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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: thermodynamics (& other musings) | Comment 12 of 13 |
(In reply to thermodynamics by matt)

matt's statements are correct, but entropy is not quite what he states.  Entropy is something like the amount of "dis-order" required to have an energy state greater than zero.  Chemical energy comes from electrical bonds that are made to release that cohesive force.  Thermal energy comes from the motions (kinetic energy) that particles have due to thier speed and mass.  Nuclear energy comes from the energy equivalence of the actual mass of elemetary particles themselves.  In any event involving energy transefer, entropy is increased - bonds are brken, temperature is lost, a small bit of mass is converted directly into energy.  This cannot be reversed without adding energy from "outside the system" that is being analyzed/discussed.  If one takes the entire universe as the "system", then we have no where for this energy to come from.

Although the maximum entropy state of the universe is an "equilibrium" at absolute zero, it is not the defintion of that term.  All kinds of equilibriums exist, at any energy level.  Equilibrrium merely implies that there are no forces (or work, or energy) coming from the "outside" to the "inside" of the system under study.

Also, about friction - being in space does not negate all friction.  Yes, since friction depends on normal forace between surfaces, then there is no normal force between say, two block of wood that are made to touch, vs. what you would get on earth if one were put on top of the other.  However, in a roatating machine, with, presumably, ball bearings, there are tight fits and contact/motion between the balls and the races, and friction would be non-zero.

Edited on September 29, 2006, 4:12 pm
  Posted by Kenny M on 2006-09-29 16:07:33

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