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Homework Help: Finding Magnetic Field at Point P

  1. Oct 26, 2008 #1
    1. The problem statement, all variables and given/known data
    Two long thin parallel wires 13 cm apart carry 25A currents in the same direction. Determine the magnetic fild at point P 12 cm from one wire and 5 cm from the other.

    2. Relevant equations
    B=mu/2pi * I/r

    3. The attempt at a solution

    I have already solved this problem, and I have the answers. The problem is I wasn't too specific when doing it and now cant figure out for the life of me how I got the angle I used!:eek: when I use ratios like (.12/.13) instead of Cos theta it works out opposite, for the other current carrying wire. How do I know what is theta? I remember vaguely doing something like 90-theta then doing cos/sin of that to find the xy components. Helping me with this would mean a LOT to me guys. I checked the book for similar examples, none. Only ones where forces are all x or all y with no components.

    EDIT: I have the angles now, but I'm still unsure which to use for which current carrying wire. I have 67.4 and 22.6. Do I do 90 - the angle I get fr each current carrying wire since the B field is perpendicular?
    Last edited: Oct 26, 2008
  2. jcsd
  3. Oct 28, 2008 #2


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    Homework Helper

    Hi 0338jw,

    Are you referring to finding the components of each field? That would depend on the angle that the line to point P makes with the coordinate axes. Are the point and the two wires all in a line, or are they arranged somehow else? Can you upload a picture, or provide more description?
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