Question

A convex lens of focal length 20 cm forms a real image at 30 cm from the lens. The object distance is:

• A. 60 cm
• B. 12 cm
• C. 15 cm
• D. 10 cm

Hint:

Use lens formula carefully with sign convention.

Answer 1

The Correct Option is A

\[ \frac{1}{f}=\frac{1}{v}+\frac{1}{u} \Rightarrow \frac{1}{20}=\frac{1}{30}+\frac{1}{u} \] \[ \frac{1}{u}=\frac{1}{60}\Rightarrow u=60\ \text{cm} \]