Magnetic Induction

If you have ever used a magnetic compass, you know that the compass points to the north. In fact, the compass doesn’t point exactly to the North Pole, but to a location called the Magnetic North Pole. The Magnetic North Pole actually moves around the arctic a fair amount. Currently it is located in the Arctic Ocean at a latitude of 86° N and a longitude of 164° E.

Most geophysicists think that Earth’s magnetic field is produced by currents of molten metal in Earth’s outer core. The field is produced by the net movement of charged particles, or ions, in these currents. This is an example of magnetic induction, in which a magnetic field is produced that is perpendicular to an electrical current. In other words, Earth’s outer core acts as an enormous electromagnet.

Students can learn the basics of this process using the Magnetic Induction Gizmo. In the Gizmo, students look down on a table that is pierced by a current-carrying wire that is perpendicular to the table. They can adjust the direction and amplitude of the current, and then visualize the resulting magnetic field by placing magnetic compasses on the table. Students will demonstrate the right-hand rule for determining the direction of the magnetic field and derive an equation for the strength of the field based on the current and distance.