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Homework Help: Magnetic field strength between two wires

  1. Feb 11, 2010 #1
    wire 1 has a current of 1A directed into the page, wire 2 is 20 cm to the right of wire 1 with a current of 1A, what direction does this current have to flow in order for the magnetic field strength at the mid point between them to be non zero ?

    from the right hand rule the mag field from wire 1 would be counterclockwise around the wire so the current on wire 2 would have to be the same direction - into the page with a counterclockwise field other wise the fields would cancel

    do i haev this correct & did i explain myself properly ? the next part of the Question depends on this answer
  2. jcsd
  3. Feb 11, 2010 #2
    The current into the page gives a clockwise field via the right hand rule, if I'm not mistaken. Draw a picture, I think you came up with the wrong conclusions.
  4. Feb 12, 2010 #3
    thanks for pointing that out, i have drawn a picture of the wire and i can see now that the current is clockwise, so i think that the current in the other wise also needs to be into the page otehrwise they will cancel,

    the next part of the question is -
    Consider a general point on the line joining the two wires and a distance d away from the mid-point O. By summing the magnetic field due to currents of magnitude i flowing in both the wires in the senses you found.

    show that, on the line joining the two wires, the magnetic field strength is given by
    B= μo iD/ PI (D^2 − d^2 )

    I know the equation is

    B = μo i / 2*pi*d

    and (D^2-d^2) can become (D+d)(D-d) but i dont know where to go from there
  5. Feb 12, 2010 #4
    Last edited by a moderator: Apr 24, 2017
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