An engineer monitors a straight section of a direct-current supply cable in a service tunnel. The cable runs horizontally in a north–south direction.
Two probes show only the direction of the magnetic field produced by the cable. Probe P is directly above the cable. Probe Q is directly east of the cable and at the same height as the cable.
At first, probe P shows that the magnetic field directly above the cable points west.
The current in the cable is then reversed.
Determine the direction of the conventional current in the cable after it is reversed and the direction of the magnetic field at probe Q.
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.