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Homework Help: Flux Through a surface

  1. Feb 15, 2008 #1
    1. The problem statement, all variables and given/known data
    A volume in cylindrical coords is defined as [1,2]x[pi/6,pi/3]x[1,2]
    Calculate the flux of the vector field A(rowe,phi,z) = 4z (rowehat)

    Well I used the divergence theorem
    Volume integral( div(A) dot A dV) = pi
    I got pi as an answer, but apparently that is not correct.

    Does anyone know why the divergence theorem in this case doesn't work? I tried converting to Cartesian coords, the surface integrals are really nasty so I haven't evaluated them.

    My guess is that the flux is 0, however, how does one tell when the flux through a surface is 0 as opposed to a value? How do I know if the volume encloses a 'charge' in the case of gauss's law if I am just given a vector function?

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
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