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Homework Help: Equivalent capacitance in series/parallel

  1. Jul 27, 2007 #1


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    1. The problem statement, all variables and given/known data

    What is the equivalent capacitance for the following schematic?

    Note that C1 is 11 µF, and C2 is 3 µF.

    http://img511.imageshack.us/img511/8051/questionzi5.png [Broken]

    2. Relevant equations

    [tex]C_{parallel} = C_1 + C_2 + C_3 + ... + C_n[/tex]

    [tex]\frac{1}{C_{series}} = \frac{1}{C_1} + \frac{1}{C_2} + \frac{1}{C_3} + ... + \frac{1}{C_n}[/tex]

    3. The attempt at a solution

    I tried the following:

    1: Considered the four right-hand caps to be in parallel and add them as above, yielding 47 µF, and:

    2: Added that 47 µF cap in series with the remaining 5 µF and 3 µF caps like so:

    [tex]C_{eq} = \frac{1}{\frac{1}{5} + \frac{1}{47} + \frac{1}{3}} = 1.8051 \mu F[/tex]

    But no go (and appropriately so, since the number seems a bit small). Where am I making a mistake?
    Last edited by a moderator: May 3, 2017
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  3. Jul 27, 2007 #2

    Andrew Mason

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    Homework Helper

    The right-most three capacitors are in series. Find the equivalent capacitance of those three. That capacitance is then in parallel with the 4.0 uf capacitor. Find the equivalent capacitance for the parallel part. That is in series with the other two.

    Last edited by a moderator: May 3, 2017
  4. Jul 27, 2007 #3


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    That makes a hell of a lot of sense.

    I've got one remaining shot at this problem, so I would much appreciate it if someone could double-check me on this conceptually (oddly, the number still seems low at first glance, but I'm completely new to caps):

    [tex]C_{rt series} = \frac{1}{\frac{1}{24} + \frac{1}{11} + \frac{1}{8}} = 3.8824 \mu F[/tex]

    [tex]C_{rt parallel} = 3.8824 + 4 = 7.8824 \mu F[/tex]

    [tex]C_{eq} = \frac{1}{\frac{1}{5} + \frac{1}{7.8824} + \frac{1}{3}} = 1.5147 \mu F[/tex]
    Last edited: Jul 27, 2007
  5. Jul 27, 2007 #4
    looks good to me
  6. Jul 27, 2007 #5


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    Thanks for the look-over; 1.5147 is the answer.

    Surprised to see it so low, but it's the answer.
  7. Jun 5, 2011 #6
    somebody help me solve this question please
    find eq capacitance when each capacitoras capaccitance C

    h Untitled.png
  8. Mar 19, 2012 #7
    hi plz anser this
    this is not good see next post

    Attached Files:

  9. Mar 19, 2012 #8
    plz answer this


    Attached Files:

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