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Equivalent Capacitance

  1. Sep 24, 2014 #1
    1. The problem statement, all variables and given/known data
    In the circuit shown in the figure the voltage of the battery is 15.0 V, and the capacitors have the following capacitances: C1 = 2.32 mF, C2 = 2.25 mF, C3 = 4.85 mF, C4 = 4.89 mF
    What is the equivalent capacitance of the four capacitors?

    http://tinypic.com/r/24dn5oi/8
    Two sets of series capacitors that are parallel to each other

    2. Relevant equations
    Ceq=(1/C1+1/C2+1/C3...)^-1 ---- series
    Ceq=(C1+C2+C3...) --- parallel
    3. The attempt at a solution
    Ceq=(C1+C3)(C2+C4)/(C1+C2+C3+C4)
    =(7.17)(7.14) / 14.31
    = 3.58 mF

    According to online hw system, it's wrong. Is my equation incorrect?
     
  2. jcsd
  3. Sep 24, 2014 #2

    phinds

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    I think you've got the series/parallel actions backwards. Do capacitors add directly when in series or when in parallel?
     
  4. Sep 24, 2014 #3

    CWatters

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    Perhaps show us how you got...

    Ceq=(C1+C3)(C2+C4)/(C1+C2+C3+C4)
     
  5. Sep 24, 2014 #4

    CWatters

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    I don't think that's his problem because his relevant equations..

    ... are correct. Capacitors add in parallel.
     
  6. Sep 24, 2014 #5

    phinds

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    Right, which is what led me to wonder how he got a term (c1+c3)
     
  7. Oct 8, 2014 #6
    Is the answer near 3.13 mF
     
  8. Oct 9, 2014 #7

    NascentOxygen

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    Very close to that, yes.
     
  9. Oct 9, 2014 #8

    phinds

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    Even closer to 3.11 :)
     
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