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Since the Earth has a magnetic field, can it, in theory, be run through a conductive metal coil to create electricity?

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up vote 11 down vote accepted

Not really. A magnetic field alone doesn't create electricity. A changing magnetic field does. The Earth's magnetic field does change a tiny bit but not enough to really generate much.

The other option is to move the inductor in the magnetic field. The Earth's magnetic field is quite homogeneous over short distances though so the coil would need to move fast and very far to generate much. This would use more energy than it creates (at least on the surface of the Earth).

Several years back there was an experiment (the Space Tether Experiment) to drag a conductor through the Earth's magnetic field with the Space Shuttle. I don't know how viable this is though because I think it saps orbital energy.

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"The Earth's magnetic field is quite homogeneous over short distances though so the coil would need to move fast and very far to generate much." You can just spin a coil. The issues are that: (1) the earth's field is weak, and it's easier to use the field of a stronger permanent magnet; and (2) as with any generator, it requires an input of energy to turn the crank. – Ben Crowell May 19 '13 at 3:45
@BenCrowell I think we're in agreement. I was not imagining the coil spinning. I was imagining it on a train or something like that. But my point was that you'd have to make it move really fast and really far to generate anything useful and the energy needed to move it would use far more than in generated. – Brandon Enright May 19 '13 at 3:46
If you put in energy into the coil, there seems to me no reason that you couldn't then get momentum out of it. I don't know how viable this would be in practice, but in theory it seems like you could use a coil to push against the Earth and slowly raise or maintain your orbit. – Alan Rominger May 19 '13 at 3:49
The efficiency would depend on the quality of the bearing. There is no fundamental reason that it has to be inefficient. The coil doesn't have to move far or fast. If it has some large number of loops, you can generate a large emf by spinning it slowly. – Ben Crowell May 19 '13 at 3:58
@AlanSE also as far as efficiency goes for keeping the orbit one should do the energy balance between small rockets/jets and spending it in rotating a gismo. – anna v May 19 '13 at 4:28

I've been thinking about this lately but I think that u missed something you all are saying that much energy will be needed to make the coil spin I've an objection on this it depends on the shape of the coil and its position also material used. I think if the coil was made to be wide and not long and just flought horizontal away enough from the earth surface at the equator and kept rotating horizontally u won't need much energy to keep it rotating and as far as u go farther than the magnetic source distance between magnetic flux lines will increase so variation in magnetic flux denisty will be achieved easier and using wide coil will increase contact points decrease average weight and decrease its electric resistance.

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Actually, it's possible to use the Earth's magnetic field to generate electricity. A satellite in the form of large diameter loop in orbit around the Earth will generate a current in that loop, and could be used to power something, but at the cost of a rapidly degrading orbit. On the other hand, solar panels creating a current in that same loop could boost the satellite into a higher orbit.

Transferring power out of an orbiting system of this type to somewhere else , and the technical issues involving superconductors are large.

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protected by Qmechanic Dec 23 '13 at 12:25

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