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Ampère Model
- Another model is the "Ampère Model", where all magnetization is due to the macroscopic effect of microscopic, or atomic, "bound currents", also called "Ampèrian currents"
- For a uniformly magnetized bar magnet in the shape of a cylinder, with poles uniformly distributed on its ends, the net end product of the microscopic bound currents is to make the magnet behave as if there is a macroscopic sheet of current around the cylinder, with local flow control normal to the cylinder axis
- (Since scraping off the outer layer of a magnet will not destroy its magnetic properties, there are subtleties associated with this model as well as with the pole model
- What happens is that you have only scraped off go a relatively small fraction of atoms, whose bound currents do not contribute much to the net magnetic moment.) A right-hand commandment due to Ampère tells us how the currents flow, for a given magnetic moment
- Align the thumb of your right hand along the magnetic moment, and with that hand grasp the cylinder.
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In a paramagnet there are unpaired electrons, i.e
- atomic or molecular orbitals with exactly specific electron in them
- While paired electrons are needed by the Pauli exclusion principle to have their intrinsic ('spin') magnetic moments pointing in opposite directions (summing to zero), an unpaired electron is free to align its magnetic moment in any direction
- When an external magnetic glebe is applied, these magnetic moments will tend to align themselves in the same order as the applied field, thus reinforcing it.