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Difference in potential induced by a magnetostatic field? O_o

  1. Sep 7, 2009 #1

    Why is there a difference in electric potential from a point on the surface of a stationary magnet to a point on a conductor that is placed underneath a dielectric? I placed some stationary magnets on top of glass or a piece of paper and put some aluminum under it, and touch one end of a voltmeter to the magnet and the other end of the voltmeter to the aluminum, the most I got was like 0.5 volts. When I remove the paper the potential difference is zero. If I remove the magnet, the potential difference is zero. When I have the magnet there at rest on top of the paper, which is above the aluminum, the potential difference is nonzero. When I start moving the magnet and the paper away from each other, the potential difference starts dropping quickly.

    I thought that only a magnetic flux that is changing could induce a difference in potential. Anyone got an idea what's going on here?
  2. jcsd
  3. Sep 12, 2009 #2


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    Welcome to PF!

    Hi Vectronix! Welcome to PF! :smile:
    That's interesting … does anyone else know the answer? :smile:

    (btw, does the potential difference reverse if you turn the magnet over? and does it work with other metals?)
  4. Sep 12, 2009 #3
    Hi Vectronix-
    This is a very good question, as is the suggestion by tiny-tim-
    Are you talking about a dc potential, or a transient pulse (like discharging something). What is the input impedance of your voltmeter? If is something like 20 megohms. and the distributed capacitance is certainly less than a nanoFarad, then the transient would be less than RC = 0.02 seconds. You also told us that there is no dc circuit (loop), so there can be no current, or contact potential. So it is a puzzle.

    By the way, do you happen to have an analog voltmeter with a D'Arsonval movement? See
    Is it affected by stray magnetic fields?
    Bob S
  5. Sep 27, 2009 #4
    Hey, muchachos. :)

    I'm sorry, I have been busy for a while, and I wasn't able to get to this sooner. Yes, the potential difference reverses when I flip the magnet over. It is a DC potential, not a transient pulse. The voltage started off at a certain level then it decreased some and stabilized after a short while when I did this. Yes, it works with different metals. I tried aluminum and copper.

    I was thinking that maybe the dielectric that I use (paper, glass, etc.) and probably every other dielectric and its electric fields influence the magnetostatic field of the magnets I use thus becoming a time-varying field (changing magnitude and/or direction). But I am not sure why, if that is true. Any thoughts on this explanation? Anything to add to it? I will answer the other questions soon.
  6. Sep 28, 2009 #5
    Hi Vectronix-
    Did you know that analog meters with D'Arsonval movements have moving magnets inside? Keep your magnets far away from these meters.
    Bob S
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