TO MEASURE THE FOCAL LENGTH OF A CONVEX LENS.

In an experiment to measure the focal length, f, of a convex lens, the values for u, the object distance, and v, the image distance, were as follows:

u / cm	14	15.5	17	18.5	20	21.5	23
v / cm	35.0	28.2	24.3	21.8	20.0	18.7	17.7

Use these values to find a single value for f.

SOLUTION

Change to metres:

u / m	0.140	0.155	0.170	0.185	0.200	0.215	0.230
v / m	0.350	0.282	0.243	0.218	0.200	0.187	0.177

We now wish to graph 1/u against 1/v.

1/u / m^-1	7.1	6.5	5.9	5.4	5.0	4.7	4.3
1/v / m^-1	2.9	3.5	4.1	4.6	5.0	5.3	5.7