Question

A point object is placed at a distance of $30\text{cm}$ from a convex mirror of focal length $30\text{cm}$. The image will be formed at

• A. infinity
• B. $30\text{cm}$ behind the mirror
• C. $15\text{cm}$ infront of the mirror
• D. $15\text{cm}$ behind the mirror

Answer 1

The correct option is D $15\text{cm}$ behind the mirror

Given that
$u=-30\text{cm},f=30\text{cm}$
Using the mirror formula
$\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$
$\frac{1}{v}+\frac{1}{-30}=\frac{1}{30}$
$v=+15\text{cm}$
i.e $15\text{cm}$ behind the mirror

Why this question? Note: For a real object placed infront of convex mirror, image is virtual and diminished.