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 Feb 16th 2011, 10:29 AM #1 Junior Member   Join Date: Jan 2011 Posts: 9 voltage What does it mean the therm "voltage" in electric circuit? I know the definition, but I still can not understand anything rely. I know also that this is the difference in electric potentials, but every point in circle should have a different voltage. And that does not make sense. (since there is r in the formula for potential, and every point of the circuit have different r from voltage source). And, how can happens that voltage can drops?
Feb 16th 2011, 11:29 AM   #2

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 Originally Posted by kapital What does it mean the therm "voltage" in electric circuit? I know the definition, but I still can not understand anything rely. I know also that this is the difference in electric potentials, but every point in circle should have a different voltage. And that does not make sense. (since there is r in the formula for potential, and every point of the circuit have different r from voltage source). And, how can happens that voltage can drops?
First of all the term "voltage" is not, in my opinion, a good word to use. I prefer the more correct term "potential drop."

In any event the term voltage is commonly used and unambiguous at least. You have a voltage in any place that there is an electric field. It is one way of representing the energy (gained or lost) of a charged particle in an electric field.

The potential difference across a perfect conductor is zero. That means the charged particles traveling along them neither gain nor lose energy. If the current flows into an insulator (or a material that is not a perfect conductor), aka a resistor, the potential "drops" across the resistor. This is due to the fact that the charges cannot flow freely through the resistor. Some energy is lost and the charged particles lose some energy. This lost energy usually goes into effects such as heating the resistor. The lost energy is represented by the loss of voltage (ie a potential difference) across the resistor.

I'm not sure what you mean by "...but every point in circle should have a different voltage. And that does not make sense. (since there is r in the formula for potential, and every point of the circuit have different r from voltage source)." What is r? And what circle are you talking about?

-Dan
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 Feb 16th 2011, 07:47 PM #3 Junior Member   Join Date: Dec 2009 Location: MN Posts: 14 Are you referring to the potential due to a charge defined as k*q/r. If you are, I believe this takes place inside the source (battery) and is how you have a 12v battery or etc.. Inside a circuit, potential is not being created no more but being used to move the charge around.
 Feb 17th 2011, 04:32 AM #4 Junior Member   Join Date: Jan 2011 Posts: 9 Thanks for all answers. The potential difference across a perfect conductor is zero. That means the charged particles traveling along them neither gain nor lose energy. If the current flows into an insulator (or a material that is not a perfect conductor), aka a resistor, the potential "drops" across the resistor. This is due to the fact that the charges cannot flow freely through the resistor. Some energy is lost and the charged particles lose some energy. This lost energy usually goes into effects such as heating the resistor. The lost energy is represented by the loss of voltage (ie a potential difference) across the resistor. What does that actually mean? Not in a physical formulas mean, but what happens with the electrons? Do they move more slow? Is it less of them? Or what?
Feb 17th 2011, 02:39 PM   #5

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 Originally Posted by kapital Thanks for all answers. The potential difference across a perfect conductor is zero. That means the charged particles traveling along them neither gain nor lose energy. If the current flows into an insulator (or a material that is not a perfect conductor), aka a resistor, the potential "drops" across the resistor. This is due to the fact that the charges cannot flow freely through the resistor. Some energy is lost and the charged particles lose some energy. This lost energy usually goes into effects such as heating the resistor. The lost energy is represented by the loss of voltage (ie a potential difference) across the resistor. What does that actually mean? Not in a physical formulas mean, but what happens with the electrons? Do they move more slow? Is it less of them? Or what?
Electrons, by and large, do not flow through a conductor or insulator as such. The do move, I'm not trying to tell you that they don't, but it's more of a "pushing" phenomenon. And electron enters, say, a conducting wire and it pushes one out of the far end. Eventually the original electron will pass all the way through the wire, but we waited for it to get through the whole way it might take several seconds (or minutes depending on how large the conductor is).

I might not be explaining this well. Perhaps looking at it this way might clear some confusion: the potential acting across the wire affects all the electrons at once, moving them along.

Either way you want to look at it if we are talking about an insulator the electrons are harder to "move" like this. So you get heating aka resistance in the wire.

-Dan
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