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Basic capacitor concepts

  1. Jul 10, 2017 #1
    If a capacitor is charged to 10V where the negative side is connected to ground (0V), when the capacitor is disconnected from the power supply on both the positive and negative sides;

    1) Will the negative side of the capacitor still be 0V relative to the ground it was just connected to?

    2) Say the two sides of the capacitor are shorted. Charge would flow from the positive to the negative side of the capacitor, so does this mean the negative side of the capacitor will no longer be the same voltage as the ground it was connected to previously?

    I'm asking this because I have components connected to the negative side of a capacitor that will likely break if the voltage rises too much above ground and although I think I know the answer to this I am really doubting myself now.

    Any help is appreciated, thanks!
  2. jcsd
  3. Jul 10, 2017 #2


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    what other components ? show us the circuit
  4. Jul 10, 2017 #3
    I was just generalising, the actual circuit is higher voltage and I don't have a diagram of it sorry. But for example I know the negative of a 1.5v battery is attached to the negative pin of the capacitor.
  5. Jul 10, 2017 #4
    If those components are lifted together with the capacitor and has no connection to the ground then they will remain on the voltage of that capacitor pin where they are connected, so they won't break down.

    If those components are connected to the ground and the capacitor too, then the capacitor is not actually 'disconnected' from ground: it still connects through those components -> more details needed.
  6. Jul 10, 2017 #5
    ah ok, well despite that what happens in the situations 1) and 2) I mentioned before, ignoring any other components?
  7. Jul 10, 2017 #6


    Staff: Mentor

    The absolute potential of a node depends on the rest of the circuit between the node and ground.

    In circuits, we calculate voltage differences between two points. The absolute potential and the choice of where to connect ground ( if at all) is rarely significant.

    If you are trying to understand circuits and ideal components, you're better off forgetting about ground and absolute potentials. Just remember that a voltmeter has two leads, not one.
  8. Jul 10, 2017 #7

    jim hardy

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    You do realize you're asking people to guess at what you have in mind. Even in "Charades" you have to give better hints than that.

    Do you have a voltmeter and a ladder ? Try it out. One experiment is worth a thousand expert opinions.
  9. Jul 10, 2017 #8
    You are asking a theoretical question - about a real world situation? "the actual circuit is higher voltage"

    I think if you sketch the scenario, and look at how you are going to charge a capacitor - you will find your answer.
  10. Jul 10, 2017 #9
    Thanks guys, yeah my bad, should have included diagrams. I'll try testing myself and see if it makes sense.
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