Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Do Magnets attract electrons?

  1. Feb 4, 2012 #1
    I know that magnetic fields can effect electrons in certain ways, but I specifically want to know if a bar magnet just sitting on a desk will attract "free electrons" much like a magnet will attract a paperclip. The reason for this question is my brother is working on a new type of battery that uses the magnetic field of a permanent magnet to generate electrical power (without spinning the magnet like in a generator). My brother is operating on the assumption that free electrons in a coil of wire will head towards a magnet when close enough, and he thinks he can use this to somehow generate electricity. I don't think it'll work but I'm a computer technician not a physicist.

    Edit: Also I apologize if I posted this in the wrong forums, I figured electrical engineering would be a good place to start since this is in relation to a new type of battery.
     
  2. jcsd
  3. Feb 4, 2012 #2

    DaveC426913

    User Avatar
    Gold Member

    It won't work, but not for the reason you think. Magnets are not a source of energy.

    He is as likely to do work with a magnet as he is to do work with gravity by dropping a heavy ball attached by a string to his motor. Yes he can extract some potential energy from gravity once, but he'd have to raise the ball again. He's not extracting energy from gravity he's extracting it from his own muscles, lifting the ball back up.

    Likewise, the way to get electricity from a magnet is to keep the wire moving in close proximity to it. But to keep the wire moving takes work.
     
  4. Feb 4, 2012 #3
    His goal is to create a "battery that never goes dead" His idea is to take a coil of wire with a diode (which will only conduct electricity in one direction, please correct me if I'm wrong) and use the magnet (not moving) to attract the electrons past the diode, in his mind after the electrons in the coil get past the diode they won't go back through the diode and as more electrons are attracted past the diode by the non moving magnet the electrons will effectively stack until they "spill" back over to the other side of the coil (and presumable after moving thrugh what ever he wants to power) where they will be attracted by the magnet again and the process starts over. Again I don't think this'll work be he won't take no from me.
     
  5. Feb 4, 2012 #4

    DaveC426913

    User Avatar
    Gold Member

    Let's grant that he gets the magnet to attract the electrons. This idea fails where every perpetual device fails.

    At some point, and quickly, the cumulative repulsion from all those electrons will prevent more electrons from passing through the diode. The system will grind to a stop in a fraction of a second.

    As with most of these perpetual devices, they might get a little work out of it while one cycle completes, but it is not sustainable over any length of time.




    It is important to note that discussions of perpetual device like this are forbidden of PF. I'm giving you some answers, but don't expect this thread to remain open.
     
    Last edited: Feb 4, 2012
  6. Feb 4, 2012 #5
    Thanks I figured something like that would happen, but back to my original question, does a magnet attract or simple effect electrons (by effect I mean like that elementary school experiment where you put the magnet under a piece of paper, sprinkle iron filings on top of the paper and the filings will line up to the magnet's field instead of just bunching up on the magnet). Sorry about being insistant on this one point but if I don't give my brother the exact answer he want's he'll just have 20 more questions or he'll just say he needs a bigger magnet.

    Sorry, this is my final post on the subject.
     
  7. Feb 4, 2012 #6

    DaveC426913

    User Avatar
    Gold Member

    Well, magnets do attract electrons, as anyone who owned a 20th century "tube" TV has witnessed.
     
  8. Feb 5, 2012 #7
    They don't, actually...they deflect them, the electrons experiencing a force perpendicular to their motion and to the direction of the magnetic field they're moving through, which is only sometimes toward or away from the magnet. And if the electrons aren't moving and the field's not changing, there's no force.

    http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfor.html

    Magnets in a generator are kind of like the vanes of a propeller, which push the air only when moving. All generators do is transfer mechanical power to electrons in wires, using magnetic fields as an intermediary. Trying to get electricity from a stationary magnet and wires is much like trying to make a propeller work without moving.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook