E.3.3 Magnetic Field of a Bar Magnet

A compass table with a hundred or so tiny compass needles displays the magnetic field of a bar magnet, or two attracting or repeling magnets, for overhead projection. The compass table replaces the old iron filing magnetic field demonstrations (which are still available).

Compass tables are also used to show the magnetic fields of a long straight wire, a solenoid coil, and a current loop, E.4.3 and E.4.4. The "magniprobe" is a tiny bar magnet completely free to rotate on gimbals in any direction. It will display the three dimensional form of the magnetic field of a bar magnet, delighting the instructor. However, the device is too small to be seen by more than a few students at once unless enlarged on TV. The "Mark II" version of the magniprobe is sensitive enough to detect the earth's field.