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Homework Help: Spring in a magnetic field

  1. Feb 16, 2014 #1
    1. The problem statement, all variables and given/known data

    A mass is attached to a spring through which circulates an electric current. Will the mass move?

    2. Relevant equations

    F = I l [itex]\times[/itex] B ?

    3. The attempt at a solution

    A spring is geometrically equivalent to a solenoid. Therefore, the current would generate a magnetic field which goes through the spring. What I'm not sure of is whether this magnetic field exerts a force on the solenoid or not.

    Thank you.
  2. jcsd
  3. Feb 16, 2014 #2


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    Consider what F = I l × B of a small section of the spring does on the current in the next loop of the coil. What is the direction of the resulting force ? (Ideal) springs are supposed to extend/contract in repsonse to forces in which direction ?

    Problem formulation is somewhat vague: was the current there when we opened our eyes, or was it switched on at that moment ?
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