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Homework Help: Total Capacitance. Parallel or Series?

  1. Mar 27, 2010 #1
    1. The problem statement, all variables and given/known data

    In the attached question about total capacitance of the network, because of the layout I wasn't sure if this should be totalled as capacitors in parallel or capacitors in series.

    I was thinking perhaps parallel, but am not sure.

    Thank you! :smile:


    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
  3. Mar 27, 2010 #2
    :) good way to start is by noticing that you have 4 pairs of capacitors (upper-left,upper-right,lower-left, and lower-right) .. each pair there is connecting in series .. find the equivalent capacitor for each of the four pairs, then replace them with their equivalents .. then what will you notice? can you work fron there (hopefully yes) .. :)


    [NOTE] :
    to figure out whether the two capacitors are in series or parallel :

    1- if they are sharing one end (node) , then they are in series ..
    2- it they are sharing two ends (nodes), then they are in parallel..
     
  4. Mar 27, 2010 #3
    Thanks BigStar,

    so I could do an "in series" calculation on each pair so I have a figure for four capacitors.

    Then with these four figures I could calculate using an "in parallel" calculation...
     
  5. Mar 27, 2010 #4
    you are missing something here!
    correct me if i got u wrong .. are you suggesting that after you get the equivalent capacitors (four of them, one at the up-right, one at up-left, one at low-right, and low-left) you calculate them as if they all were in parallel?
     
  6. Mar 27, 2010 #5
    That's what I had thought, but obviously I'm not taking something into account...
     
  7. Mar 27, 2010 #6
    :( yes that is not correct .. you want to try again?

    lets see what we know and what we have ..

    first, you know that capacitors in series and parallel look something like the following figure:

    http://img175.imageshack.us/img175/66/95306873.jpg [Broken]

    as I mentioned in a previous reply:

    from the figure, lets start with the capacitors in " series ":

    as you can notice, one end from a capacitor is connecting to one end of the other capacitor .. and thats always the case whenever you deal with capacitors in series ..

    what about capacitors in " parallel "? :

    from the figure you can see that one end from a capacitor is connecting to an end of the other capacitor (and thats not just this) also the other ends from the two capacitors are connecting.. and thats how is goes with capacitors in parallel ..


    now we get to your problem .. it looks like the following figure:

    http://img710.imageshack.us/img710/8066/36727868.jpg [Broken]

    ..

    we agreed that, the each of the four pairs is connecting in series .. then your problem will reduce to the following figure :


    http://img185.imageshack.us/img185/6946/94146670.jpg [Broken]


    to this point you are doing a good job .. so now can you tell me what should you do next?

    (** hint **: what if you want to take the two capacitors at the right half together , and the capacitors at the left hand together?)
     
    Last edited by a moderator: May 4, 2017
  8. Mar 27, 2010 #7
    Thanks, yes I understand it now.

    Redraw the circuit with the two 10uF capacitors in series as a single 5uF capacitor. On the left are two 5uF capacitors in parallel, in series with two 5uF capacitors in parallel on the right.

    Redraw the circuit again replacing the two 5uFs in parallel with a single 10uF capacitor.

    There are then two 10uFs in series which is 5uF.
     
  9. Mar 27, 2010 #8
    :) that is exactly the perfect answer ..
     
  10. Mar 27, 2010 #9
    Thanks very much BigStar...!
     
  11. Mar 27, 2010 #10
    ;) welcome ZedCar .. >> (wish me good luck for my midterm tomorrow!)
     
  12. Mar 27, 2010 #11
    Very best of luck...!
     
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