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Magnetic field in conductor

  1. Mar 17, 2009 #1
    I have two conductors in no magnetic material such as copper. One has diameter 20mm and other has diameter 50mm and both through by same current about 100A. Where do i have the maxi magnetic field on surface of conductor...I tinks on conductor with diameter 20mm..Is exactly ???
  2. jcsd
  3. Mar 17, 2009 #2


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    For the same current, the magnetic field at the surface is proportional to 1/R.
  4. Mar 18, 2009 #3
    Tanks cleam.. Excuse me for the stupid question but i had one discussion with my friend which sayed that the magnetic field at the surface was higher on conductor with diemater 50mm ...
  5. Mar 18, 2009 #4
    If the two conductors are isolated from one another, the higher field is at the surface of the 20 mm conductor. The B field outside an infinite straight conductor of radius R is

    B = 2 x 10-7 I/a tesla (a>R)

    where a is the distance from the center of the conductor. The field inside the wire is

    B = 2 x 10-7 r I/R2 tesla

    where r is a point inside a conductor of radius R (r<=R)

    So the field scales as r inside the conductor, and 1/a outside. If the current is an AC current, Eddy currents force the currents toward the surface of the conductor.
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