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Strength of magnetic field from a current filled wire at a point

  1. Nov 12, 2008 #1
    [​IMG]
    that is the diagram that accompanies the question. The 3 parts of the question ask what is the magnetic field strength at points 1, 2 and 3.

    I know that B=B_1+B_2+.... for each point. In order to find the strength of the field at a point you must take into consideration all forces. I also know that u_0/4pi*(I s cross r/r^2) gives the strength of the magnetic field at a point, as does (u_0*I)/(2*pi*d)

    I have attempted the problem several times, and keep using the second equation from above for the points on the outsides of the 2 wires (points 1 and 3). However, I keep getting the answer incorrect. I haven't started point number 2, but I think once I figure out the principle behind points 1 and 3 it will come easier.
     
  2. jcsd
  3. Nov 12, 2008 #2
  4. Nov 12, 2008 #3

    gabbagabbahey

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    You need to consider the direction of the individual fields too, not just there magnitudes...if they point in the same direction at a given point, then the net field will be the sum of the two individual fields [itex]B_1+B_2[/itex], but if they are in opposite directions, you will end up with the difference of the two fields [itex]|B_1-B_2|[/itex]....use the right hand rule to determine the direction of the individual fields at each of the points in question.
     
  5. Nov 12, 2008 #4
    using the right hand rule, should B for the top wire should point out of the page and the bottom one into the page? my right hand rule is a little rusty.

    also, am i using the right equations?
     
  6. Nov 12, 2008 #5

    gabbagabbahey

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    Yes, the field at point 1 due to just the top wire is out of the page....how about the field at point 1 due to just the bottom wire?
     
  7. Nov 12, 2008 #6
    it should point into the page
     
  8. Nov 12, 2008 #7

    gabbagabbahey

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    Good, so the fields oppose each other at that point....so what is the net field then?
     
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