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Homework Help: Determining Electric Flux for cylindrical surfaces

  1. Sep 10, 2008 #1
    1. The problem statement, all variables and given/known data
    Cylin. surfaces [tex]\rho[/tex] = 1 , 2 , 3, cm have uniform surface charge density of 20, -8, 5 nC/m^2.

    What is the total electric flux that passes through the closed surface [tex]rho[/tex] = 4 cm and z(from 0 to 1 m)?

    And what is [tex]\vec{D}[/tex] at the point [tex]\rho[/tex]= 4 cm , [tex]\phi[/tex]= 0 , z = .5 cm

    2. Relevant equations
    [tex]\Phi[/tex]= E2piRL=[tex]\lambda[/tex]L/8.85x10-12
    E = [tex]\rho[/tex]/(2pi8.85x10^-12 [tex]\rho[/tex])

    3. The attempt at a solution

    So the closed surface from which to determine the flux is at [tex]\rho[/tex] = .04 m

    I frankly am unsure how to use the equations to get the total flux.

    [tex]\Phi[/tex]1 = 20(.01)/8.85x10^-12
    [tex]\Phi[/tex]2= -8(.02)/8.85x10^-12
    [tex]\Phi[/tex]3= 5(.03)/8.85x10^-12

    Is it as simple as adding them all up? Or does the center most cylindrical surface at 1 cm have an affect on 2 cm surface which then in turn affects the 3 cm? I have a feeling this is completely wrong so I attempted it a different way

    total flux = sum of the integrals?

    I obviously am struggling with this concept any help would be appreciated Thanks!
  2. jcsd
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