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Eddy Currents

  1. Oct 12, 2014 #1
    1. The problem statement, all variables and given/known data
    A magnet of mass 0.10 kg is dropped from rest and falls vertically through a 35.0 cm copper tube. Eddy currents are induced, causing the copper to warm up. The speed of the magnet as it emerges from the tube is 1.50 m/s. How much heat energy is dissipated to the environment?

    2. Relevant equations
    E = mgh

    3. The attempt at a solution
    h = 35 cm --> .35 m

    E = (.10 kg) * (9.81) * (.35 m) = .3433 J

    Is the equation incorrect?
     
  2. jcsd
  3. Oct 12, 2014 #2

    ehild

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    It is the initial energy if you take the potential energy zero at the bottom of the tube. But what is the loss of energy?

    ehild
     
  4. Oct 12, 2014 #3

    NascentOxygen

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    What happens to the P.E. that you have just calculated the magnet loses?
     
  5. Jan 23, 2015 #4
    An illustrative experiment on this issue
     
  6. Jan 23, 2015 #5

    rude man

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    Good! We note that a larger-diameter tube slows the magnet down more than a smaller-diameter one, following emf = -dΦ/dt. Also that Cu slowed the magnet down more than did Al or brass, following i = emf/R. Vielen Dank!
     
  7. Jan 23, 2015 #6

    rude man

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    That's the kinetic energy (k.e.) that would have developed in the absence of the copper tube. What was the k.e. with the tube?
     
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