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Magnetic field between two parallel wires

  1. Dec 18, 2009 #1
    1. The problem statement, all variables and given/known data

    Two parralel wires are 8 cm apart. The magnetic field halfway between them is 300 uT. What equal currents must be in the wires? Consider parralel and antiparralel currents

    2. Relevant equations
    I use Ia=Ib

    B = (u*i) / (2*Pi*distance) where distance = 0.04 m (0.08m divided by two since it is halfway)

    then I solve for I, I get 60 Amperes, the answers is 30 amperes

    What to do?
  2. jcsd
  3. Dec 18, 2009 #2
    Maybe you are not taking into account that the magnetic field is due to the current of _two_ wires
  4. Dec 20, 2009 #3
    Note that the forces on these two wires will attract eachother, combining together and forming double the magnetic field because the fields are in the same direction :)
  5. Dec 20, 2009 #4
    I think that it is correct for anti-parallel case. 30 A for each wire.
  6. Jan 11, 2010 #5
    you have to consider currents for both wires. so in this case current will b 2i.
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