Permalloy has a high magnetic
permeability
in weak fields. Hold the rod parallel to the earth's field
and the lower end will attract the south end of the compass needle and
repel the north, provided it doesn't get so close that the compass
magnetizes
the rod. Reverse the rod and its poles reverse.
Use the transparent tray of iron
filings on
the overhead projector to show that the filings stick to rod when it is
oriented parallel to earth's field and fall off when the rod is
perpendicular
to the field.
