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Total magnetic moment of simple system.

  1. Apr 23, 2016 #1
    1. The problem statement, all variables and given/known data
    If there's a current I flowing through the rectangular conductor and it's located in the magnetic field in such way that normal vector of the surface that this rectangle forms closes the angle of 60 degrees with magnetic induction vector find total magnetic moment of this system

    2. Relevant equations

    3. The attempt at a solution
    Formula for magnetic moment is m=SI where m is magnetic moment, S is the area of surface and I is the current. It is obvious that magnetic moment has the same direction as vector that is normal to the surface. This seems done to me now, but obviously it isn't since i am supposed to use the fact that i know direction of magnetic induction vector, but i just don't know how i am supposed to do that.
  2. jcsd
  3. Apr 23, 2016 #2

    Charles Link

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    The problem seems rather incomplete and/or misworded. With a magnetic moment in a magnetic field, there is a torque ## \tau =m \times B ##. (Formula is a vector cross product.). The vector cross product is the reason the angle of 60 degrees would be important. It seems a more proper question to ask would be "what is the torque on the magnetic moment?" ...editing...perhaps in very loose wording, a torque can also be called a "moment" because they call it a "moment arm" etc., but the "torque" should really be called the "torque".
    Last edited: Apr 23, 2016
  4. Apr 24, 2016 #3
    That's exactly what i thought, it might be that they meant a torque on the magnetic moment, but i wasn't completely sure. Anyway, i needed approval that i can't determine m by using the fact that i know B, i mean, that there's no formula that is used to determine m by knowing B.
  5. Apr 24, 2016 #4

    Charles Link

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    I think in a mechanics class I have heard the rxF's on a lever arm referred to as moments, but in E&M the word "moment" should be reserved for the "magnetic moment". The word torque is the proper term in E&M for the rxF generated when a magnetic moment ## m=I*A ## is found in a magnetic field ## B ##. This torque ## \tau=m \times B ##. The torque that occurs on a current loop of area A and current I in a magnetic field B is a simple follow-on from the force F that occurs on a wire of length L and current I in a magnetic field B: ## F=IL \times B ##.
    Last edited: Apr 24, 2016
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