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Magnetic force does no work. OR does it?

  1. Nov 4, 2011 #1
    Hello Forum,

    it is well known that the magnetic force |F_mag|= q v B sin(theta) does no work on a moving charge particles, i.e. it does not increase or decrease its kinetic energy. It only changes its trajectory.

    However, in the examples of a U shaped wire loop with a movable metal bar that is free to slide, if we move the bar with velocity v while the loop is inside a magnetic field B, an induced emf= vBL is generated. It is said that the induced current (charges in motion) is due to the magnetic force....that seems an inconsistency: the charges are now set into motion by F_mag....So F_mag does work on them...or doesn't?

    thanks,
    fisico30
     
  2. jcsd
  3. Nov 4, 2011 #2

    Matterwave

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    The metal bar will slow down, the magnetic field is simply transferring the kinetic energy of the moving bar into the kinetic energy of the charges.
     
  4. Nov 4, 2011 #3
    Hi Matterwave

    so your point is that the magnetic force is not actually doing the work...it is just transferring it? Is the magnetic field kind of acting as a proxy you mean?
     
  5. Nov 4, 2011 #4

    Matterwave

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    Sort of I guess. It's just transferring one kinetic energy into another.
     
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