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Homework Help: Three Infinite Straight Wires

  1. Feb 22, 2012 #1
    1. The problem statement, all variables and given/known data
    Three infinite straight wires are fixed in place and aligned parallel to the z-axis as shown. The wire at (x,y) = (-23.5 cm, 0) carries current I1 = 3.3 A in the negative z-direction. The wire at (x,y) = (23.5 cm, 0) carries current I2 = 1.2 A in the positive z-direction. The wire at (x,y) = (0, 40.7 cm) carries current I3 = 7.9 A in the positive z-direction.

    http://www.smartphysics.com/images/content/EM/14/h14_threewires.png [Broken]

    What is Fx(1), the x-component of the force exerted on a one meter length of the wire carrying current I1?

    2. Relevant equations
    Biot-Savart's Law: B=[itex]\frac{μ_{o}I}{2∏r}[/itex]
    Magnetic Force: F=ILxB

    3. The attempt at a solution
    I've tried using B-S to find each magnetic field individually, then find their forces individually, then combined together to get the total force. Using the arctan, I can get the angle of the force from the x-axis, which allows me to get the force in the x direction. I've also tried combining the fields together first and finding the angle then. I then use the force from the field. In both situations I'm getting a force of 7.138e-5N in the negative x direction, but apparently I'm wrong.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Feb 22, 2012 #2
    I figured out my problem. I was actually doing it right, but I'm using a different calculator, so I was inputing numbers wrong.
  4. Oct 12, 2012 #3
    I currently am on this problem with my homework. I thought this was correct. Thank you for the reassurance.
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