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Em waves are self sustaining

  1. Jun 20, 2003 #1


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    in all the articles i have read it is said that em waves are self sustaining, if this is corect then they are perpetual motion, i thought that was not allowed???????
    Last edited by a moderator: Feb 5, 2013
  2. jcsd
  3. Jun 20, 2003 #2


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    Photons do not have mass. That means that they move
    through space but not through time - that means they
    always have the speed(of light) c according to relativity.

    Live long and prosper.
  4. Jun 20, 2003 #3


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    Re: em

    I believe that perpetual motion is allowed in the sense that it does not violate any physical laws. What is not allowed is a "Perpetual Motion Machine" that runs forever and also does work.

    You can have a process continue indefinitely without an external source of energy as long as you do not harness it or extract work from it. There must be no loss either--as for example due to friction or air resistance: which can be thought of as doing undesired work like heating something by rubbing or stirring up the air. To continue, the process must do no work.

    Light or EM waves can travel indefinitely in a vacuum, but if one sticks solar cells in their path to extract electricity then their motion stops being perpetual

    I suppose in an ideal superconducting ring you could start current flowing around the ring and then put the ring in an perfectly insulated box and the current would keep on circulating around the ring forever. Or until someone tried to get some work out of it.
  5. Jun 20, 2003 #4


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    how daft of me, thanks...
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