Oersted's Experiment

Ampere's law - magnetics fields around wires - galvanic current

What it shows:
Oersted showed that an electric current produces a magnetic field. His experiment is repeated here on a suitable grand scale.

How it works:
The current carrying wire in this case is a tubular 18mm diameter pipe 1   of dimensions shown in figure 1. The field is measured at the center of a vertical 1.5m stretch by four compass needles sitting on a Plexiglass platform. With no current, the needles all align themselves with the Earth's magnetic field. Putting 250A through the pipe aligns the needles with the circuital field lines (the direction follows the right hand screw rule).

figure 1. Compass platform and dimensions of wire loop

Setting it up:
The current loop can be clamped upright onto a lecture bench; the base rests on the ground. Current is supplied by a Sorensen 2   DC supply at 250A (the ends of the tube are fitted with high current connectors). The compass needles are 15cm in length. 3   Don't place the compass needles too close to the pipe as it's made of steel.

Comments:
The current should be increased gradually to 250A to limit compass oscillations. Hans Christian Oersted (1777-1851) was the first to find a connection between electricity and magnetism. His demo could be used as one of the stepping stones towards Maxwell's equations. The experiment is repeated on a smaller scale in OHP Magnetic Lines of Force. Rating***


1 the pipe is thin walled steel electrical conduit. Its resistance is high enough so that 250A heats it up. Copper pipe would be better.
2 Sorensen (Raytheon) DCR20-250 power supply
3 Sergent-Welch 1869