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Homework Help: Conducting wire

  1. Mar 3, 2007 #1
    1. The problem statement, all variables and given/known data
    A long, straight conducting wire of radius R has a nonuniform current density J=J0*r/R, where J0 is a constant. The wire carries total current I.
    Find an expression for J_0 in terms of I and R.
    Find an expression for the magnetic field strength inside the wire at radius r.

    2. Relevant equations
    B*ds = u0*I

    3. The attempt at a solution

    So from my book it looks like J0=I/A which is Jo=I/(pi*R^2) which says it is off by a multiplication factor not sure where Im going wrong here. As for the second portion I got B= uo*I*r/(2*pi*R^2) which is also wrong so any help on this would be much helpful.
  2. jcsd
  3. Mar 3, 2007 #2
    Since J is a function of r, it will be constant for a thin cylindrical shell centered on the wire. Adding up the current in all these shells will equal I.
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