Does Voltage Work Against Electron Movement?

[kjeldsmark]

At this page http://amasci.com/elect/vwatt1.html it says:

VOLTS x COULOMBS = JOULES It takes energy to push some charge against the voltage pressure

"against the voltage" I don't understand this. Isn't voltage pro-active with regards to the movement of the electrons? How come it says 'against'?

Thank you

 

[jbriggs444]

From the point of view of a battery driving charge through a circuit, it is pushing the charge carriers upstream against a potential difference.

This is similar to, for instance, the water pump at an amusement park pumping water to the top of the log flume ride. You are pumping water from the pond at the bottom to the spout at the top and letting the water flow down the flume and into the pond. Water = electrons. Pond at bottom = low potential. Spout at top = high potential. Flume = rest of the circuit.

 

[kjeldsmark]

Thank you, this helped on my reflections.

The thing is that I am translating these articles into Danish.

He takes a version of ohms law and writes it out into words. And regarding these words: is the explanation off when it says "against the voltage pressure"? I mean: I would've said: it takes energy to push some charge against/through electrical resistance(/ohms).

 

[sophiecentaur]

At this page http://amasci.com/elect/vwatt1.html it says:

VOLTS x COULOMBS = JOULES It takes energy to push some charge against the voltage pressure

"against the voltage" I don't understand this. Isn't voltage pro-active with regards to the movement of the electrons? How come it says 'against'?

Thank you

The problem about this statement is that Voltage is not a 'pressure'. It is a difference in energy so why does he bring in a false mechanical analogy? Volts are the Work needed to move charges between points with different Electrical Potential. The sign of the Work / Energy (i.e. put in or taken out) will reflect whether energy is being supplied (from a battery etc.) or used (through a resistor or charging a battery). Everyone has an initial problem in assigning the +- signs to the emfs and PDs in circuits when trying to use Kirchoff's Laws. I think he is adding confusion in this statement.
That article is not, on the whole, too bad and he is tries quite successfully to make a number of electrical terms and quantities more approachable. (I have read an awful lot worse!) However, you will need to be very careful in translating technical idioms and metaphors between languages and the best way will be to refer constantly to what the Maths of the situation is telling you - so that both verbal explanations fit the Maths accurately.

It's worth while (as you are getting into the education business) to make clear just what Ohm's Law actually says and not to use the rather sloppy way it is so often used used. Ohm's Law specifies the condition of constant temperature, for instance, and it refers to metals, which behave linearly. There will always her a ratio of Volts and Current for other electronic component but 'Resistance' is only the ratio for a particular combination and can't be relied on any other time.

 

[kjeldsmark]

The problem about this statement is that Voltage is not a 'pressure'. It is a difference in energy so why does he bring in a false mechanical analogy? Volts are the Work needed to move charges between points with different Electrical Potential.

The whole purpose of these Electricity Articles (as I understand) is to teach people what is going on in the real world (the physical concepts, and without much math really(and also the math is simple!). And in science it seems to me students will often need to learn simplified concepts (sometimes even leaving out relevant information) to first build a solid picture and later modify the whole thing. So: the goal is to get a gut-level understanding of so called electricity since many (even engineers) is lacking this understanding (although they might master the math perfectly).


What do you think of the specific phrasing "against the voltage pressure"? Are the charges not flowing AGAINST the resistance/ohms? The energy help the electrons move AGAINST the resistance/ohms? I don't understand why the article says 'AGAINST the voltage pressure'? As if the electrons move along in spite of the voltage pressure-force?

 

[kjeldsmark]

That article is not, on the whole, too bad and he is tries quite successfully to make a number of electrical terms and quantities more approachable. (I have read an awful lot worse!) However, you will need to be very careful in translating technical idioms and metaphors between languages and the best way will be to refer constantly to what the Maths of the situation is telling you - so that both verbal explanations fit the Maths accurately..

These articles are probably the best texts on electricity I've ever read, and thousands of people have visited the amasci.com site because of them.

The reason that I want to translate the material is that a lot of the same misconceptions occur in Danish. There's the same problem with the word electricity in Denmark/Danish. Also, just a couple of weeks ago my teacher tried to teach me that the individual electrons are themselves carrying the energy from the battery to the lightbulb and afterwards they are empty of energy. Explanations like this one are widespread ALSO AMONG TEACHERS! So, I would be glad if we could get rid of these wrong ideas.

However, you are right that one has to be careful when translating texts like this one. Also a few physicists will go through my Danish versions of the articles to make sure that I haven't misinterpreted any terms.

 

[sophiecentaur]

The whole purpose of these Electricity Articles (as I understand) is to teach people what is going on in the real world (the physical concepts, and without much math really(and also the math is simple!). And in science it seems to me students will often need to learn simplified concepts (sometimes even leaving out relevant information) to first build a solid picture and later modify the whole thing. So: the goal is to get a gut-level understanding of so called electricity since many (even engineers) is lacking this understanding (although they might master the math perfectly).


What do you think of the specific phrasing "against the voltage pressure"? Are the charges not flowing AGAINST the resistance/ohms? The energy help the electrons move AGAINST the resistance/ohms? I don't understand why the article says 'AGAINST the voltage pressure'? As if the electrons move along in spite of the voltage pressure-force?

I understand his intention and, as I said, he does a fair job but why associate voltage with pressure when he could just as easily associate it with work or energy? He has obviously been careful in his use of words in order not to be a hostage to fortune and here is an example where he just hasn't done it so well.
I must say, I find it tiresome that people expect to get the higher concepts in certain areas of Science with a "Gut Feeling". How can they be so presumptuous? Could you possibly get a clue about higher Maths by 'gut feeling'? (For some reason, that stuff is never undersold; I wonder why?) How about Carbon Chemistry, without learning about bonding? There is a serious risk in dumbing down in these matters. People ask for a "Physical reason" for certain phenomena when what they really mean is a 'mechanical' model that will explain things. there is no good mechanical model for electricity. It is what it is. By all means make it approachable but don't chuck the baby out with the bathwater.

This is not actually essential in many cases. The so-called child-centred learning can do more harm than good - particularly with able kids who will never be presented with anything 'hard' until long into their education. They are just not used to dealing with 'too difficult'. It is possible to teach nearer the truth as long as you use the right words and avoid the future cognitive dissonance just when students need to make the big steps.

 

[sophiecentaur]

These articles are probably the best texts on electricity I've ever read, and thousands of people have visited the amasci.com site because of them.

The reason that I want to translate the material is that a lot of the same misconceptions occur in Danish. There's the same problem with the word electricity in Denmark/Danish. Also, just a couple of weeks ago my teacher tried to teach me that the individual electrons are themselves carrying the energy from the battery to the lightbulb and afterwards they are empty of energy. Explanations like this one are widespread ALSO AMONG TEACHERS! So, I would be glad if we could get rid of these wrong ideas.

However, you are right that one has to be careful when translating texts like this one. Also a few physicists will go through my Danish versions of the articles to make sure that I haven't misinterpreted any terms.

'Entry level', I think you mean.
Yes - but not talking with a quasi water flow analogy and not by talking about pressure.
You seem surprised about "TEACHERS" not teaching well. You would be amazed at many teachers know anything of Physics but are called upon to deliver it to GCSE level students ( up to 16 years old)

 

[kjeldsmark]

I must say, I find it tiresome that people expect to get the higher concepts in certain areas of Science with a "Gut Feeling". How can they be so presumptuous? Could you possibly get a clue about higher Maths by 'gut feeling'?

It seems to me that you talk in abstract terms. If a person doesn't have a clear understanding of electric current and electric energy in a simple circuit (what is physically going on), and he/she gets this concept corrected and then is able to make sense of things - then I would say there is a pretty good chance that he/she will attain a better/more real "gut feeling".

However, this has nothing to do with my question.

My question is:
What do you think of the specific phrasing "against the voltage pressure"? Are the charges not flowing AGAINST the resistance/ohms? The energy help the electrons move AGAINST the resistance/ohms? I don't understand why the article says 'AGAINST the voltage pressure'? As if the electrons move along in spite of the voltage pressure-force?

 

[sophiecentaur]

Is there a "clear understanding", without considerably more basic knowledge?
Could you not be undervaluing the whole thing? That tricky little 'understanding chemical' flows through the bloodstream when we think we've go something sussed can be so misleading. Science, based on gut feelings will let you down very soon.
To follow your analogy a bit. When you push against a spring, are you "pushing" in the same way as you would "push" against friction? Are the two 'resistance' forces the same? What is happening to the energy in each case? Energy rules, usually and it's not that hard to get familiar with.
Sorry for so many questions but I am demonstrating how the energy situation is far more relevant than the simple force situation. Likewise for charging a battery or capacitor or causing a current in a resistor. You have more or less made my point for me. A gut feeling can just as easily lead to the wrong conclusion as the right conclusion.

Electricity is abstract. It is not a good idea to think it isn't.

 

[kjeldsmark]

If you do not have an answer or comment to the specific question I pointed out, and which this thread is about, then do not comment.

 

[alva]

At this page http://amasci.com/elect/vwatt1.html it says:

VOLTS x COULOMBS = JOULES It takes energy to push some charge against the voltage pressure

"against the voltage" I don't understand this. Isn't voltage pro-active with regards to the movement of the electrons? How come it says 'against'?

Thank you

If the charge is moving against the voltage -> [a (-) charge is moving from + to -] OR [a (+) charge is moving from - to +]. So it takes energy.

 

[alva]

Is there a "clear understanding", without considerably more basic knowledge?

Electricity is abstract. It is not a good idea to think it isn't.

Energy and charge is all you need to define voltage, no matter if you are a 14 y.o. student or a great physicist.
¿What do you mean by "more basic knowledge"?

 

[AlephZero]

He takes a version of ohms law and writes it out into words. And regarding these words: is the explanation off when it says "against the voltage pressure"? I mean: I would've said: it takes energy to push some charge against/through electrical resistance(/ohms).

I think the problem is trying to describe this in terms of "cause and effect", and taking voltage as the "cause".

Certainly there is a correlation between energy, movement of charge, and electrical resistance. That is what Ohm's law says. But as alva said, "voltage" is really defined in terms of an electrostatic field and the work done to move a charge from one place to another. Analogies like "pressure" that somehow make "voltage" an independent quantity are wrong, at a fundamental level, even if they are sometimes useful teaching aids.

If you move a fixed quantity of charge "through" a resistance, you have to do work. You have to do more work if the resistance is higher.

So if you move the charge in the same amount of time (constant current), the voltage across the high resistance is higher, and because of the way we measure the quantities, Ohm's law says the voltage is proportional to the resistance, of course.

Or, if the voltage stays the same, you can only move the charge more slowly (lower current) if the resistance is higher.

 

[sophiecentaur]

Energy and charge is all you need to define voltage, no matter if you are a 14 y.o. student or a great physicist.
¿What do you mean by "more basic knowledge"?

Yes, exactly. You need to be familiar with using the concepts of Energy and Charge - both of which are pretty sophisticated and are very far from water flowing / pressure / mythical electrons moving like tiny peas through a tube. This is my whole point. The 'basic knowledge' is not actually included in the things that people assume you need to have before 'understanding Electricity'.
I have talked to very few 14 yo students who could discuss what charge or energy actually 'are' and even fewer who would know that 1V = 1J/C. That is only served up to them in the first year of Sixth form (17 yrs +)

 

[sophiecentaur]

Anyone who thinks Electricity is easy enough for 'anyone' to understand, should do an experiment on the first person they meet in the pub, shop or work place. Draw a simple potential divider circuit and ask them how it works. Even those of you who work with electrical engineers may find some surprising results.
Electricity is damned hard stuff to understand.

 

[kjeldsmark]

Reminder: the quoted sentence is one single phrasing out one rather long article.

Maybe I haven't been clear: it's not that I don't understand ohms law, voltage, energy or current (basically). It's about the phrasing of:
VOLTS x COULOMBS = JOULES It takes energy to push some charge against the voltage pressure

I see what you mean, AlephZero, with cause and effect, and obviously the terms are very much interrelated. You NEED ohms and current to have voltage and so forth. To me the phrasing gives the impression that the voltage-pressure/force is holding the electrons back and that they move along in spite of this force? The guy is a physicist and an engineer so I just wondered if I was missing some point.

 

[sophiecentaur]

Actually, you only need Potential for Volts to 'exist'. I realize this is a bit chicken and egg but if you start with Volts then they could be generated in any way you like (charges or induced emf; battery or transformer). Then the rest will follow.
If you start the 'chain of causality' with Charge, then you need a different approach for a changing current. Yes - you could make it work but I don't think it would be very satisfactory.
The energy situation (or you may like to think of the Field) is the primary thing here. Once you introduce some charges, they will move at a rate determined by the nature of any path you provide. This path may either involve supplying energy (charging a battery) or dissipating energy (through a resistor).

I just wondered if I was missing some point.

I think that, unlike in most of the document, he actually doesn't do such a good job at that point. Which is why you were thrown a bit. I wouldn't mind betting that he would be prepared to revisit that passage and re-word it in his usual clear way.

 

[kjeldsmark]

Actually, you only need Potential for Volts to 'exist'. I realize this is a bit chicken and egg but if you start with Volts then they could be generated in any way you like (charges or induced emf; battery or transformer). Then the rest will follow.
If you start the 'chain of causality' with Charge, then you need a different approach for a changing current. Yes - you could make it work but I don't think it would be very satisfactory.
The energy situation (or you may like to think of the Field) is the primary thing here. Once you introduce some charges, they will move at a rate determined by the nature of any path you provide. This path may either involve supplying energy (charging a battery) or dissipating energy (through a resistor).


I think that, unlike in most of the document, he actually doesn't do such a good job at that point. Which is why you were thrown a bit. I wouldn't mind betting that he would be prepared to revisit that passage and re-word it in his usual clear way.

You're right, the field is the primary thing. I was obviously wrong saying you need both ohms and current (so to speak). But you do need resistance right? To have an e-field? If there were no electrical resistance between the two poles of the e-field it would just neutralize itself, yes?

 

[sophiecentaur]

You're right, the field is the primary thing. I was obviously wrong saying you need both ohms and current (so to speak). But you do need resistance right? To have an e-field? If there were no electrical resistance between the two poles of the e-field it would just neutralize itself, yes?

That's a funny way of putting it, I would say. The potential is only dependent upon the value of a resistance in a roundabout sort of way. If you start with an ideal voltage source, the presence of a resistor has no effect on potential at all - there might be a modification of the field in the vicinity of the resistor but only if it's resistance is non-uniform. You are right that a Zero resistance between two points would force the PD across them (from a real power source) to be Zero - but that is an extreme / idealised case, like an irresistible force or an immovable object and should be treated with great care.

Why would the field 'neutralise itself' without a resistor? You can get substantial fields in a vacuum. You may be putting the cart before the horse here. Read a few google hits on fields, volts, resistance etc. and see the order these things are usually stated in. It may solve it for you.

 

[kjeldsmark]

I see. Thank you.

"Voltage is equal to the work done per unit charge against a static electric field to move the charge between two points."

Also at wikipedia it says "against a static electric field".

(Thanks for already trying to explain this to me). I just don't get this 'against'. How about:
it takes energy to push some charge THROUGH the voltage pressure

Sent from my iPhone using Physics Forums

 

[kjeldsmark]

Does 'against' mean the same thing as 'towards' in this case?

 

[sophiecentaur]

I see. Thank you.

"Voltage is equal to the work done per unit charge against a static electric field to move the charge between two points."

Also at wikipedia it says "against a static electric field".

(Thanks for already trying to explain this to me). I just don't get this 'against'. How about:
it takes energy to push some charge THROUGH the voltage pressure




Sent from my iPhone using Physics Forums

I don't see why the word 'static' is used for the electric field, as if it's exclusive. Fields can be induced by accelerating charges and, as Potential is the line integral of the field, there can be work involved in all cases. Wiki is not gospel and will chop and change in some nuanced matters.

If you use the term Potential Difference, when you are trying to be precise, it carries with it a specific Sign. When The PD increases, there is more energy available to move charges from + to -. This is the same as you would describe what happens with a vehicle on a hill when you are giving a height difference - you would refer the difference to the start level and to the start point of the moving charges.

Pressure is a poor word to use, too. It's just as much a tension or a thrust, if you really want involve force. Volts are just not pressure so there's only confusion if one equates the two ideas. (Especially when yu are trying to get your head round this in a reliable way).

As for whether you should use 'with' or 'against', I should just say that 'with' is when you are getting energy out and 'against' is when you get energy out. Charges go 'with' the field when energy is delivered to a resistor and 'against' when energy is being put into a battery or 'inside' a source of emf, where a chemical reaction is separating charges and causing + to move out of the + terminal (prior to falling downhill to the - terminal).
There are advantages in thinking in terms of Energy (PD /Volts) rather than Field.

PS I am beginning to get the impression that you may be just a tiny bit chicken about actually committing yourself one way or the other, as to what to think, in case you are wrong. I suggest you decide on one particular way and then see if your chosen model gives the right answer in a case where the reality is obvious. I don't think you are gaining much more by asking what is, effectively the same question several times and getting the forum to say if your view is right. It really doesn't matter if you are wrong - in the privacy of your own mind and notepad - if you end up getting it right.

 

[kjeldsmark]

hm, I'm not sure if I have succeeded in explaining my qestion correctly.

Thank you for your willingness to help.

 

[sophiecentaur]

Is this just a matter of the use of some English words?

 

[kjeldsmark]

Maybe. I simply cannot understand why one would use this word 'against'. The em-energy flows almost instantly down through/along both wires to the load, and energy is consumed. This energy is needed to move the electrons (through the conductor and it's resistivity). The voltage makes the carge flow, so how can it flow/move 'against' it at the same time. Is the voltage making the flow and slowing it down at the same time? This makes no sense to me.

 

[sophiecentaur]

I think you want this to be too 'mechanical'. I also think you would rather believe the (approximate) words than the (precise) formulae. Like Tonto, you should follow the signs.

 

[kjeldsmark]

That's abstract. I feel certain that one should be able to describe what's happening. It's not magic.

 

[sophiecentaur]

You are wanting a metaphor. That's too much to expect in some cases, I think. You really should not look upon Maths as a poor substitute. It is a truly wonderful descriptive language and not a hurdle.

 

[Crazymechanic]

A wonderful language it might be but a language is useless if the other person doesn't understand it.

 

[sophiecentaur]

A wonderful language it might be but a language is useless if the other person doesn't understand it.

By not learning the language one is excluding oneself from the bigger picture. I think it is unreasonable to demand what is, in effect, an inadequate translation in a language that can't handle the concepts. If it's a matter of lack of ability then, as in Premiership Football and Instrumental performance then we sometimes have to accept our limitations and be satisfied that we can't get it completely.
If Maths were not necessary, why is it always resorted to when the Science gets hard? There is not always an arm waving alternative - particularly when a 'precise' explanation is desired.

 

[Crazymechanic]

maybe our whole educational system is flawed , poeple are different I have seen some talented people and really wise yet they don't know nothing of maths , which pretty much renders them useless in hard core science.Yes a scientist may lack intuition or some other stuff which renders him doomed in some other areas.
We are trying to push everyting into everyone to make them kinda all wise to a certain level , I agree that basic maths is training the mind yet I do believe all things shouldn't be applied to everyone at the same level or amount.

just like a famous stand up comedian once said , we are very different the stuff that one drinks may totally kill the person sitting right next to him and vice versa.
Maybe the OP too should rethink how far does one who is not going to be an electrician or something similar , how far does a person like that needs to undersand electricity?
Maybe we should explain the deep stuff only to those who are capable and willing to understand it and then we shouldn't create all kinds of silly analogies and stuff.
I'm not trying to put someone down rather just a suggestion.

 

[sophiecentaur]

@Crazymechanic
I would agree with most of that. The education system (and its political masters) could be a lot better. For a start, it could admit that everyone is not a potential expert in everything. That goes for the media in general and the shame is that there are many clever Scientists who may be good in their Scientific Field but they have no idea of the scientific potential of an average member of the public.
Between them (School, TV and Experts) they manage to present a picture of Science that is way over-trivialised and 'accessible to all'. Not surprisingly, the recipients of this presentation think that it's only a matter of saying a few words and they will, potentially, get anything. It usually fails. I am quite the reverse. I assume that "it" is going to be too hard until I have seriously investigated it and learned a significant extra chunk of knowledge. Very few people just pick things up.

You are totally right about the horses for courses thing, too.

 

[jartsa]

I see. Thank you.

"Voltage is equal to the work done per unit charge against a static electric field to move the charge between two points."

Also at wikipedia it says "against a static electric field".

(Thanks for already trying to explain this to me). I just don't get this 'against'. How about:
it takes energy to push some charge THROUGH the voltage pressure

Two equally good definitions of voltage:

1) Voltage is equal to the work done per unit charge when something moves the charge between two points, against the charge's will.

2) Voltage is equal to the work done by unit charge when the charge fights its way from point A to point B, against some resisting force, like friction, inertia or gravity.

 

[kjeldsmark]

sophiecentaur: I'm not asking for at metaphor, but a description.

jartsa: yes, and how would you then interpret this:

VOLTS x COULOMBS = JOULES It takes energy to push some charge against the voltage pressure

here it doesn't say 'against resisting force' but 'against voltage pressure'? This is, to my understanding, two completely different things.