Current in Open Circuits

  • #1
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Homework Statement



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?

Homework Equations





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!
 

Attachments

  • Screen shot 2011-01-24 at 11.10.07 PM.png
    Screen shot 2011-01-24 at 11.10.07 PM.png
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Answers and Replies

  • #2
gneill
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What's the voltage across the terminals of a 12V battery that's not connected to a circuit? What current is it producing?
 
  • #3
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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...
 
  • #4
gneill
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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...

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

So in your circuit, what's the total resistance between the battery terminals?
 
  • #5
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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!!!
 
  • #6
gneill
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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.
 
  • #7
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Yeah I noticed that, mine would be 5V :)

Thank you so much, that makes total sense!
 

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