This is one of the greatest demonstrations in the history of electromagnetism.
Apparatus and materials
Copper wire, PVC-covered, 26 SWG, 50-100 cm with bare ends
Health & Safety and Technical notes
The power supplies used in this experiment must be able to allow a current of up to 10 amps to flow when a short piece of wire is connected across its 1 or 2 volt terminals. Many 0-12 volt power supplies will not pass such high currents and so the trip switch will cut out or, worse still, the power supply will be damaged. Students should be encouraged to switch off the power supply when they are not using it because the wires and coils will become hot.
a Using wire strippers, bare approximately 3 cm of each end of the wire.
b Connect the ends of the wire to the DC terminals (red and black) of the power supply.
c Switch the supply on so a large current flows through the wire.
d Hold the compass above and then below the wire. Observe how it orientates itself in each position.
1 When an electric current is flowing through the wire, compass needles placed above and below the wire will point in opposite directions.
2 How Science Works Extension: Oersted discovered this effect while giving a public demonstration in 1820. For more about this, see Oersted, electric current and magnetism.
This experiment was safety-checked in July 2007