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Homework Help: Flux out of a Cylindrical Cable

  1. Sep 14, 2011 #1
    1. The problem statement, all variables and given/known data

    A coaxial transmission line has an inner conducting cylinder of radius a and an outer conducting cylinder of radius c. Charge ql per unit length is uniformly distributed over the inner conductor and -ql over the outer. If dielectric [itex]\epsilon_{1}[/itex] extends from r=a to r=b and dielectric [itex]\epsilon_{2}[/itex] from r=b r=c, find the electric field for r<a, for a<r<b, for b<r<c and for r>c. Take the conducting cylinders as infinitesimally thin.

    2. Relevant equations



    3. The attempt at a solution

    For r<a there is no charge enclosed thus the flux is 0 so E is also 0

    Here is the solution they give for a<r<b. (see figure attached)

    I am confused as to how he determines the components of the vector [itex]d\vec{S}[/itex]. Is there a picture that will explain this?

    Thanks again!
     

    Attached Files:

  2. jcsd
  3. Sep 14, 2011 #2
  4. Sep 14, 2011 #3
    The wiki gives me the line, surface and volume elements but I don't want to have to memorize them.

    Isn't there a more intuitive way of understanding this as opposed to memorizing it?
     
  5. Sep 15, 2011 #4
    you are not suppose to memorize them, they should be given in the exams.

    you are suppose to understand how to get them

    take a look at these for more info

    http://www.math.ubc.ca/~feldman/m227/coordsys.pdf

    http://www.math.montana.edu/frankw/ccp/multiworld/multipleIVP/cylindrical/learn.htm [Broken]
     
    Last edited by a moderator: May 5, 2017
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