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Grounded conductor and Electric field potential question ?

  1. Dec 11, 2016 #1
    1. The problem statement, all variables and given/known data
    upload_2016-12-11_21-52-59.png







    2. Relevant equations

    V= kq/r.



    3. The attempt at a solution

    For 8-8, I do not really know how to approach it.
    For 8-14 , I think that q2=-q1 and q3=q1+q2.
    I can now use V=kq/r and then find the equations for r>R3 , r=R3 , R2<r<R3 , r=R2 and R1<r<R2 and then graph. Am I right?
     
  2. jcsd
  3. Dec 11, 2016 #2

    Simon Bridge

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    For 8-8 - the question tells you how to approach it.
    Sketch the situation, then, using a dotted line, sketch the potentials for each ball separately.
    Then apply the superposition principle - draw in the result as a bold line.

    For 8-14 - please show your reasoning about the charges, ... ie. what happens to the charge distribution on sphere 2 and why?
     
  4. Dec 16, 2016 #3

    rude man

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    8-14: the "spheres" quoted in the problem are actually shells. There is a central solid sphere or ball of radius R1, then infinitely thin shells of radii R2 and R3.

    There are thus 5 surfaces with respective charge densities (from innermost to outermost): σ1, σ2, σ3, σ4 and σ5.
    σ1 should be obvious. From that, σ2 should be readily calculated.
    That leaves σ3, σ4 and σ5. You can get 3 independent equations in these 3 unknowns. One involving σ4 and σ5 is obvious. One involving σ3 and σ4 should also be apparent; similar idea to σ1 and σ2. For the last equation, force zero E field inside the grounded shell.
    Having all 5 surface charge densities enables you to compute everything else.
    I don't think so. For one thing that would make q3 = 0.
     
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