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Magnetic field and direction question.

  1. May 21, 2009 #1
    1. The problem statement, all variables and given/known data

    Calculate the magnitude and direction of the magnetic field 25cm to the east of a straight vertical wire with a current of 12A downward through the air.

    2. Relevant equations

    B = u(I / 2*pi*r)

    3. The attempt at a solution

    Finding the magnitude is simple, but finding the direction is giving me difficulty.

    The magnitude is 9.6E-6 T, and the direction is South. How is the direction South?
     
  2. jcsd
  3. May 21, 2009 #2

    berkeman

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    Staff: Mentor

    You use the right hand rule to determine the direction. If you grab hold of the wire (figuratively speaking) with your right hand, with your thumb pointing in the direction of the current flow, then your fingers curl around the wire in the same direction that the B field circles the wire.

    So grab the wire with your right hand with your thumb pointing down. Seen from above, do your fingers curl in the clockwise or counter-clockwise direction?
     
  4. May 21, 2009 #3

    berkeman

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    Staff: Mentor

  5. May 21, 2009 #4
    Clockwise, since the current faces downwards.

    So the direction for that point (east of the wire) is South because that is the direction the field faces when it connects with the point?
     
  6. May 21, 2009 #5

    berkeman

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    Staff: Mentor

    Correctomundo.
     
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