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Homework Help: Magnetic force between 3 straight wires

  1. Apr 5, 2004 #1
    Find I2 so that the magnetic force per unit length on each wire is zero. The three parallel wires are equally spaced. Current directions are shown with '<' or '>'.

    I1 = I3 = 1 A

    < I1 < I1 < I1
    > I2 > I2 > I2
    < I3 < I3 < I3

    I have the formula F = (mu0*I*I')/(2*pi*r) with mu0 = 4*pi*10^-7 but have no clue where to take this to figure out I2 with the 3 wires.

    Sorry if this is really easy but I'm not too quick with Physics. Thanks for any help.
  2. jcsd
  3. Apr 6, 2004 #2
    r in the formula is the distance between 2 wires. So let r = distance between wire 1 and wire 2. Then the distance between wire 1 and wire 3 is ______?

    Next, use that formula to find the force exerted on wire 1 by wire 2, and the force exerted on wire 1 by wire 3. If the NET force on wire 1 is 0, those two forces must be equal in magnitude & opposite in direction so set the two F's equal to each other & solve for I2.
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