Question

A point light source is kept in front of a convex mirror at a distance of $40cm$. The focal length of the mirror is $40cm$. The image is formed

• A. in front of the mirror at a distance $10cm$
• B. behind the mirror at a distance $10cm$
• C. behind the mirror at a distance $20cm$
• D. in front of the mirror at a distance $20cm$

Answer 1

Answer: (C)

behind the mirror at a distance $20cm$

Given, $u=-40cm$
$f=40cm$
$v=?$
We know
$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$

$\frac{1}{40}=\frac{1}{v}+\frac{(-1)}{40}$

$\frac{1}{v}=\frac{1+1}{40}$

$v=20cm$
Hence, image formed behind the mirror at a distance of $20cm$.