During a test, a section of metal ventilation duct is suspended by dry nylon straps. The duct section is given an electric charge.
The charge on the duct section does not change during the 10 seconds before a connection is made.
The table shows the results of three tests. A new charge is given to the duct section before each test.
| Test | Initial charge on duct section | Material joining duct section to Earth | Charge 10 seconds after connection |
|---|---|---|---|
| 1 | +15 nC+15\ \text{nC}+15 nC | copper cable | 0 nC0\ \text{nC}0 nC |
| 2 | −12 nC-12\ \text{nC}−12 nC | copper cable | 0 nC0\ \text{nC}0 nC |
| 3 | −12 nC-12\ \text{nC}−12 nC | dry rubber cord | −12 nC-12\ \text{nC}−12 nC |
A technician concludes that electrons move from the duct section to Earth whenever a copper cable is connected. Assess this conclusion using the results of tests 1 and 2.
In test 1, explain why electron flow stops at the final charge shown in the table.
Tests 2 and 3 have the same initial charge but use different materials to connect the duct section to Earth. What conclusion can be drawn from comparing these tests? Explain your answer.
The duct section is replaced by a plastic sheet. A negative charge is spread over several separate areas of the sheet.
A copper cable touches a point within one negatively charged area, away from the other charged areas, and is connected to Earth.
Describe what happens to the charge at the contact point and to the charge elsewhere on the sheet. Explain your answer.
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.