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Cylindrical charged surface

  1. May 26, 2015 #1
    1. The problem statement, all variables and given/known data
    An infinitely long cylindrical surface of circular cross-section is uniformly charged lengthwise with the surface density σ = A cosΦ where Φ is the polar angle of the cylindrical coordinate system whose z axis coincides with the axis of the the given surface. Find the magnitude and direction of the electric field strength vector on the z axis.

    Source: Irodov

    2. Relevant equations

    3. The attempt at a solution
    Since σ depends only on Φ, according to cylindrical coordinate system, σ is different on different planes that pass through z = 0. I just don't know where to begin, I looked up the answer and it didn't make sense to me very much.
    Please just tell me how to start!
  2. jcsd
  3. May 26, 2015 #2
    On axes x,y make the expretion of electric field components E_x, E_y for the field on the x=0, y=0 and take integrals to whole circle and z. May polar coordinates be more useful.
    Also may Gauss's law be useful.
  4. May 26, 2015 #3


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    Don't you mean through r=0?
    Consider a section through it at some value of z. What does the charge distribution look like? Does it vary with z?
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