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Some physics problems? (Posted on 2006-04-16) Difficulty: 5 of 5
This was a problem I troubled myself with when the Physics teacher taught electromagnetism.

Assuming that we can create a gigantic alternating current generator in space, rotating a gigantic circular magnet around a gigantic wire coil to induce an alternating current, will we not get infinite energy and defeat the law of conservation of energy?

As the whole set up is in space, there is no friction whatsoever between the components though the wire naturally has some resistance. The wire's induced magnetic field can oppose the rotation of the magnet, but this can be easily be counteracted by routing a bit of energy from an external circuit to the magnet. As the magnet is circular the gravitational attraction between the circular magnet and coils cancels out. The power from the wire coil will then be connected to a device which will transmit the energy to earth via an electromagnetic wave.

The only energy inputs are that to keep the ring rotating and the initial energy input to put the setup in space. The output in energy is theoretically infinite.

SOMETHING is wrong with this argument that I later discovered myself. The Physics teacher was unable to detect it and walked away quite puzzled. Can you guys find out why this would never work?

See The Solution Submitted by Jack Lim    
Rating: 3.5000 (2 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
re: E = mc^2 | Comment 4 of 13 |
(In reply to E = mc^2 by Dej Mar)

Nice comment Dej Mar, Jack Lim is indeed to optimistic when he speaks about a theoretically infinite energy output.
But I think your answer doesn't solve the  real main point of the puzzle: we need to find a reason why in this construction, the energy input must be greater or a least the same as the energy output.  If we don' t find where the energy loss is, then we have a perpetuum mobile, which is impossible according to thermodynamics.

As for the friction question: an easier set up, that clearly has no friction would be the following, the results are the same as for -Jack Lim's.  The new model would eventually collapse once the gravitational forces let the rods touch each other.  Jack's circular set up does not have that.

Make a rod, one meter long, magnetise it, make it spin around its center.  Take a second rod, put that at 55 cm from the center of rod1, perpendicular to the plain rod 1 is turning in.  Everytime one of the poles passes, a current is induced in rod2.

  Posted by Hugo on 2006-04-17 05:43:26
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