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Homework Help: Dielectric coax

  1. Oct 9, 2014 #1
    1. The problem statement, all variables and given/known data
    Show that (Grad dot E) =0 in the dielectric of a coaxial line.
    (Hint: apply the divergence theorem to a portion of the dielectric.)

    2. Relevant equations
    Divergence theorem

    3. The attempt at a solution

    I think I need to show that grad dot E = p/epsilon = 0

    I don't know - i'm stuck
  2. jcsd
  3. Oct 10, 2014 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    ... Well that would be false wouldn't it?
    Grad only applies to scalar fields. I think you mean "div" rather than grad.

    Do you know the equation for the electric field of a coax line?
    Do you know how to find the divergence of a vector field?
  4. Oct 10, 2014 #3
    Apply the divergence theorem --- do EXACTLY what the hint tells you. Simply apply the divergence thm and take Ea to be E from inner surface and Eb to be the E from the outer surface.

    Or, since we're probably in the same class read up on the divergence thm and dielectrics from the book.
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