Iron filings around a high current vertical wire on OHP to show field.

Iron filings around a high current vertical wire on OHP to show field. Closing a reversing-switch sends a large current (on the order of 400 amps) through a thick copper wire, creating a circular magnetic field with the wire as its axis (determined by the right-hand rule). The wire runs through a glass plate. Medium-coarse iron filings are sprinkled onto the glass near the wire. The filings form circular patterns which are visible when projected on a screen. NOTE: It is important to leave the switch closed for no more than 20 seconds, or the apparatus will melt. 10 seconds would be better. We have had fires. (There is a timer box that buzzes to let you know time is up!)