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Homework Help: Force per unit length acting on four parallel wires

  1. Jan 18, 2017 #1
    1. The problem statement, all variables and given/known data
    An arrangement of four wires, in cross section, with θ=30° and u=5cm. Wire 2 and wire 4 carry the same magnitude of current (I2=I4=10mA) directed out of the page. Wire 3 carries current I3=25mA directed into the page.

    If the resultant force per unit length on wire 1 is zero due to the other three wires, determine s, the distance between the origin and wire 3. Write your final answer in centimeters.
    2. Relevant equations
    F/L = (μoIaIb)/2πd

    3. The attempt at a solution

    I try to equate F2/L + F3/L + F4/L =0
    but now whats makes me confusing is I don't have the value of I1, so how should I continue it?
  2. jcsd
  3. Jan 18, 2017 #2


    User Avatar

    Staff: Mentor

    Look at the magnetic fields rather than the forces. The force on any current in wire 1 is due to the external magnetic field at its location.
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