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Homework Help: Is this a short circuit or not?

  1. May 15, 2014 #1
    My doubt is about the circuit in the picture. The capacitor is charged ans the switch open. There's a voltimeter connected to the terminals of the capacitor.

    Does a current flow through the wires of the voltimeter causing a short circuit? If not, what would happen in the circuit described? What would the voltimeter read??

    I would really like to understand it.

    Thank you very much!

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    Last edited: May 15, 2014
  2. jcsd
  3. May 15, 2014 #2
    Well, actually it could never be a short circuit beacuse the voltimeter has a very high resistance, right? So there is a current and the voltimeter would read 0?

  4. May 15, 2014 #3


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    Staff: Mentor

    An ideal voltmeter presents an infinite impedance (resistance) to what it's measuring, so no current can flow through it. It's as if the voltmeter could "see" the voltage without ever touching the circuit in any way.
  5. May 15, 2014 #4


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    Homework Helper

    What is a short circuit? What is the usual electrical resistance through a short circuit?

    As you say, the voltmeter is designed to have a very high resistance, ideally taken as infinite. Ideally, the current through the voltmeter is zero, but in reality there is a very small current passing through it (necessary for the needle to swing to register the voltage across its terminals). But the current is low enough that you can generally consider it not to affect the charge on the capacitor (even if it discharges very slightly through the voltmeter).
  6. May 15, 2014 #5
    Yes the Voltimeter has a very high resistance so there will be a very small current. The voltimeter will not read zero. It will read the voltage at the capacitor. That's why it's called a voltimeter.
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