This model shows a bar magnet and compass sitting on
a table in a classroom at the latitude of Massachusetts. The interaction between
the magnetic field of the bar magnet and the magnetic
field of the earth is illustrated by the fieldlines
that extend out from the bar magnet. Fieldlines that
emerge towards the edges of the magnet generally reconnect
to the magnet near the opposite pole. However, fieldlines
that emerge near the poles tend to wander off and reconnect
to the magnetic field of the earth, which, in this case,
is approximately a constant field coming at 60 degrees
from the horizontal.
Looking at the compass, one can see that a compass
needle will always align itself in the direction of
the local field. In this case, the local field is dominated
by the bar magnet.
Click and drag the mouse to rotate the scene. Control-click
and drag to zoom in and out.