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Flux from a given charge distribution

  1. Feb 12, 2010 #1
    1. The problem statement, all variables and given/known data
    Three concentric spherical shells ,r=1m ,r=2m and r=3m, respectively, have charge
    distributions 2, −4, and 5 μC/m2.

    Calculate the flux through r=1.5m and r=2.5m



    2. Relevant equations

    Since we are talking about Gaussian surfaces I assume that the flux at 1.5m is just the flux contained in the 1m shell.

    I'm particularly having trouble figuring out what to do with the data. Given that the charge distribution is given in uC/m^2, I assume we need to multiply this by the surface area of each sphere to find the total enclosed charge (Qenc).

    Then I have that flux = Qenc0. But these answers seem way too high.


    3. The attempt at a solution

    SA1=4(pi)r2=4(pi)m2
    Qenc1=4(pi)m2*2uC/m2=8(pi)uC
    flux=8(pi)uC/ε0=2.84x106C
    where ε0=(10-9/(36*pi))
     
  2. jcsd
  3. Feb 12, 2010 #2

    rl.bhat

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    Your answer is correct.
     
  4. Feb 12, 2010 #3
    Thanks for the quick response. The whole mega-Coulomb just had me worried.
     
  5. Feb 12, 2010 #4

    rl.bhat

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    It is not mega -Coulomb. Flux is not measured in C, but in Weber.
     
  6. Feb 12, 2010 #5
    I've got it straightened out now. I was assuming eps0 was unitless. But even given that enlightenment, are these really mega-Webers that seems even more out of scale?
     
  7. Feb 12, 2010 #6

    rl.bhat

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    No. It is not out of scale.
     
  8. Feb 12, 2010 #7
    Thanks again. I have been working on the homework for this class for at least 30 hours on and off and it's only 7 problems. The professor's method of instruction and my method of learning just don't blend well and that's not his fault, I just need to learn a new way to learn.
     
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