Question

A convex lens of focal length 15 cm produces a virtual image at a distance of 30 cm from the lens. The object distance is

• A. $5cm$
• B. $7.5cm$
• C. $-10cm$
• D. $10cm$

Answer 1

The correct option is C $-10cm$

All symbols used have their usual meanings.

$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

$\frac{1}{-30}-\frac{1}{u}=\frac{1}{15}$

$\frac{1}{u}=\frac{-1}{30}-\frac{1}{15}$

$u=-10cm$