Why would voltage decrease over a resistor?

[Naty1]

mpatryluk...
in case you are still around...and I would not blame you based on the discussion so far if you gave up...
I assume you are starting out with electrical circuits, and if so the discussions so far probably haven't helped much.

I don't understand 3/4 of the drivel posted so far...sophiecentaur being the exception.
I would paraphrase his comments as saying "Such a model [posted by others] of charge distribution, integrals, Gauss' law,etc, are unnecessarily abstract in a circuit analysis like this." At least that's what I think. I'll stick with what I posted already, but here are some additional ways to think in more concrete terms...maybe less abstract than I posted...

why voltage changes along a resistor:

think of voltage as the difference in electric potential energy of a unit charge, one electron, say, transported between two points. [That potential difference comes from some source, say, electro chemicial [battery] or maybe a dc generator. For a chemical viewpoint, you can look up stuff like 'redux reactions' or 'battery', say via Wikipedia.]

These individual electrons are what move along in lock step in a typical conductor...and resistor...loosly bound electrons, called 'conduction electrons', 'valence electrons' or whatever, in a conductor, more tightly bound electrons in a resistor...'More tightly bound' means a stronger local bond to an atom or other material structure...so it takes more potential [electrical energy] to dislodge them.

[An insulator, like ceramic or rubber or plastic has really tightly bound electrons and will not let them move easily...electrons can't move, so they resist any current flow because their electrons 'stay in place'. Circuit designers like insulators because they don't waste power! ]

think of circuit electrons in this simplified analogy as maybe cars lined up on ahighway...as you move one, then two, then three, as moving along in a resistor, it takes more and more work to overcome friction, analogous to individual electron attraction in a typical resistor...So as you move your voltmeter further and further apart over the length of a resistor to measure voltage, you encounter more and more displaced electrons, each with a tiny electric potential difference, and they each add up.

But this has nothing to do with any 'distribution of charge'...the same number of electrons entered one end of the resistor as emerged from the other end...each moves along like a line of cars on the highway...individual electrons 'drift' from atom to atom rather slowly, but as one enters, another leaves at a distant point, pushed along by the potential difference of all the intermediate electrons.

So while electric current is really fast overall, but not light speed, individual electrons in a typical circuit bump along at a only few meters per second...it's called 'electron drift velocity' like cars stuck on a highway moving slow, like 10mph in heavy traffic, yet one enters and one exits miles apart giving the appearance of rapid transport.

Hope that helps...

 

[Delta Kilo]

What was it that set up the original Charge distribution in the situation described? Surely it was energy put into the system and established the Potential Energy situation.

This is an extremely vague statement which does not provide any description at all of the physics behind it.
How is "Potential Energy situation" established exactly? What is the physical mechanism?

This is not just a 'chicken or egg' argument. There is a inherent order of cause and effect.

There is a n inherent order of cause and effect, but it is in reverse to what you seem to be implying. The formula for the voltage I gave above is not limited to steady-current state. Shall we look at transients in RC circuits then?
There the causal link is clear: charges determine the electric field (voltage, if you like) -> electric field exerts forces on the electrons -> current flows -> charge distribution changes gradually over time.

That would come from the PD and the length of the resistor .

Sorry but this is tautology. PD is just another characteristic of electric field. It describes it, it does not cause it to appear. Where did the PD come from then?

Like in mechanics one can solve problems using Newton's laws ans forces or use Lagrangian and principle of least action. The two approaches are equivalent. Some problems are better suited for one or the other. In some cases forces help you to understand the picture qualitatively while quantitative answer comes from Lagrangian.
Your position seems to be like dismissing the forces as completely irrelevant.

 

[sophiecentaur]

@DK: I clearly haven't been writing my ideas clearly enough. I was trying to be general. rather than vague. The charges got there because some work was done on them. That was all I meant by the "potential Energy Situation". (I have made several posts here and I assume that, if someone is going to challenge one of them, they could read -or at least skim - the others, for context.)
Of course there is a direct relationship between Energy and Field. It's just that there are times when it's more useful to consider one than the other. In the case of electrical circuits it is common (pretty well universal) to use Volts. Discussions of the operation of some components will often use fields (Antenna theory, as an example) but I don't t think you could give me examples where Fields are used for overall circuit calculations. That paper about charges and fields around a circuit was interesting and 'confirming' but it doesn't actually suggest that we should alter the way we do our analysis . Nor does it say anything about what's 'really' happening. On that matter, I don't see that we have any serious disagreement.

My main reason for getting into this was to challenge the statement (way back - and I've forgotten who it was who actually made it) that the Charges are the prime cause of current flow. Which charges are at work inside a transformer or a radio receiving antenna? All the theory I have been taught says that there are emf's involved, which induce currents. No charges move through space between primary and secondary windings or between transmitter and receiver. However you want to describe the way of a battery works, it would be very inconvenient if you were to say that you should treat the way a resistor works when connected to a battery differently from when it is connected to a transformer. Is this not why we use Volts in most analysis. I just realized that the notion of a Current Source is sometimes used, in which case you could say, I suppose, that the Coulombs per Second are what drives its load - but even then, it's not Coulombs that are used, it's rate of charge flow.

I (and you, also) will continue to use PD as the 'explanation' for the driving cause of what goes on in electrical circuits. We all know that, because it's the pragmatic way. So, although there are alternative ways of 'looking at' the situation, they won't affect what goes on in practice.

 

[rcgldr]

My main reason for getting into this was to challenge the statement (way back - and I've forgotten who it was who actually made it) that the Charges are the prime cause of current flow.

It was proably my post, and I did not mean to imply it was the prime cause, or that is should be used as a basis for studying circuits. I was just trying to offer an alternate explanation for voltage drop across a resistor, using charge (density) diferential at the terminals of a battery, as an alternative to voltage, hoping that it might seem a bit less abstract to the OP.