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Homework Help: Magnetic Field of Currents

  1. Sep 26, 2008 #1
    1. The problem statement, all variables and given/known data
    A long current-carrying wire, oriented North-South, lies on a table (it is connected to batteries which are not shown). A compass lies on top of the wire, with the compass needle about 3 mm above the wire. With the current running, the compass deflects 10 degrees to the West. At this location, the horizontal component of the Earth's magnetic field is about 2e-5 tesla.

    What is the magnitude of the magnetic field at location A, on the table top, a distance 2.9 cm to the East of the wire, due only to the current in the wire?

    2. Relevant equations
    Bnet = Bearth + Bwire

    3. The attempt at a solution
    I know Bearth = 2e-5, and taking into account that Bnet would be the deflection, I obtained 2.0308e-5 for Bnet, and hence, Bwire would equal to 3.08532e-7. I don't really know where to go from here.
    Thanks in advance.
  2. jcsd
  3. Sep 26, 2008 #2


    User Avatar
    Homework Helper
    Gold Member

    Well, you've calculated Bwire at r=3mm, so what does that make I? what does that make bwire at r=2.9cm?

    Edit- you might also want to show us your calculation of Bnet, because I don't think it is correct.
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