A manufacturer tests two drums that rotate against the same dry rubber pad. Each drum is in contact with a copper axle supported by insulating bearings.
Each drum starts neutral and makes the same number of rotations. The mean charge on each drum is measured immediately afterwards.
| Drum material | Copper axle connected to earth | Mean charge on drum in nC\text{nC}nC |
|---|---|---|
| polythene | no | -8.1 |
| polythene | yes | -7.7 |
| aluminium | no | +6.5 |
| aluminium | yes | 0.0 |
Explain the pattern in the results.
Describe the arrangement the manufacturer should use to prevent charge building up on a drum. Your answer should include the direction in which electrons move when the chosen drum is connected to earth.
91 exam-style questions on Edexcel GCSE Physics 11.1 Charging by friction, covering 11.1.1 Charging insulators by friction, 11.1.2 Forces between charges, 11.1.3 Electrostatic phenomena, and 11.1.4 Earthing and removing charge. Each one has a worked solution and a mark scheme showing where the marks go.