Question

In the experiment to determine the focal length of a convex lens, using the method of parallex, the following observation were recorded by a student. Which of the observations is possibly not taken correctly by the student?

SI.No.	Position of the object (cm)	Position of Lens (cm)	position of Images (cm)
1.	25	50	66.7
2.	30	50	70.0
3.	35	50	80.0
4.	38	50	88.0
5.	20	50	65.0
6.	15	50	64.0

(1) S. No. 6

(2) S. No. 5

(3) S. No. 4

(4) S. No. 3

Answer 1

(3) S. No. 4

Obtaining the values of u and v for each set and calculating the value f using the formula 1/f = 1/v - 1/u, we get the following table.

Clearly, observation at Sl. No. 4, has not been taken correctly.