question_answer

A thin linear object of size 1 mm is kept along the principal axis of a convex lens of focal length 10 cm. The object is at 15 cm from the lens. The length of the image is:

A) 1 mm

B) 4 mm

C) 2 mm

D) 8 mm

Correct Answer: B

Solution :

[b] \[\frac{1}{10}=\frac{1}{V}=-\frac{1}{(-15)}\Rightarrow v=+30\,cm\] for small object \[dv=\frac{{{v}^{2}}}{{{u}^{2}}}du={{\left( \frac{30}{15} \right)}^{2}}\times 1=4\,mm\]