Ohm's law, voltage

  • Thread starter kjeldsmark
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  • #26
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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.
 
  • #27
sophiecentaur
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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. :smile:
 
  • #28
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That's abstract. I feel certain that one should be able to describe what's happening. It's not magic.
 
  • #29
sophiecentaur
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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.
 
  • #30
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A wonderful language it might be but a language is useless if the other person doesn't understand it.
 
  • #31
sophiecentaur
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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.
 
  • #32
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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.
 
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  • #33
sophiecentaur
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@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.
 
  • #34
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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.
 
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  • #35
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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.
 
  • #36
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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.
I interpret it this way:

It takes energy to push some charge to where the charge is unwilling to go, like for example into a place filled with similar charges.


And here are some additional thoughts:

A negative charge wants to go from the minus electrode of a battery to the plus electrode. It takes energy to push the charge the other direction, from plus to minus. Battery happens to push electrons from plus to minus, inside the battery.

In a circuit consisting of a battery and a resistive wire, electron has the most energy at the negative electrode. If electron moves from there into either one of the two possible directions, its energy decreases.

Charges are sensitive to voltage pressure, whatever voltage pressure means. If a charge is effected by a voltage pressure and the charge is pushed, work is being done.
voltage = energy / charge

If a charge is effected by a voltage pressure and the charge moves by itself, work is being done by the charge.
voltage = energy / charge
 
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  • #37
sophiecentaur
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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.
You say you don't want a metaphor but that is a total metaphor. Volts are not pressure so you are starting with a metaphor in that phrase (the two terms just can't go together in a sentence that is self consistent). You may feel a bit defensive about that article - which I agree, is pretty good - but straying away from precise wording in an attempt to make things more acceptable (I don't use the word 'understandable') he has introduced just the sort of confusion that you have here. It can't be surprising when a when a fudge results in a fudge. You should not feel constrained to that article for ever. It has actually let you down in this. Don't throw it away though - this is a demonstration where multiple sources are always needed when you want to get to grips with things. Needless to say, the Maths approach will not let you down that this.

I can see your problem with the notion of charges 'struggling against a force' in a circuit. That problem arises because it's not a good way to look at it. You need to 'push' charges uphill when charging a battery. In the end, this will involve forcing them against the electric field - doing work against the field from the battery, to cause the chemical changes so using the idea of a force is fair enough - if you insist. But your thread title has the word "voltage" in it and voltage is energy. You also could say that you need to 'push' charges through a resistor - on the grounds that the energy dissipated can be likened to a force times a distance. But why not stick to the electrical world and say the energy is Charge times Volts?

You seem to have reached an impasse in this because you appear determined to get over this hurdle on your own terms. Why not take the accepted approach? You are not selling out if you do - you are opening up the next stage. I can guarantee that the new paradigm will only help you.
 
  • #38
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Just to add to my previous post and all that ahs been said after that.
I do think the modern society is actually very dumb and ignorant , let me explain why.Not because we would not know more than we knew some time ago rather because these days we are so interested and obsessed with the feelings that the modern day man needs to be a self contained little genius.Everybody's so " smart" and all knowing these days it sometimes makes me sick just by looking at them.Today it's more about your status than what you actually know , everyone wants to be lawyer , a bank director, a famous nobel prize winning scientist and a King of a country , I too had my classmates dream of big things meanwhikle they were so ignorant to simple learning stuff they couldn't tell their right from their left.
I apologize for telling you all this kjeldsmark but I do think sometimes it's very healty to realize how far one needs to go.
Pick up a thing and ask yourself are you strong enough to lift it if your not then put it back and come to try again after you had some training.I know some sports people , you see when it comes down to physical weight lifting you cannot find a side way with a great analogy or something similar you either have it or you don't , there is no way around.
Nobody comes perfect they all had to sweat and fight alot before they had the power to do those things they do.

As for the thread topic.

jarsta said:
I interpret it this way:
this is the problem when we all come together and each of us interpret it this and that way.In this case i happen to agree with Sophie because if you have a 2+2=4 thing there is nothing to interpret anymore.your either right or your wrong.too bad but this isn;t psychology were we are being teached these days that everyone is right just in his own kind of way , I think such a teaching is destructive to the person hearing it as it leads one into thinking that no matter how wrong you get you can still be right.

And lastly , why are you so obsessed with the against voltage thing? All that matters is that you have voltage which is called PD.It's always some kind of voltage level with respect to a common point of no voltage or lower voltage or whatever different potential at some other point, like a PD across a resistor or across the terminals of a battery.There is no pressure before PD but after you apply a PD you can think of it as a force , the electric field that is associated with the PD which is responsible for " pushing" charges in the wire.Even though pushing may even not be the best word to use here.Now the part where you say that the electric field or voltage pushes against something is the tricky thing here , have you heard os superconductors? in other word say a copper wire at very low temperatures and the current can be there forever , theoretically , so there is no more loss or resistivity so the PD does't have to push agaisnt anything.
I believe the author using the against thing just wanted to show that a PD is doing work but he could have just said that when you have a PD it does a certain amount of work which is proportional to the amount of the PD or volts you have in agiven situation.
 
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  • #39
sophiecentaur
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this is the problem when we all come together and each of us interpret it this and that way.In this case i happen to agree with Sophie because if you have a 2+2=4 thing there is nothing to interpret anymore.your either right or your wrong.too bad but this isn;t psychology were we are being teached these days that everyone is right just in his own kind of way , I think such a teaching is destructive to the person hearing it as it leads one into thinking that no matter how wrong you get you can still be right.
It's nice to know that. It may be a shame that life can't be lived without the Maths and Engineering - which aren't matters of opinion. But people who are posting on this forum are making use of other people's use of those disciplines so they can hardly dismiss them as a nuisance. There's a time and a place for such things and there are other times and places for culture and subjectiveness. The two things do, rather, run counter to each other and we are stuck with the dichotomy.
 
  • #40
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I think the problem is not in how much one understands something , it's rather that these days poeple want to pretend they understand things they have no clue about and maybe they even should't as it's not their deal and they dont even care about it.people like that fuzzy good little feeling inside when you ahev read something and you think oyu now know it ad you almoust go like yes I did it, but then one needs to be subjected to the harsh reality where he is proven or said wrong from a source of authority , we all need a point of reference to understand how far or how good or bad we are without that referance we are unable to understand anything.
I'm not good at maths either , when it comes to quantum mechanics and stuff like that I too understand better by analogies rather than numbers and equations.But atleas I'm fair to myself and don't call myself a quantum scientist.

On the other hand in no way do I want to discourage someone from learning into stuff even if he isn't good at maths , I believe that there can be people who can be good at physics and maybe evne discover something new without being very good at each particular thing ,overall it's not so muhc a question of how good your nature given talents are than a question of how really passionate and devoted one is in trying to reach for the top but not to be proud but for the fun of it and because he likes it that way.The results will show themselves.No hard work can go unseen.
 
  • #41
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I interpret it this way:

It takes energy to push some charge to where the charge is unwilling to go, like for example into a place filled with similar charges.


And here are some additional thoughts:

A negative charge wants to go from the minus electrode of a battery to the plus electrode. It takes energy to push the charge the other direction, from plus to minus. Battery happens to push electrons from plus to minus, inside the battery.

In a circuit consisting of a battery and a resistive wire, electron has the most energy at the negative electrode. If electron moves from there into either one of the two possible directions, its energy decreases.

Charges are sensitive to voltage pressure, whatever voltage pressure means. If a charge is effected by a voltage pressure and the charge is pushed, work is being done.
voltage = energy / charge

If a charge is effected by a voltage pressure and the charge moves by itself, work is being done by the charge.
voltage = energy / charge
Another question for you:

Again, regarding this sentence:

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

Does this sentence imply to you that the charges move because of the voltage force or in spite of the voltage force?
 
  • #42
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the charges move because of the electric field which is a direct result of voltage in a conductor.
PD is applied to a conductor and the charges are now pushed under force towards one or the other direction.before the voltage was applied the charges moved randomly with no net movement in a given direction so there was no voltage in the wire.
As you can tell something made them change that behaviour and move all in one direction to create a what's called current flow.So obviously there is a force involved here and that force is the electric field from the PD you applied to the wire.Is this good enough?

jarsta said
It takes energy to push some charge to where the charge is unwilling to go, like for example into a place filled with similar charges.
that is correct as alike charges repel but in a circuit with a PD , say a resistor connected to a battery you have the +ve and the - terminal , the + charges are wiling to go towards the - ones and to cancel out , so it's rather that a Potential difference is a situation where you seperated charges using energy , and now once you have them seperated you can use them to do work as they will want to get back to that equilibrium situation which is more commonly known as a empty battery.
Yet anyway the seperated charges create a PD and the PD exerts a force on the charges in the conductor which makes them flow one or the other way , instead of zapping around randomly.
So a force is exerted by voltage to the charges if you like it better this way said.
But i wouldn't say theu have to move against anything after that, well they do encounter resistance and some other forces which can arise in devices like transformers etc like inductance but that is a whole different point , the basic thing is yu have voltage and you have it applied over a wire or circuit and you have current and the one is the result of the other.

Don't get mislead by bad wording, many poeple talk about cars and horsepower but few of them actually have a clue of what it actually means and some may even think that there are horses packed in the engine it doesnt change a thing.that is just a word used to describe certain units of power output.
 
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  • #43
sophiecentaur
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Another question for you:

Again, regarding this sentence:

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

Does this sentence imply to you that the charges move because of the voltage force or in spite of the voltage force?
I see where you're coming from now. You can only make a charge move by providing a potential. (You can't poke it with a stick. Lol) so everything happens due to some imbalance of forces ( gradient of potential). Charges respond only to that. Descriptive words like 'with' and 'against' are what are getting in your way again. That's why the Sign in maths is so useful and it is consistent. :wink:
 
  • #44
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Another question for you:

Again, regarding this sentence:

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

Does this sentence imply to you that the charges move because of the voltage force or in spite of the voltage force?

The answer to the question: In spite of the voltage force.


Or if we want to say it correctly: In spite of the Coulomb force q*E (charge q times electric field E)

if we multiply force q*E with distance d we get q*E*d , which is energy
if we divide energy q*E*d by charge q, we get energy per charge which is voltage
 
  • #45
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This thing IS a question of wording. We 'agree' about these basic voltage things.

My question was regarding the specific sentence (which I'm translating), if it says (THE SENTENCE) that the charges move because OR in spite of the voltage pressure/force?
 
  • #46
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Jartsa: thanks. That was for me a concise explaination.

The sentence imply to you that the charges move - in spite of - the voltage force, but this is wrong isn't it? In reality they move BECAUSE of the voltage force right?

So the sentence is wrong?
 
  • #47
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Jartsa: thanks. That was for me a concise explaination.

The sentence imply to you that the charges move - in spite of - the voltage force, but this is wrong isn't it? In reality they move BECAUSE of the voltage force right?

So the sentence is wrong?
That sentence seems correct to me: It does take energy to push a charge against an electric field E, over a voltage E*d.

But before and after that sentence Bill Beaty talks about charges that are NOT being pushed against an electric field, those charges are just "falling" at some terminal velocity in an electric field. That may be some kind of problem. I mean, the reader may become confused.

Actually, maybe it's not impossible that the writer got confused. So maybe there's an error in that sentence, although it's correct.
 
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  • #48
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but the charge moves BECAUSE of the voltage force. When the sentence say the opposite - how can it be correct?
 
  • #49
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I think there is a problem here , jarsta told you about the coulomb force and yes indeed like charges repel, but here we are speaking about a conductor which only serves as the current carying medium , we are not talking about some free floating electrons in a vacuum chamber and even those align themselves to form a current path if a sufficiently high PD is applied, like in a CRT tube.

The conductor about which the OP speaks in a current carrying medium , the PD is the battery or any other power source introduced in the picture, the + charges want to get to the - charges whenever you form a path between the battery terminals , so what has that to do with the coulomb repulsion between electrons? We can observe that current is made in the wire when closing a circuit , and if that wire is cooled to low enough temperatures the current flow become resisatnce free.

Why would the charges need to be pushed agaisnt the very own field which made their flow possible in the first place?
You have a PD , you have a wire you connect the wire to form a cirucit , current flows , it doesnt flow against anything , would you say that a river flows against hill? The river flows from the highest place read potential to the lowest place /potential...
 
  • #50
sophiecentaur
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but the charge moves BECAUSE of the voltage force. When the sentence say the opposite - how can it be correct?

In the context you are seeing, it is not correct. It is badly put. The best thing you can do is just to let it go.
That statement would apply of you charged up a ball and we're moving it in the field between two plates. You would then be able to move the charge against the force caused by the field. In a purely electrical set up charges only move with the field. + charges will move to a lower electrical potential. To charge a battery, you need a source of higher PD than the battery is producing. Charge will then flow down into the battery - against the emf of the battery. The current that flows will be the difference between the two voltages / any resistance in the circuit. There! I even managed to get the word 'against' into my description.
 

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