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Reality of bound currents

  1. Dec 5, 2014 #1
    A magnetized object is always described as having bound volume and surface current. Are these bound currents real? I mean if I connect a galvanometer between two points on the surface of a magnetized iron sphere, will the galvanometer show a deflection?
    If it does then it is very strange because Iron is magnetized because of the spin of its electrons which are point particles. So they can't really create a "flow" of charge along the surface to create a surface current. How then can we explain the "reality" of surface current?
  2. jcsd
  3. Dec 5, 2014 #2


    Staff: Mentor

    Let's suppose that the current were real. How much deflection would you expect to see on the galvanometer?
  4. Dec 5, 2014 #3
    I think no deflection should be seen as there is no charge that is flowing along the surface. In Griffiths text on Electromagnetism, the author has explained the surface current as being caused due to tiny current carrying loops whose current "touches" the surface. The cumulative effect of all such loops would be a surface current (although it is not due to continuous flow of charge). But in real materials there are no such tiny loops inside but electrons instead of them which are point particles. So now we evidently cannot explain the surface current. So in this case, the surface current is not there apparently and is just an imaginary physical model to describe the magnetization. Am I right here?
  5. Dec 5, 2014 #4
    No deflection of no galvanometer. You're right.
  6. Dec 6, 2014 #5


    Staff: Mentor

    You are correct, no deflection should be seen. A galvanometer measures current through the galvanometer. The bound current is bound to the surface of the magnet, so it doesn't flow through the galvanometer.

    My point is, if you want to decide if something is "real" then you have to figure some experiment that would be different if it were real or not. The galvanometer is not such an experiment because regardless of whether it is real or not it doesn't flow through the galvanometer and therefore you don't expect anything different.

    I cannot think of any such experiment, so I don't think that the "is it real" question is scientifically meaningful.
  7. Dec 7, 2014 #6


    User Avatar
    Science Advisor

    Who sais that electric current is only flow if charge?
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