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Magnetic field of 2 infinite wires.

  1. Nov 6, 2011 #1
    1. The problem statement, all variables and given/known data
    Two thin, long wires situated in y = -a and y = a carrying two equal in magnitude and opposite running currents I.
    Find the field strength in therms of y.
    Find the average Field strength in a region -b to b, where 0 is between the 2 points.

    2. Relevant equations
    Amperes law.


    3. The attempt at a solution
    I find via. Amperes' law, that the field of the wire in -a (current running down) has the magnitude:
    [itex] B(y) = \dfrac{\mu_0 I}{2\pi r_1}[/itex]
    Where r1 is the distance from the wire, now i find that r1 = a-y.
    The field from the other is the same with the distance r2 instead of r1. r2 = a-y too so the field is zero and the average is of course also 0, and that is annoying. What have i done wrong.
     
    Last edited by a moderator: Nov 6, 2011
  2. jcsd
  3. Nov 6, 2011 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Better check if, for the downgoing wire, r1 = a - y.
     
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