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Loudspeaker force on wire

  1. May 13, 2010 #1
    1. The problem statement, all variables and given/known data
    The magnetic field in a loudspeaker is 0.2 T. The wire consists of 270 turns wound on a 3.13 cm diameter cylindrical form. The resis- tance of the wire is 7.9 Ω. Find the force exerted on the wire when 11.6 V is placed across the wire. Answer in units of N.

    B=.2
    N=270
    r=1.565

    2. Relevant equations
    I have no idea


    3. The attempt at a solution
    I have no idea

    Please help me. I realize I am supposed to have tried i, but I have spent about haf an hour looking through my textbook and a studybook for similiar problems and haven;t found them, googled it, looked through this site and wikipedia, and I have no idea.
     
  2. jcsd
  3. May 13, 2010 #2

    collinsmark

    User Avatar
    Homework Helper
    Gold Member

    I'm guessing you're supposed to ignore the coil's self-inductance. So just find the steady state current of the coil using Ohm's law (the problem statement gives you the resistance and the voltage). You'll need to use this later.

    The look up "Laplace Force" or Google Force on a current carrying wire.

    You'll find an equation that is a function of the length of the wire. Since the problem statement gives you the diameter of the coil, and the number of turns, it shouldn't be too hard to use those to calculate the length.

    I'm guessing that you can assume that the magnetic field is always perpendicular to all of the wire in the coil. If you need a diagram to see what I'm talking about, check out this link:
    http://hyperphysics.phy-astr.gsu.edu/hbase/audio/spk.html#c1
     
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