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Question about eddy currents

  1. Aug 29, 2009 #1
    Okay so i just want to make sure i got this right because its a kind of confusing topic for me. So eddy currents are caused because when there is a motion (with a conducting surface) through a magnetic field a current is induced? and because there is a current there is also a magnetic field due to that current which opposes the original magnetic field and causes it to slow down?! Also when people are generating electrical energy by rotating a square/circle loop through a magnetic field do eddy currents slow you down? also I realize by cutting slots and other means you can reduce eddy currents. Thanks for the answers, and i hope my question was clear
  2. jcsd
  3. Aug 29, 2009 #2
    You got it pretty much right. But the eddy currents are only induced in a conducting material if the magnetic field is changing with time, or if a conducting material is moving through a magnetic field that is non-uniform (fcn of x, y, z), or rotating in a constant magnetic field.
    Last edited: Aug 29, 2009
  4. Aug 29, 2009 #3
    Why does the magnetic field have to be non-uniform?
  5. Aug 29, 2009 #4


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    Because something has to change over time; if the conductor moves through a uniform magnetic field, it's functionally static.
  6. Aug 29, 2009 #5
    Ahh makes sense now its becuase there has to be a flux right?, but there is no such thing as a uniform magnetic field right? except inside solenoids, but even then its not exactly uniform right?
  7. Aug 29, 2009 #6
    The basis for eddy currents is the integral form of Faraday's Law

    E dl = -(d/dt) ∫B·dA

    where ∫dl is around the perimeter of surface A.

    and J = σ E So
    " Ahh makes sense now its becuase there has to be a changing flux right?" Note the d/dt in Faraday's law.
  8. Aug 29, 2009 #7
    Thank you for the correction, and yes that is what I mean. Thanks for all the help guys, and the fast responses!
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