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Homework Help: Find an electric field around a hollow insulating sphere.

  1. Sep 16, 2014 #1
    1. The problem statement, all variables and given/known data
    An insulating hollow sphere has inner radius a and outer radius b. Within the insulating material the volume charge density is given by ρ(r)=[itex]\alpha[/itex]/r,where [itex]\alpha[/itex] is a positive constant. What is the magnitude of the electric field at a distance r from the center of the shell, where a<r<b?
    Express your answer in terms of the variables α, a, r, and electric constant ϵ0.

    2. Relevant equations

    E*4[itex]\pi[/itex]r^2 = Q * volume

    3. The attempt at a solution

    Substituting and integrating with the above formula, I came out with (α/3[itex]\epsilon0[/itex])(r-((a^3)/(r^2)). I cannot tell if the error is with my math, or with the formula I began this process with.
  2. jcsd
  3. Sep 16, 2014 #2


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    Science Advisor
    Homework Helper
    2017 Award

    Hello sport, and welcome to PF.
    Apparently you conclude that your answer is in error. How do you know ?
    You show your answer, but I can't reconstruct what you do to get there...
    Please post some intermediary steps...
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