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Homework Help: Find value of capacitance C?

  1. Jun 4, 2016 #1
    1. The problem statement, all variables and given/known data
    The equivalent capacitance of the capacitors shown in Figure 21-41 is 9.22 microFarads. Find the value of capacitance C.

    2. Relevant equations
    Ok so this has to deal with Ceq, and it is a combonation of series and parallel circuits. Knowing this, I can use for series 1/Cs=(1/C1)+(1/C2) and so on. For parallel, it is Cp=C1+C2 and so on.

    3. The attempt at a solution
    Looking at the picture, the givens is Ceq = 9.22 microFarads. I first simplify the circuit so that it shows 3 parallel circuits, which are 7.22 microFarads, ((4.25C)/(4.25+C),and 4.92. Setting up the equation, i get C to equal something not 2.56 microfarads. What did i do wrong?

    Attached Files:

  2. jcsd
  3. Jun 4, 2016 #2
    I would calculate that again (there's an error here). Look at the circuit carefully.
    (btw. you SHOULD get 2,558microF)
  4. Jun 4, 2016 #3


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    Not exactly 3 parallel circuits but 7.22 in parallel with (C in series with (4.25 in parallel with (12.0 in series with 8.35)))
  5. Jun 5, 2016 #4


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    That's correct but you have to resolve them in the right order taking into account the brackets eg...

    "12.0 in series with 8.35"
    "4.25 in parallel with" the above
    "C in series with" the above

    However this bit..
    suggests you did
    "C in series with 4.25"
    or something like that.
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