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Where does the energy come from?

  1. Feb 7, 2008 #1
    if you have a permanent magnet slotted into a laminated yoke like a transformer has. But this yoke has a telescopic piece which is made in the from of a bunch of wires running in line with the magnetic field . if this piece is pulled shut and open to increase and decrease the magnetic path resistance and there is a coil on the yoke and the increasing and decreasing magnetic flux creates electricity where does the energy for the electricity come from. I guess it comes from the phsyical force of moving the telespcopic piece but since this hopefully has little current in it is laminated to reduce eddy currents where does it get its' magnetic field from to resist movement. Can someone please explain this so I can stop thinking about it and get on with fixing my house.
  2. jcsd
  3. Feb 7, 2008 #2
    Have you seen the "perpetual motion" video of a similar machine? If so, that's a hoax. Enjoy fixing your house.
  4. Feb 7, 2008 #3
    er, the energy comes from work you spend to do so.

    There was an ancient, sorry prehistoric machine called ELEKTROPHORUS, sorry if i misspelt, that used to generate static electricity by moving a gatapercha or ebonite disk away and against attraction of a charged one.

    BUT THERE might well be flaws in this explanation -- i will probe.
  5. Feb 7, 2008 #4
    To tell the truth I did have in the back of my mind a fantasical machine of a perpetual motion kind. I have learnt about magnetic refrigeration so I was dimly hoping that the energy may come from heat energy been absorped somewhere in the apparatus. the energy to move the telescopic ( I'm going to call it a arm but it does not swing )you have the F=ma to accelerate it and a little resistance ? caused by eddy currents in the insulated sections which creates a magnetic field of their own to resist the movement. But perhaps these currents can be nearly eliminated or perhaps a magnetic sheilding material could be inserted and uninserted into the yoke, I don't know anything about magnetic sheilds but perhaps they don't conduct electricity very good so would not conduct eddy currents.
    Last edited: Feb 7, 2008
  6. Feb 9, 2008 #5
    I think I get it now the arm is always trying to shut because it acts like a solenoid so there is a overcoming force that must be applied to open it which is where all the energy comes from.
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