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Homework Help: Treee more long wires

  1. Mar 16, 2009 #1
    1. The problem statement, all variables and given/known data
    Three long parallel wires are 4.0 cm from one another. (Looking along them, they are at three corners of an equilateral triangle.) The current in each wire is 8.00 A, but its direction in wire M is opposite to that in wires N and P. By convention we can say that M is at the top of our equilateral triangle and N on the lower left hand corner.

    Determine the magnitude and direction of the magnetic field at the midpoint of the side of the triangle between wire M and wire N.

    2. Relevant equations
    B = [tex] \frac{\mu_0 I}{2 \pi r}[/tex]

    3. The attempt at a solution
    I was put these answers into mastering physics and I got the angle wrong. I have tried tan(P/2M) and tan(2M/P) where M and P are the magnetic fields from M and P respectively.

    Am I doing something wrong? Its given units are 'degrees below horizontal' and I have no idea what, exactly, is meant by the horizontal. Many thanks for any input!
  2. jcsd
  3. Mar 17, 2009 #2


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    Homework Helper

    Hi Queue

    I think you are determining the angle of a triangle formed by the perpindicular components (ie from M&N vs P components). These are perpindicular & parrallel to the triangle side MN respectively.

    This is the first step, however the question asks the angle form a horizontal line. What is the angle between MN side & the horizontal? (what are the angles of an equilateral triangle?)

    drawing a picture is usually always a good idea if you haven't already - cheers
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