Magnetostatics

Where's North?

Hang identical magnets from string and notice that they all align themselves in the same direction.

Two cultures noticed this phenomenon and used it to build devices to show direction: The Chinese first around 1000 AD and then the Europeans.

Form a standards committee to choose one direction as the one the magnets points toward.

You cannot make a wrong choice here, unlike betamax, the Chinese chose the south direction and the Europeans chose north.

Magnetic Poles

Mark your chosen poles with a dot. Investigate how the dot poles and nodot poles interact with each other and with other substances.

Notice that like poles repel, unlike poles attract, and both types of poles attract some materials and do nothing to others.

Realize that the north pole of the magnet, the one near the star Polaris, points north because the magnetic pole near the north geographic pole is a south magnetic pole.

Magnetic Globe

A squishy earth globe toy contains a neodymium magnet. This allows it to attract and orient used staples on the surface of the globe against the gravity force of the real earth.

Notice that there are two laces where the staples stand up vertically, these are the magnetic poles. There is a line along which they lie flat, this is the magnetic equator. Between the equator and the poles the staples tilt at angles related to the latitude. The further away from the equator the steeper the tilt known as the "dip" or "magnetic inclination."

Historically, William Gilbert did the same thing 400 years ago. He made a sphere out of magnetite and covered it with bits of iron. Year 2000 is the 400'th anniversary of his publication of De Magnete.

The magnetic earth globe was invented by Paul Doherty and Tien Huynh-Dinh.

Notice that you can use a compass to trace the magnetic field out away from the globe. The neodymium magnet inside the globe is stronger than the earth's magnet out to a distance of 25 cm or more.

The earth's magnetic field reaches out far into space. It traps the solar wind creating the Van Allen Radiation Belts. The earth's magnetic field also guides the charged particles from the solar wind to collide with molecules in the earth's atmosphere in the far north and south creating the aurora. See the Exploratorium observatory page on aurora.

 Scientific Explorations with Paul Doherty © 2000 27 July 2000