Question

S.No. Object-Distance u (cm) Image-Distance v (cm)
1 -100 +25
2 -60 +30
3 -40 +40
4 -30 +60
5 -25 +100
6 -15 +120

i. What is the focal length of the convex lens? Give reason to justify your answer.
ii. Write the serial number of the observation which is not correct. On what basis have you arrived at this conclusion?

Answer 1

The lens equation says 1/f = 1/Do + 1/Di, where f is the focal length of the lens, Do is the distance from the object to the lens and Di is the distance from the lens to the in-focus projected image.