## Illustration 27.2: Earth's Magnetic Field

 show:     field vectors     field Lines

This Illustration demonstrates the magnetic field of Earth.  We describe the magnetic field by mapping out magnetic field vectors and/or magnetic field lines.  This Illustration allows you to try both representations.  What is the difference between the two representations?  Restart.

Before adding either field vectors or field lines, add a compass and move it around.  A compass utilizes a small permanent magnet; its arrow points toward the north pole of its magnet.  Now show the field vectors.  Notice that the compass arrow lines up with the field vectors.  The field vectors essentially tell you where little compass needles would point at different places.  Now show the field lines.  On the field-line representation, notice that the compass needle is always tangent to the field line.

Now show the geographic poles of Earth.  Move the compass around (again the compass is a little magnet with the arrow on its north pole).  Is the geographic north pole also the magnetic north pole?   Check your answer by showing the magnetic poles.

Why do you think we call the pole in the Arctic the North Pole?  This is because the north pole of a compass points there (even though by this definition the North Pole is a south pole).  Although we know where the poles are on Earth at the present time, over thousands of years the magnetic north and south poles have flipped back and forth, and we do not yet have a satisfactory theory that explains what causes Earth's magnetic field.

Illustration authored by Morten Brydensholt and modified by Anne J. Cox.
© 2004 by Prentice-Hall, Inc. A Pearson Company