Question

An object is placed at a distance $20cm$ from the pole of a convex mirror of focal length $20cm$. The image is produced at:

• A. Infinity
• B. $20cm$
• C. $25cm$
• D. $10cm$

Answer 1

Answer: (D)

$10cm$

$u=-20cm,f=20cm$
From mirror formula,
$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$
$\frac{1}{20}=\frac{1}{v}+\frac{1}{-20}$
$\frac{1}{v}=\frac{1}{20}+\frac{1}{20}$
$\frac{1}{v}=\frac{2}{20}\Rightarrow v=10cm$