Analyzing Open Circuits: Current and Voltage

[dancergirlie]

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!

 

[gneill]

What's the voltage across the terminals of a 12V battery that's not connected to a circuit? What current is it producing?

 

[dancergirlie]

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...

 

[gneill]

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?

 

[dancergirlie]

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!

 

[gneill]

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.

 

[dancergirlie]

Yeah I noticed that, mine would be 5V :)

Thank you so much, that makes total sense!