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Homework Help: Current Balance experiment (Earth's magnetic field?)

  1. Apr 14, 2007 #1
    1. The problem statement, all variables and given/known data

    There are two current carrying wires carrying the same current but in opposite directions. One wire is rigidly fixed whereas the other is part of a frame that can rotate about a horizontal axis. When current begins to flow in the two wires, they repel each other. The upper wire begins to rotate but if a mass is hung from it, the net force on it can be balanced so that it remains in mechanical equilibrium. Equating the weight to the magnetic force on the wire can be used to estimate the permeability of free space ([itex]\mu_{0}[/itex]) by drawing a straight line between the mass required to equilibrate versus the square of the current.

    Now, the questions is: how does one eliminate the effect of the earth's magnetic field?

    2. Relevant equations

    3. The attempt at a solution

    Will flipping the table be sufficient? :smile:
  2. jcsd
  3. Apr 14, 2007 #2


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    Gold Member

    Do you mean - take two readings in two different alignments to the earth's M field ?

    That would work. A more usual way is to use a pair of Helmholtz coils to null the field near the apparatus.
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