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Homework Help: Magnetic Field with three parallel wires

  1. Dec 1, 2012 #1
    1. The problem statement, all variables and given/known data
    Three long, straight wires are carrying currents that have
    the same magnitude. In C the current is opposite to that
    in A and B. The wires are equally spaced. Each wire experiences a net force due to the other two wires. Which
    wire experiences a net force that has the greatest magnitude?

    A =====>====

    2. Relevant equations
    FAB = μ°I1 I2 / 2∏d

    3. The attempt at a solution
    It says that the answer is B because 2I squared / d is the net force on B. But the way I am doing it is -I^2/d + I^2/d = 0, hence the net forces cancel out and the force on B is zero. I don't understand how it is 2I^2/d. Please help.
  2. jcsd
  3. Dec 1, 2012 #2
    Hi rikinmathur! Welcome to pf! :smile:

    What are the direction of forces on wire B due to the other two wires?
  4. Dec 1, 2012 #3
    Hey rikinmathur, just think in terms of charges, maybe this is easier for you: A and B are positively charged (in a magnetic sense) and C is negative. So, which wire-pairs will experience an attractive and which a repulsive force?
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