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What are the charges on these three capacitors?

  1. Nov 21, 2015 #1
    1. The problem statement, all variables and given/known data

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    3. The attempt at a solution

    Now, they're in series, so I found the equivalent capacitance to be about 0.57 microFarad. And I have technically gotten the correct answer according to the back of the text. The question in the text clearly asks for the charge on each capacitor, but merely gives the answer as 6.9 microCoulomb. Now, I got that answer too just using the formulae available. But my complete answer was that the top capacitor would have +6.9 microCoulomb, the middle capacitor no charge, and the bottom capacitor would have - 6.9 microCoulomb. Is that correct? Or do they all just share the 6.9 microCoulomb charge separation?
     
  2. jcsd
  3. Nov 21, 2015 #2

    gneill

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    Staff: Mentor

    They all acquire the same charge of 6.86 μC. Check: Determine the voltage across each capacitor given this charge on each. What do those voltages sum to?

    Consider that the components are in series, so that any current that flows must be identical for each device in the loop. If some charge Q moves onto the first capacitor's top plate, then Q must leave its bottom plate and be pushed onto the next capacitor in line, and so on.
     
  4. Nov 21, 2015 #3
    So current does flow through a capacitor then? I've read online that people can't agree whether it does or not; that it blocks DC current, which seems to be what is depicted in that picture above.
     
  5. Nov 21, 2015 #4

    phinds

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    Gold Member
    2016 Award

    Current does not flow through a cap but in the surrounding wires until there is a stable distribution of charge. Where did you read otherwise? You should not trust such a source.

    Current WILL flow through a cap if you get dielectric breakdown and thus arcing , but that's an abnormal situation.
     
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