If electricity can be generated by moving a coil through a magnetic field, why do we not launch large coils into orbit? As they circled Earth within the planet鈥檚 magnetic field, the energy could be sent down from the coils via microwave: even people in remote areas could receive it. I suspect that this system would cost much less than energy generation does at present. So tell me, what flaws in this scheme would prevent me from picking up my Nobel prize?
You can鈥檛 get electrical energy for free; some other form of energy must be drained. When a coil moves though a magnetic field, the electric current that this induces generates a force that acts to oppose the motion of the coil. So in a dynamo, for instance, an external form of mechanical energy is needed to keep the coil spinning. In a coil orbiting Earth, the induced force would slow the coil down, causing it to fall from orbit and plunge to Earth.
If you mounted a rocket on the coil to keep it in orbit, you would find that the amount of electrical energy generated would never exceed the amount of energy you spent keeping the coil in orbit, not to mention the exceedingly large amount of energy required to get it into orbit in the first place. So sorry, no Nobel prize.
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Simon Iveson, Mayfield, New South Wales, Australia
This idea would waste far more energy than you could ever generate from the coil. It is not without merit, however. NASA has experimented with conductive tethers in orbit. They have tried using them both to generate electricity from the motion of a satellite around the Earth and, by reversing the process, to change the orbit of a satellite around Earth by passing electricity through the tether (see New 杏吧原创, 17 February 1996, p 23 and 2 March 1996, p 13). They were not successful, and neither were more recent efforts 鈥� see http://space.newscientist.com/article/dn11836.html.
Jon Webb Pittsburgh, Pennsylvania, US