Questions 4 and 5 refer to two small positively charged spheres S1 and S2 suspended by threads,
5 The electrostatic force between the two charges is initially F.
The charge on S1 is doubled whilst the charge on S2 is unchanged. The distance between S1 and S2 doubles. Which of the following is the new force on S2?
The distance between a proton and an electron is r. The electrostatic force is F.
The distance between the proton and electron is doubled.
Which of the following is equal to the electrostatic force at this separation?
Which row of the table gives the force on each charge?
Motors usually have a rotating component which can do work W.
In the diagram below, electric field lines have been drawn around one pair of these spheres.
Add to the diagram to show • the directions of the field lines • the lines of equipotential.
The distance between the centres of each charged sphere in this pair is 5.0 cm.
Show that the force between this pair of charged spheres is about 0.04 N.
charge on each sphere = 0.10 μC
The table shows the typical power and the corresponding angular velocity required for three different appliances.
| Power / W | Angular velocity / rad s–1 | |
| Electric car | 2.0 × 104 | 300 |
| Vacuum cleaner | 1.4 × 103 | 1000 |
| Small pond pump | 0.5 | 200 |
Deduce which of these appliances, in principle, could use the electrostatic motor in (b).
You should use the word equation in (a) and assume that the length of the rod in the electrostatic motor is 8.0 cm.
Assume that the electrostatic motor would deliver a constant force throughout one complete rotation.
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