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Maximum voltage on coaxial cable?

  1. Jun 12, 2015 #1
    1. The problem statement, all variables and given/known data
    How to determine maximum voltage that coaxial cable, whose height is L and is filled with dielectric in such way that E is the same in the dielectric and in the part of the cable that isn't filled with dielectric (only vacuum),can handle if i have maximum electric field that is E=3MV/m, and i have inner radius a=2cm and outer b=2.72a. Dielectric is homogeneous and linear.

    2. Relevant equations


    3. The attempt at a solution
    I tried like this U=∫E*dl but since i know exact value of Emax and no data for εr and Qmax i can't solve this.
     
  2. jcsd
  3. Jun 12, 2015 #2

    berkeman

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    Staff: Mentor

    The part I bolded looks like a typo -- is it?

    The breakdown voltage will depend on the breakdown voltage of the dielectric and the spacing between the conductors. If you have the maximum electric field and the separation (and the dielectric constant), you should be able to calculate the breakdown voltage.
     
    Last edited: Jun 12, 2015
  4. Jun 12, 2015 #3
    I dont know what you mean, bolded part is correct b=2.72a, that's the given value. I don't have the value for the dielectric constant, if i had i could easily find Qmax and then find U using E expressed with Qmax. The problem is that i don't have dielectric constant.
     
  5. Jun 12, 2015 #4

    berkeman

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    Staff: Mentor

    Oh, I see now. The outer radius is given as a multiple of the inner radius -- that's what was confusing me about the dimensions.

    The rest of the question is a bit confusing as well. Is there a figure that you can post? What does it mean when it seems to say

    That makes no sense unless the dielectric constant is the same as free space. Is the problem copied word-for-word?
     
  6. Jun 12, 2015 #5

    It's not completely filled with dielectric, it's filled with dielectric to the some point and rest is free-space.
     
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