Quote:
MrkiMedo kaže:
Pogledajmo energetsku bilansu: neki mogu reci da se magnet
ne giba pa ne vrsi nikakav rad. Medjutim kroz magnet, buduci
da postoji magnetsko polje, teku struje - onda mora postojat
i rad. Dakle, mene zanima odakle dolazi ta energija?
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Magnetic fields don't arise only from classical moving charges. In fact the strongest and most interesting magnetic effects come from the spin of the electron. This is a quantum-mechanical effect with no correspondence in classical electromagnetism. The electron has a magnetic moment and angular momentum whose magnitudes do not dissipate.
Ferromagnetic materials such as Fe, Co, Ni, Sm, etc retain their magnetism indefinitely, just as they maintain electric charge, atomic mass, etc.
Since the interior of the Earth is largely Fe and Ni, magnetic fields at the surface of the Earth could be due to this intrinsic ferromagnetism (despite the high temperatures inside the Earth).