Question

An object is placed at 60 cm from the pole of a concave mirror whose focal length is 20 cm.
(i) Find the image distance.​

• A. 60 cm
• B. 15 cm
• C. 30 cm
• D. 20 cm

Answer 1

The correct option is C 30 cm

Given :
Focal length, $f=-20cm$
Object distance, $u=-60cm$

Using mirror formula,
$\frac{1}{\text{f}}=\frac{1}{\text{v}}+\frac{1}{\text{u}}$
$\frac{1}{\text{-20}}=\frac{1}{\text{v}}+\frac{1}{\text{-60}}$
$v=-30cm$
Hence, the image distance (v) is - 30 cm from the pole of the mirror.
The correct option is option C.