20\right)}{-30+20}=-60$ cm

Since image distance comes out to be negative, thus image is formed in front of the mirror at a distance of $60$ cm.