Find value of capacitance C?

  • #1

Homework Statement


The equivalent capacitance of the capacitors shown in Figure 21-41 is 9.22 microFarads. Find the value of capacitance C.


Homework 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.

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?
 

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Answers and Replies

  • #2
142
14
3 parallel circuits, which are 7.22 microFarads, ((4.25C)/(4.25+C),and 4.92.
I would calculate that again (there's an error here). Look at the circuit carefully.
(btw. you SHOULD get 2,558microF)
 
  • #3
Delta2
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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)))
 
  • #4
CWatters
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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"
then
"4.25 in parallel with" the above
then
"C in series with" the above
etc

However this bit..
((4.25C)/(4.25+C),
suggests you did
"C in series with 4.25"
or something like that.
 

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