determine the polarity of capacitors

Discussion in 'Homework Help' started by gbox, Jan 25, 2016.

  1. gbox

    Thread Starter Member

    Dec 29, 2015
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    [​IMG]

    How do I determine the polarity of capacitors?

    My attempt:

    [​IMG]
     
    Last edited: Jan 25, 2016
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Bearing in mind this is your homework, what are your thoughts so far?
     
  3. Papabravo

    Expert

    Feb 24, 2006
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    Not all capacitors have polarity as an intrinsic property. Certain types do have an associated polarity, namely electrolytic and tantalum capacitors. If the schematic symbol does not indicate a polarity, then you can work on the assumption that any of the given capacitors could have either a positive or negative voltage, if the sources were ac sources, which they are not. Your schematic has no DC current paths. Where did you get this problem?
     
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  4. WBahn

    Moderator

    Mar 31, 2012
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    When will you get the hint that you are expected to show YOUR best attempt to solve YOUR homework problems instead of just asking others to work them for you (or to tell you how to work them)?

    Future threads that you start in which you do not show some kind of honest attempt will be locked and/or deleted.
     
  5. gbox

    Thread Starter Member

    Dec 29, 2015
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    sorry, edited
     
  6. WBahn

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    Mar 31, 2012
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    What is you reasoning for each of these? How are we to know that these aren't just random guesses?
     
  7. gbox

    Thread Starter Member

    Dec 29, 2015
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    I started with the left  8V battery and took the left side of C1 to be + and than the right side - and so on
     
  8. WBahn

    Moderator

    Mar 31, 2012
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    So would you have gotten the same results if you had started on the right side?

    If not, does it seem reasonable that the polarity of the capacitors (by which I am assuming you mean the polarity of the charge stored on the capacitors) depends on which end you start with?

    How about analyzing the circuit and determining what the charge is on each capacitor. Won't that tell you the polarity of each?
     
  9. gbox

    Thread Starter Member

    Dec 29, 2015
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    No I get 2 different answers if I look first at the right voltage source or on the left voltage source
     
  10. hp1729

    Well-Known Member

    Nov 23, 2015
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    Do we assume all capacitors are the same type and value? Would it make a difference?
     
  11. crutschow

    Expert

    Mar 14, 2008
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    Assuming you start with discharged capacitors and then apply the voltages, the relative capacitor voltage and polarities will depend upon the relative capacitance value of each capacitor.
    So you need to write node voltage equations for all the nodes that include the capacitor values as variables to solve the problem.
     
  12. WBahn

    Moderator

    Mar 31, 2012
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    Not so much same type (e.g., mylar vs. ceramic), though the leakage will impact the final distribution and we can only assume negligible leakage.

    The relative values will affect the polarity of the charge on a couple of them. An interesting more advanced exercise is to identity those capacitors for which the polarity is known regardless of the values of any of the capacitors.
     
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