Question

Find the focal length of the given mirror.

• A. + 30 cm
• B. – 20 cm
• C. – 30 cm
• D. + 20 cm

Answer 1

The correct option is B – 20 cm

Given,
Object distance, $u=-60cm$
Image distance, $v=-30cm$

Using mirror formula,
$\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$
$\frac{1}{-30}+\frac{1}{-60}=\frac{1}{f}$
$f=-20cm$