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Magnets and coils question

  1. Jun 25, 2010 #1
    I've already done an experiment to show that if I take two coils and connect the leads together I can physically move one magnet towards the first coil and it will draw a second magnet towards the second coil. Of course this depends on how you wire the coils together as it can also repel the second magnet if you reverse the leads.

    Assume I've wired them such that the second magnet will be attracted. The first magnet is inducing a current in the first coil building a magnet field causing a magnetic field to also be created in the second coil which is what attracts it.

    My question is; What happens if both magnets are being mechanically moved towards their respective coil? Is the induced current/field doubled or is the second one negated because the magnetic coil 'matches' the induced field?

    I probably didn't explain that very well but I'm wondering if you could use this to not only keep magnet 'in synch' (where you want them respective to each other) but also create more current if they happen to be in synch as they are moved?


  2. jcsd
  3. Jun 25, 2010 #2
    The voltages/fields/currents are canceled out.

    If you ignore resistance, pushing the first magnet into the set of coils while holding the second still (or just pretending the second magnet does not exist) will develop a current and a field. The coil's field will be opposite polarity to the magnet's, and the two fields will be under tension. Energy will be stored.

    If you push the first magnet while letting the second move, the motion of the second will also induce a field--a field opposite the original induced field. The original current is canceled out and the first coil loses its field too. It's not about matching fields or having them overlap. Actually, if the second magnet's polarity is flipped and it moves away from the coil, the same induction and canceling will happen. Anyway, no energy ends up stored anywhere. In fact, moving the first magnet will require no force or energy (ignoring the magnet's mass and inertia). The distance by which the second magnet moves will be the same as the distance by which you move the first.

    If you push the second magnet while pushing the first.... well, there's no sense in that. You'll only be causing both magnets to move more quickly.
    Last edited: Jun 25, 2010
  4. Jun 27, 2010 #3
    Hmm....not sure I follow. What I'm trying to do;

    I have four pistons with magnets in them oscillating back and forth, each 90 degrees out of phase of the previous. The pistons have different pressures on them at different times during the stroke. Can I use multiple coils around the pistons and the magnets in the pistons to keep the magnets/pistons more in synch with each other and at a more uniform speed? I know even if I could do this I'd have to have some circuitry to change the coil lead connections since the piston changes directions.


  5. Jun 27, 2010 #4
    "[URL [Broken] law[/URL] might help.
    Last edited by a moderator: May 4, 2017
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