Experiment -3
Objective
Find the focal length of convex lens by plotting a graph between u and v.
Formula Used
Where,
f = focal length of convex lens.
u = distance of object needle from optical centre of lens.
v = distance of image needle from optical centre of lens.
Note:- According to sign convention u has -ve value and v has +ve value, hence f comes +ve .
Ray Diagram
Rough focal length =20 cm
Observation table
Result
From graph, focal length of convex lens is 20cm.
Precautions
- The tips of the needles and the center of the lens should be at the same height.
- Parallax must be removed tip to tip.
- The index correction should be taken into account.
- The uprights carrying the lens and the needles should not be shaky.
Sources of error
- The needles are not at the same height.
- Index correction not properly applied.
- Parallax not removed.
Section B – Experiment 2 | Section B – Experiment 4 |