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Homework Help: Finding equivalent capacitance

  1. Sep 21, 2010 #1
    1. The problem statement, all variables and given/known data


    http://img819.imageshack.us/img819/1172/capd.th.gif [Broken]

    Find equivalent capacitance
    answer is 4C/3

    2. Relevant equations
    whatever is in parenthesis is subscript
    formula1: series: 1/C(eq)= 1/C(1) + 1/C(2) + 1/C(3) + ...
    formula2: parallel: C(eq)=C(1)+C(2)+...

    formula3: V=Q/C

    3. The attempt at a solution

    because of symmetry I decided that 3C has 0 charge (0q) and that top part has same voltage as the bottom part

    charge split top and bottom equally

    so I solved the problem "as if" 3C doesn't exist
    so on the top series I get C/3 (using formula 1) and C/3 for bottom as well since it's in symmetry
    and top and bottom form parallel so I get
    2C/3 using formula 2

    which is only half the answer

    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 21, 2010 #2


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    Homework Helper

    For top branch 1/Ceff = 1/C + 1/2C = ?
  4. Sep 22, 2010 #3
    o thanks for pointing that out, I made simple algebra mistake ^^
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