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Homework Help: Relative permittivity

  1. Jun 3, 2015 #1
    1. The problem statement, all variables and given/known data
    I've been given a question where I have to find the electric field strength at a point between two charges. Now I understand the mathematics but the question I'm trying to solve says two point charges of value 2C and 3C are position within a medium of relative permittivity 5.5.

    My question is when i put my values into the electric field strength equation should this value 5.5 be multiply by the permittivity of free space or be used differently.

    2. Relevant equations

    3. The attempt at a solution
    I have looked on the internet for the formula but sometimes its written differently and I just want to be one hundred percent confident I'm using this value correctly since I keep finding conflicting information.
  2. jcsd
  3. Jun 3, 2015 #2
    It is strange that it's worded like that, but my guess is that you multiply the permittivity of free space by 5.5
  4. Jun 3, 2015 #3


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    Staff: Mentor

    Hi Jmphysics. 2d4066413017023.gif

    εo and εr always go around together like a married couple; where you find one it needs the other right alongside.

    Some formulae emphasise this by explicitly showing their product εoεr, other formulae denote this product concisely as just ε
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