Question

A convex lens of focal length 10cm forms a virtual image at 30cm from the lens. Find the position of the object from the lens.

• A. 10cm
• B. 8cm
• C. 7.5cm
• D. 75cm

Answer 1

The correct option is C 7.5cm

$v=-30cmf=+10cmu=?\text{So from lens formula}\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\text{We get,}\frac{1}{-30}-\frac{1}{u}=\frac{1}{10}or\frac{1}{u}=\frac{-1}{10}-\frac{1}{30}\Rightarrow \frac{1}{u}=-\frac{4}{30}oru=-7.5cm\text{So, the object must be placed in front}\text{of the lens at a distance of 7.5 cm}\text{from it.}$