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Homework Help: Possible Helmholtz equation?

  1. May 31, 2007 #1
    Possible Helmholtz equation???

    1. The problem statement, all variables and given/known data

    Heres my problem: In recent studies of migrating birds using the Earth's magnetic field for navigation, birds have been fitted with coils as "caps" and "collars".

    a. If the identical coils have radii of 1.2cm and are 2.2cm apart, with 50 turns of wire apiece, what current should they both carry to produce a magnetic field of 4.5e-5 T halfway between them?

    I have no idea how to start/do this problem and don't know what equations I should use.

    2. Relevant equations

    B = uo(I)(L)

    3. The attempt at a solution

    I found B to be 56.4A, however, the correct answer is supposidly 21.5mA. How is this possible/what did I do wrong?
  2. jcsd
  3. May 31, 2007 #2

    Meir Achuz

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    Science Advisor
    Homework Helper
    Gold Member

    You have to use the formula for B on the axis of a loop.
    It is easy to derive using Biot-Savart.
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