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Current in Open Circuits

  1. Jan 24, 2011 #1
    1. The problem statement, all variables and given/known data

    Looking at the open circuit demonstrated in figure 2 (see attachment), what is the current through the ammeter? What is the voltage at point p?

    2. Relevant equations

    3. The attempt at a solution

    I am assuming if it an open circuit, I would think that the current would be zero (I might be wrong though). Meaning that since the current is zero, so is the voltage.

    I have a feeling I might be wrong though...

    Any help would be great!

    Attached Files:

  2. jcsd
  3. Jan 24, 2011 #2


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    Staff: Mentor

    What's the voltage across the terminals of a 12V battery that's not connected to a circuit? What current is it producing?
  4. Jan 24, 2011 #3
    Wouldn't the voltage be 12V? However there is no resistance, so using ohm's law: I=V/R, with 0 resistance, that would make the current infinite, which doesn't make any sense...
  5. Jan 24, 2011 #4


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    Staff: Mentor

    With no connection the resistance would be infinite; no conductivity.

    So in your circuit, what's the total resistance between the battery terminals?
  6. Jan 24, 2011 #5
    Well since it is not connected then it would be infinity

    Using my Ohm's law argument that would give us our voltage of 12 volts across the battery

    and 12/inf is approx 0, so the current would read out zero.

    Am I right? If so then thank you so much!!!
  7. Jan 24, 2011 #6


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    Staff: Mentor

    Right; The open circuit dangling off of the positive battery terminal would all be at the battery's potential, and no current would be flowing. By the way, I chose 12V as an example. Check the actual battery voltage specified in your problem.
  8. Jan 24, 2011 #7
    Yeah I noticed that, mine would be 5V :)

    Thank you so much, that makes total sense!
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