The small compasses that we use in lab are placed near strong magnetic fields during the Lenz's Law and Magnetism experiments. Frequently this causes the polarity of the compass to flip, resulting in student confusion when trying to determine the north pole of an 'unknown' magnet. The compass can be easily realigned using the following procedure:
Determine if the orientation of a compass is reversed: use a known magnet for identification, recalling that B points away from the north pole of a magnet.	Backwards compass; bump on magnet is north, so the needle should point away from the pole
Assemble the ETP Magnetizer (non-Major's stockroom, shelf JJ4). Place two old steel magnets and an iron keeper in the magnetizer; the polarity of the steel magnets doesn't matter.	Magnetizer with two steel magnets & keeper bar
Turn the magnetizer on, and hold a compass on the outside of one of the steel magnets as shown. Note that you can hold two compasses together on one side, and have a colleague hold two more on the opposite side of the other magnet.	Backwards compass held in place for repair; Note that compass needle points down. Scaly skin optional
Press the black button for a couple of seconds; the compass will spin around and its polarity will be changed!	Compass after repair; note that the compass needle now points upward!
Check the polarity of the repaired compass with the known magnet. Note that you can reverse the polarity of any compass, whether its orientation is correct or reversed!	Repaired compass correctly points away from the north pole

©	St. Lawrence University	Department of Physics

Revised: 09 Nov 18

Canton, NY 13617