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Clarification on an electric fields solution

  1. Jan 20, 2012 #1
    This isn't actually a homework problem. I just had a question about the solution they provided.

    1. The problem statement, all variables and given/known data
    physprob96.png


    2. Solution given in solutions manual
    physsol96.png


    3. My question

    When they convert dE into cylindrical coordinates why does the radius "a" lose its exponent?

    dE = [itex]\frac{\kappa\lambda\delta l}{a^{2}}[/itex] = [itex]\frac{\kappa\lambda\delta\theta}{a}[/itex]

    I have to be missing something simple, I just know it...
     
  2. jcsd
  3. Jan 20, 2012 #2

    SammyS

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    It's because [itex]d\ell=a\cdot d\theta\,.[/itex]
     
  4. Jan 20, 2012 #3
    Does that come from the arc length formula?

    Thank you
     
  5. Jan 20, 2012 #4

    SammyS

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    Yes it does.
     
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