Wisconsin Science MuseumWisconsin Science MuseumIn 1820, Hans Christian Orsted turned on an electric current during an electrical demonstration and noticed that the needle of a nearby compass moved. He had just made one of the most important discoveries in the history of electricity. An electric current causes magnetism. Electromagnetism is used to operate electric motors, one of the most important uses of electrical energy.
Orsted’s discovery was accidental. His compass happened to be near a demonstration using electric current. After his initial accidental observation, he positioned his compass carefully for additional observations.
To do this at home, any piece of metal wire can be used. Copper or aluminum are best. Even a narrow strip of aluminum foil will work. The compass will be attracted to steel wire in the absence of an electric current, so steel wire may not work as well. A D-cell is shown in the pictures, but an AA-cell will work also. A triple A cell will probably work. The demonstration draws quite a bit of current, so it could deplete a smaller battery pretty quickly.
The wire in the picture is an old piece of lamp cord that has deteriorated to the point hat it is no longer safe for it’s original use. It is fine for use in this demonstration. The cord has two conductors, but only one is needed, so the ends of the wire have been twisted together to avoid having to figure out which is which. The insulation at the ends of the cord has been scraped off with a knife.
Put the compass over the wire or foil so that the wire matches the direction of the compass needle.
Connect the ends of the wire to the ends of the battery and watch the compass needle change!
It works best if you stand the battery on top of one end of the wire so you only have to hold the top end. Be careful, it may get hot if you hold the wire for too long!
When current runs through the wire, a magnetic field surrounds the wire, which changes the direction of the compass. The compass needle would point at a right angle to the wire if not for the effect of the earth’s magnetic field. A higher current in the wire would make the needle angle closer to a right angle with the wire.