Magnetism

The Kids have been learning a bit about Magnetism.

There are a few categories of interesting examples

• the Planet Earth

  • approximate magnetic Di Pole

  • explained by Dynamo Theory, based on sloshing around of liquid iron in planet's outer core, but sounds suspiciously like a Perpetual Motion machine

  • more than 10deg off from geographic poles, and not exactly opposite each other

  • the Magnetic Pole-s are moving, some say accelerating

  • the poles occasionally reverse (north/south). Some have theorized that the recent acceleration in movement of the poles is a warning sign that a reversal will happen "soon". The effects of such a reversal are debated. Even if it doesn't trigger some crazy Climate Change, it could be mess with communication and computer systems (though probably less immediately/locally significantly than an EMP bomb, though obviously its effects would be global and longer-lasting).

• Permanent Magnet-s

  • The spin of an electron, combined with its orbital angular momentum, results in a magnetic dipole moment and creates a magnetic field. (The classical analogue of quantum-mechanical spin is a spinning ball of charge, but the quantum version has distinct differences, such as the fact that it has discrete up/down states that are not described by a vector; similarly for "orbital" motion, whose classical analogue is a current loop.) In many materials (specifically, those with a filled electron shell), however, the total dipole moment of all the electrons is zero (e.g., the spins are in up/down pairs). Only atoms with partially filled shells (e.g., unpaired spins) can experience a net magnetic moment in the absence of an external field. A ferromagnetic material has many such electrons, and if they are aligned they create a measurable macroscopic field. I hope you understood that.

  • Thus, an ordinary piece of iron generally has little or no net magnetic moment. However, if it is placed in a strong enough external magnetic field, the domains will re-orient in parallel with that field, and will remain re-oriented when the field is turned off, thus creating a "permanent" magnet. This magnetization as a function of the external field is described by a hysteresis curve. Although this state of aligned domains is not a minimal-energy configuration, it is extremely stable and has been observed to persist for millions of years in seafloor Magnet Ite aligned by the Earth's magnetic field (whose poles can thereby be seen to flip at long intervals).

• Electro Magnet-s

  • loop a wire over and over, run a current through it

Stimulating Learning Projects? well, you can play with iron filings, and make an Electro Magnet, but since nobody really can understand how they work, it seems more like a magic trick to me...

Jesus, why do they try Educating Kids about this stuff?