Question

An object is put at a distance of $5cm$ from the first focus of a convex lens of focal length $10cm$. If a real image is formed, its distance from the lens will be :

• A. $15cm$
• B. $20cm$
• C. $25cm$
• D. $30cm$

Answer 1

The correct option is D $30cm$

$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
$\frac{1}{v}-\frac{1}{-15}=\frac{1}{f}$
or $\frac{1}{v}=\frac{1}{-15}+\frac{1}{10}$ or $\frac{1}{v}=\frac{-2+3}{30}$
or $v=30cm$.