Topic 10. Electricity and Magnetism
A current flowing in a wire produces a magnetic field around the wire. We can detect this by placing a compass below the wire, as in the photographs.
The wire is horizontal, running in a north-south direction. When the current is off (Figure 10.1), the compass needle aligns itself with the Earth’s magnetic field, and comes to lie parallel with the wire. When the current is switched on (Figure 10.2) and flowing through the wire from the bottom to the top of the picture, it generates a strong magnetic field, which deflects the compass needle.