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Homework Help: Force between two parallel wires

  1. Dec 5, 2007 #1
    1. The problem statement, all variables and given/known data

    Along horizontal wire carries a current at 48 A. A second wire,made of 2.5 mm diameter copper wire and parallel to the first,is kept in suspension magnetically 15 cm below.Determine the magnitude and direction of the current in the lower wire.Is the lower wire in stable equilibrium?

    2. Relevant equations
    F/l= u.I1I2/2(3.14)d

    u. -permeability of free space
    3. The attempt at a solution

    The second wire is not falling down so the current in both wires must be the same direction.I dont't have any idea how to get the force ,because there is no lenght and mass.
  2. jcsd
  3. Dec 5, 2007 #2


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    Homework Helper

    Since the second wire is hovering steadily, the magnetic force from the wire above it must be countering the second wire's weight. You don't need to know the length because your equation gives the magnetic force per length. So just consider, say, the forces on one meter of wire.

    What does one meter of this wire weigh? You are given a diameter for it and are told it is made of copper, so you can look up its density. This will allow you to find the mass and weight...
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