Naked Science Forum
General Science => General Science => Topic started by: Mononoke on 01/04/2014 13:46:18
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I wasn't so sure where questions relating to magnetism belonged more specifically so I posted it here.
I have a few questions about magnetism that I'd love to have answered (and that I've already tried to find answers for online to no avail).
1. Is our earth’s magnetic field stronger nearer the core (as isn’t that where it emanates from)? However, I thought higher temperatures prevented strong magnetic forces from ‘occurring’ so what gives?
2. How much stronger could the earths magnetic field viably ever be and what effect would this have on the surface and in particular on living organisms?
3. If the magnetic field was stronger, and if certain ferromagnetic materials were in abundance within larger rock formations, could rocks conceivably levitate?
With Question 3, its my understanding that according to Earnshaw's theorem that's not possible and that additional means are necessary so could someone explain exactly what these other means (superconductors, diagmagnetic materials etc) exactly are in less technical terms and how they work (as I don't really understand this part).
Lastly, is all of this possible as a natural occurence without any human hand involved.
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1. The magnetic field is probably stronger at the pole of the core than at the poles of the surface, just due to proximity. Heat interferes with ferromagnetic magnetism by scrambling the electronic states of the material (if one heats a permanent magnet, which has more electrons in one spin state than the other, as the temperature increases, the electrons re-equilibrate, minimizing the field). However the mechanism responsible for the Earth's magnetic field is more like an electromagnet than a permanent magnet: it is due to circular motion of charges. This is not so dependent on temperature.
I think the point of confusion is that the core is made of iron. My understanding is that we would see essentially the same effect if it were copper or gold (or metallic hydrogen, as has been posited as the source of Jupiter's magnetic field...)
2. I'm not sure, but I think the current field strength is pretty close to the historic maximum. Certainly it has been a lot smaller (even going to net zero as the polarity inverts)
3. Ferromagnetic materials would not levitate in an applied magnetic field without some very special constraints. A simple re-orientation followed by attraction would be the expected outcome (like a compass needle)
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3. If the magnetic field was stronger, and if certain ferromagnetic materials were in abundance within larger rock formations, could rocks conceivably levitate?
A magnet suspended above another magnet will often spin around and then they the two magnets will stick together. However, magnetic bearings do exist with magnetic repulsion between them - you may have one in your house, if you have an old-style electricity meter with a spinning aluminium disk. But this requires magnets which retain their magnetic field despite external magnetic fields; most natural magnetic minerals are "soft", and will remagnetise in the presence of a strong external field.
The Meissner effect (http://en.wikipedia.org/wiki/Meissner_effect) uses a non-magnetic material which repels an external magnetic field, and will float above an external magnet. But this relies on superconductivity, which (as far as we know today) only exists at very low temperatures. So you might need to go to Pluto to see it working - the lower gravity would also help (or, on Earth, use liquid nitrogen to cool it down to superconducting temperatures).