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Electric field at a distance greater than the radius of sphere

  1. Apr 3, 2013 #1
    1. The problem statement, all variables and given/known data

    A solid ball of radius rb has a uniform charge density ρ.

    What is the magnitude of the electric field E(r) at a distance r>r_b from the center of the ball?

    2. Relevant equations

    E(r) = (Q/ε)*1/Area

    3. The attempt at a solution

    If Q=ρrb

    and Area = (4/3)πr3,

    then E(r) = [itex]\frac{ρrb}{ε*(4/3)*πr3}[/itex]


    However,
    the correct answer is in the image attached.
    E(r)= =%5Cfrac%7B%7B%5Crho%7D+%7Br_%7Bb%7D%7D%5E%7B3%7D%7D%7B3+%7B%5Cepsilon%7D_%7B0%7D+r%5E%7B2%7D%7D.gif
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Apr 3, 2013 #2
    Area is not (4/3) pi r^3

    Also, Idon't think q = prb
     
  4. Apr 3, 2013 #3
    Oh. I get it now. Thanks!
     
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