Question

A point object is placed at a distance of 30 cm from a convex mirror of focal length 30 cm. The image will form at

• A. infinity
• B. 15 cm infront of the mirror
• C. 20 cm infront of the mirror
• D. 15 cm behind the mirror

Answer 1

The correct option is D

15 cm behind the mirror

Given, object distance, $u=-30cm$ and focal length, $f=+30cm$.
Let image distance be $v$
Using mirror formula
$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}\Rightarrow \frac{1}{+30}=\frac{1}{v}+\frac{1}{(-30)}$
On solving we get, $v=15cm$, behind the mirror