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Gauss's law:E vs r graph (two cases of shell)

  1. Sep 21, 2015 #1
    1. The problem statement, all variables and given/known data
    Ok.Then there was a question
    If r is distance measured from center of a charged shell and R is it's radius then the graph which may correctly represent variations of electric field is

    images?q=tbn:ANd9GcTAWn-2hPoxdlZtV7zw5hQR8h-1MLTVoShJoGQsmJrwd6ebbsTfVw.png
    media%2Fca6%2Fca6b7881-725e-43c3-b5be-88eb8fb653a9%2FphpPh04vU.png

    2. Relevant equations
    E vs R graph

    3. The attempt at a solution
    The answer is given to be A but I want to ask why not C ?There are two cases
    1-shell with all charges on surface in this case E for r<R is zero so Option A fits in
    2-Shell with charges throughout the volume(volumetric distribution)
    In which E for r<R has formula
    E=ρr/3ε0 (ρ=CHARGE PER UNIT VOLUME)
    it is clear E ∝ r
    For this C seems correct.And the question does not clarify which type of shell(type 1 or type 2) is to be referred
    So why answer is A?Why it can't be C?
     
  2. jcsd
  3. Sep 21, 2015 #2

    blue_leaf77

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    "Shell" is usually intended to mean an infinitesimal (limit-zero thickness) surface.
     
  4. Sep 21, 2015 #3
    so no volume ?nearly 2d?
     
  5. Sep 21, 2015 #4

    blue_leaf77

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    Yeah, no volume. The shell alone has no volume, but of course it encompasses certain volume inside it.
     
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