An engineer tests a magnetic-field sensor using a long straight direct-current cable laid horizontally on a level bench. The cable runs from south to north. The sensor is held directly above the cable and records only the magnetic field produced by the cable.
In each test, the current flows towards the north.
| Test | Current in cable (A) | Distance above cable (cm) | Magnetic field strength (µT) |
|---|---|---|---|
| 1 | 10 | 2 | 100 |
| 2 | 10 | 4 | 50 |
| 3 | 20 | 4 | 100 |
Describe two conclusions about the magnetic field that can be drawn from the results.
The sensor is kept 4 cm above the cable. The current is changed to 20 A towards the south.
Give the strength and compass direction of the magnetic field at the sensor.
90 exam-style questions on AQA GCSE Physics 7.2 The motor effect, covering 7.2.1 Electromagnetism, 7.2.2 Fleming's left-hand rule (HT only), 7.2.3 Electric motors (HT only), and 7.2.4 Loudspeakers (HT only). Each one has a worked solution and a mark scheme showing where the marks go.