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Direction of magnetic field

  1. Apr 1, 2010 #1

    The explanation of this question is much more important to me than just the answer (I have an answer key for this practice test).

    Also, if someone could explain the different right hand rules pertaining to E&M and what situation(s) to use each in would be a HUGE help to me. I thought I had it down, but i keep confusing the hell out of myself!
  2. jcsd
  3. Apr 1, 2010 #2

    Doc Al

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    For this situation--the magnetic field surround a current-carrying wire--use the right-hand grip rule. Grip the wire so that your thumb points in the direction of the current--your fingers will be curling around the wire in the direction of the magnetic field.

    To solve the problem, you need to add up the field contributions from each current. (Remembering that they are vectors.)
  4. Apr 1, 2010 #3
    Doc has the basic explanation....or see here: http://en.wikipedia.org/wiki/Right-hand_rule

    You'll note that in your example problem some current fields add via the right hand rule and others cancel depending on current direction.....they will cancel when the currents oppose and the distance of point P from those currents are equal.
  5. Apr 1, 2010 #4


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    This is an obviously ill-posed problem. There is no point C. :p
  6. Apr 1, 2010 #5

    Doc Al

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    :tongue: Yeah, I had meant to point that out, but forgot. I assume it was a typo and that they meant point P. :cool:
  7. Apr 2, 2010 #6


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    Also, they did not place point P exactly between the two right-hand wires. The result will be a small downward component to B, in addition to what is probably the intended answer.
  8. Apr 3, 2010 #7
    Quite right. The resulting magnetic field will point in the viscinity of east by southeast, using cardinal direction (a bit south of due east.)
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