Physics 9702/51 — May/June 2018

A student is investigating the force between two charged metal spheres S and T, as shown in Fig. 1.1.

Each sphere may be charged by connecting the positive lead from a power supply to the sphere and then removing the lead. The electromotive force (e.m.f.) of the power supply used to charge sphere T is $V$.

The force $F$ between the two charged spheres may be determined by attaching sphere S to a top pan balance.

For a constant charge on sphere S, it is suggested that the relationship between $F$ and $V$ is

where $r$ is the distance between the centres of the spheres and $\alpha$ is a constant.

Design a laboratory experiment to test the relationship between $F$ and $V$.
Explain how your results could be used to determine a value for $\alpha$.

You should draw a diagram, on page 3, showing the arrangement of your equipment. In your account you should pay particular attention to

• the procedure to be followed,
• the measurements to be taken,
• the control of variables,
• the analysis of the data,
• any safety precautions to be taken.