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Find the magnetic moment

  1. May 28, 2015 #1
    1. The problem statement, all variables and given/known data
    Here we have two electrons rotating around z axis with angular speed w in a circle of radius R. They are on the same straight line (have difference in phase π). Find the magnetic moment.

    2. Relevant equations
    Magn. moment m=(1/2c)*∫dV [ r j ]
    3. The attempt at a solution
    Current J=dq/dt=qw/π;
    m=(qw/2cπ)*∫dr∫dφ r*r*δ(r-R)=qwR2/c
    Am I right?
     
  2. jcsd
  3. May 29, 2015 #2

    Simon Bridge

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    Is there a way you can verify this?
    i.e. have you compared this answer with the magnetic moment for just one electron, same circle and speed?
     
  4. May 29, 2015 #3
    Oh yes, I looked up a similar problem with 1 electron. There J=q/T; therefore m=0.5qwR2
    What about 1/c? Is it referred to the fact that I used CGS system of units?
     
  5. May 29, 2015 #4

    Simon Bridge

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    You should certainly compare like to like.
    Where does the c come from in the derivation?

    You can also check:
    http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magmom.html
    ... and derive the equation for a charge q going in a circle radius R.
    Note: the current I is the amount of charge passing a point on the circuit every second.
     
  6. May 30, 2015 #5
    Yes, I checked your link above. From their formula m=I*S it follow for 2 electrons m=qwR2 - no 1/c. This result corresponds to the result of 1 electron.
    But initially I tried to apply the general formula for m=(1/2c)*∫dV [r*j]; this formula was used in class where all tasks were done using CGS units.
    So, I would stick to my opinion that 1/2c comes from CGS...
     
  7. Jun 6, 2015 #6

    rude man

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    In SE units the c in the denominator would not be there. You on cgs or ???

    Nice fancy equation but you could have just said m = IA, I = current, A = area.
     
  8. Jun 6, 2015 #7
    Yes, I do use CGS here.
     
  9. Jun 6, 2015 #8

    rude man

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    As real physicists do! (I'm not one of them, I'm afraid) :frown:
    (I meant SI of course, not SE).
    rm
     
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