- The science and stories of the "De Magnete" site are quite appropriate for science classes, especially in this anniversary year of 2000. Since no math is involved, they can be presented in a 9th grade Earth Sciences course, and even to younger students. The main points stressed would be
- Permanent magnetism and the magnetism of the Earth.
- Magnetism caused by electric currents
- Sunspots and their cycles
- Magnetic reversals and the spreading sea floor
- Magnetism in space and on planets.
- Your best approach is to read the material through--it is not too long, and may match your own interests. Then decide what of it can be applied in class, and how.
You may send comments, questions and corrections to my home address, earthmag("at" symbol)phy6.org. I will try to answer--but no promises, my schedule is already quite crowded!
- Among the subjects covered, one is somewhat more difficult from the rest, and is therefore best left out when teaching younger students. That is the notion of dynamos and of dynamo circuits. The teacher may skirt this area when the subject of the origin and reversal of the Earth's magnetic field comes up, by simply stating the bare facts, namely
- The slow variation of the Earth's magnetism, its high internal heat and the magnetism of sunspots suggest permanent magnetism is probably not involved in those phenomena.
- Theories exit, showing how flows in the fluid core of the Earth, caused by the heat generated there, can generate the electric currents responsible for the Earth's field.
- When volcanic lavas cool and harden, they take on (weakly) the local existing magnetization which exists at their location. The examination of the magnetization of such ancient lava flows suggests that in the past the north-south polarity of the Earth's field reversed directions, on the everage every half-million years or so.
- Final comment: translations to languages other than English are encouraged. Please contact me (earthmag("at" symbol)phy6.org) to work out the details. Your name will be credited with the translation, and as long as its use is free and non-commercial, you may place it on your own computer and/or on this one. We will try to help make the existence of translations known as widely as possible.
Dr. David P. Stern
31 Lakeside Drive
Greenbelt, MD 20770, USA