Question

A student is performing an experiment to determine focal length of a convex lens by using lens formula i.e., by no parallax method. The examiner gives some instructions to the student. The student responds to each instruction as per her understanding of the experiment.

State whether the student's response is correct or incorrect. Give a reason for your answer.

1. EXAMINER: Image formed by the lens is magnified. Reduce the size of the image.
   STUDENT moves the lens towards the object pin.

2. EXAMINER: Plot a graph of (1/v) against (1/u).
   STUDENT takes (1/v) on Y axis and (1/u) on X axis.

3. EXAMINER: Write the relation between the optical power (P) and the focal length (f) of the convex lens.
   STUDENT writes P = 2f.

Answer 1

1. The response of the student is incorrect because the image gets magnified, and the object distance decreases when the lens is moved in the direction of the object pin.
2. Since a graph can only have two axes at most, the student's response is correct.
3. The response of the student is incorrect because the relation between P and f is P = `1/f`.