What Exactly is Alternating Current

sophiecentaur

It's interesting to note the contrast between the quote and the response in the above post. The use of 'electrons', which is in the quote (noname2020x) is totally ignored in the response (Low-Q). Clearly, the response is from someone who has more knowledge of electricity and realises that bringing electrons into the topic really doesn't help.

I wonder if the message has sunk in yet. It may be possible to give some sort of limping explanation for DC using electrons but trying to take them with you to into AC explanations (and the way that transformers and synchronous motors work, for instance) is fruitless.

Crazymechanic

@sophiecentaur : By that visualizing I meant as close as possible to the model physics knows the best.It's not like one just hears a word and then makes a totally self sustained story out if it atleast not in my case. It's rather you read the most accurate theory to date and try to grasp it , ofcourse there will be some misconceptions from person to person I guess that's just human nature.It's like 10 persons traveling down the same road with the same map and still after the trip everyone will have a slightly different account of how the road looked like and what was there.Same in physics and even worse as the things are much more complicated and in the case of electricity- hidden from the naked eye.
Ah the photons , let's be honest understanding all these things can be compared to the world's economic situation , there will be rich people there will be middle class and there will be poverty and homeless people not to go into detail it's just the way things are because of how we live how much we understand and want to do.Same in physics if someone understand something good then that isn't a sign that some other will understand those things even close.
The only responsibility to those who know is to spread the knowledge as unedited and close to the truth as possible.

@Low-Q:"adding to what you just said is that nowdays DC lines are starting to evolve as we have high power thyristors and all kinds of "smps" equipment to step up or down even high voltages of DC and to then invert those to usable AC mains.
A German company "ABB" and "Siemens" are currently building such high power DC 800kv lines in China.

http://http://www04.abb.com/global/s...technology.pdf

@By the way "sophiecentaur" is right because in electrical equipment there are very rare times when something from the quantum level of physics needs to be considered like electrons for example of photons in EM vawe, so when it's not needed we can survive with the classical laws of electricity that we all know better of like Ohm's, ampere's and others.Each level of competence has certain things you need to know but not more, like a guy who repairs tv sets probably doesn't know quantum mechanics good or even at all but that doesn't make him a bad repairmen I guess as long as he is in his field of expertise.

sophiecentaur

My point is that the model / visualisation of electrons circuits that most people carry in their heads (due to what they're bombarded with at School and on TV) is damagingly flawed and leads them to seriously wrong conclusions if and when they start to think about it independently. It's not merely inadequate; it's bad, imo and it really has no place in PF discussions - or even the discussions in secondary schools. It's nowhere near the 'closest model'.

Back to photons: The picture that people (yer average Jo public) have of photons is a throwback to the old Corpuscular Theory of light that went out about 400 years ago. So much for Science education.

Crazymechanic

As much as I recall there were some good threads here on PF about the electron/electricity topic and some people with advanced knowledge explained those things pretty well I'm not saying this should be the topic whenever someone wants to wire a light bulb in his garage but if someone really is interested in what he learns he can find not only tv and public misconceptions but also good info to read.
And thanks "sophiecentaur" for your effort as being one of those who rings the bell everytime some wrong or misunderstood words and theories come up.
Let's keep up the good work.

zoobyshoe

I don't see how this improves anything at all since:

http://en.wikipedia.org/wiki/Ampere

If you try to talk about a flow of charge and or current, that charge and or current automatically refers to a specific number of electrons passing a point per unit time, by definition. I don't think the model of electrons moving along the wire is the idiosyncratic and personal model you make it out to be. It's a standard definition of current as far as I can see. Therefore, your correction completely confuses me.

sophiecentaur

Of course there's no question that Current is Charge per unit time and that implies the net transfer of electrons in many or even most cases. But current doesn't always involve electron movement, for a start.
Are the sub atomic distances travelled by electrons for high frequency AC really a suitable way to describe what goes on? The actual speed (mean drift speed) of the conduction electrons and the distances travelled will depend upon the geometry (thickness and length of wire, for instance) and also the metal involved - do you want to bring that into each description? Is it relevant? What has any of that got to do with the operation of a circuit?

Just what is the problem with using the quantity Current? It is, I admit, a slightly more abstract concept than peas flowing in and out of the ends of a pipe but electrons aren't actually like peas in a pipe in any case.

How would you use the concept of electrons flowing when describing the situation in a Capacitor or a Radio Antenna? Current, on the other hand, gives you a seamless join between the wires, the fields and the waves so why not accept that it's clearly the way forward. I seems to me like a bit of inverted intellectual snobbery at work when people insist on using an elementary and flawed model in preference to a far more appropriate one.

zoobyshoe

Current means electron flow. It's a current of electrons (except in the case of ions). Therefore it should not be considered wrong to speak of electrons moving in one direction or another. It's confusing to me that you're insisting that one term for the same thing is vastly superior to another. If the electrons only move some subatomic distance in high frequency AC, for example, so too does the current only move some subatomic distance. Likewise if we speak of charge. Everything wrong with electron flow has to be equally wrong for current and charge because current is electron flow and electrons are charge. Such is the definition every text gives me, anyway. It sounds like you're saying, "We can speak of traffic but talking about the motion of cars on streets is inverted intellectual snobbery." The word "current" doesn't banish the image of a bunch of electrons moving through a wire, or vibrating back and forth in it, from my mind. Neither does "charge".

I have three fat modern 1st year physics texts here among my books and all three maintain that when you have current it's because electrons are moving generally in one direction under the influence of an electric field. Two of them go into meticulous detail about this motion being only a very slow drift (no peas in a pipe here), I'm sure you'll be glad to hear, but I think it's possible you may be up against just about every textbook there is in insisting that people not think of current, or the motion of charge, as moving electrons.

AC: The current is moving back and forth, the charges are moving back and forth, the free electrons are moving back and forth. All three equally correct, as far as I can see.

sophiecentaur

You are entirely missing my point here. I am not arguing against describing electric current in terms of electrons, of course, because they are the majority carriers in most circuits. But current can just as reasonably be carried in the form of ions, positive electrons or holes (which are all equally valid entities - maybe, just a bit less common). My problem with the free use of the term electron -as if it actually 'explains' anything - is that people who use the term seldom have a clue about what an electron is. They are using the most concrete sounding term that they can lay their hands on rather than admitting that they are dealing with a very abstract concept called electricity. They are using a term which they assume is somehow more fundamental and 'easy' when all they are really doing is reaching for the nearest thing to the 'peas in a tube' model. How does electron flow actually explain anything? Electron motion is a fact but just how relevant is it to a better understanding of 'electricity'? Let's face it, most aspects of the topic were well understood long before Mr Chadwick actually gave us electrons on a plate.

On the subject of textbooks, I would be interested to hear if you could quote an instance where any of your books deal with Kirchoffs Laws, AC theory, Inductors, EM induction and actually mention electrons in those particular sections. I would suspect that even K1 is described in terms of Charge Conservation. Text books discuss conduction through metals in terms of electron motion because it ties in very handily with atomic structure. This is, of course, a very good idea as it links two very different aspects of science. When a text book talks of current in a wire and electron flow it is usually to demonstrate (with actual numbers) just how slow the drift speed is - to lay the ghost of electrons zapping through at nearly the speed of light.

I could leave you with one little thought about Displacement Current, which certainly involves no charge carriers at all but it is necessary if you want to describe alternating (time varying) currents properly. You can, perhaps, neglect it at 50Hz but Maxwell should really be considered if you want to give bomb-proof explanations to unsuspecting students. Use the word 'Current' and they will not come back later and tell you you got it wrong when you gave them the electron explanation.
(See this thread which is running concurrently).

Crazymechanic

I actually understand both of you either @sophiecentaur and @zoobyshoe
But in overall I think @sophiecentaur is right about one thing that in the start someone doesn't need to know what an electron is to learn some basic truths about the phenomenon associated with it.When I was like 7 years old I dismantled old tv sets and put the resistors and tubes in spare part boxes and ofcourse at the time I had no understanding of what was really going on in those parts I just had the love towards those things and I leaned to use the screwdriver and different tools to even get to them in the first place.But as years went on I learned more and more and now I am to the point where I would like to see the flow of electricity in terms of something deeper meanwhile not forgetting the simple most basic facts about the phenomenon as a whole.
I guess one could say it's like when a 5 year old asks his mom or dad what is the thing we call sex you wont go and tell him the whole truth and in the end for better understanding show him some tape or film about it.At that age you will explain this practice in terms of something a child would understand and in the same time that won't affect him badly.
These days there are alot of little kids walking in streets using some rude words and phases and sometimes they don't even know the meaning behind them.
i guess @sophiecentaur is trying to say that we can get into this kind of situation if we try to "dig" too deep with little knowledge and a small showel.

But in the same time I can agree to @zoobyshoe .For the ones who have enough understanding and knowledge why can't they use what they like as long as it's the truth and represents the phenomenon equally or even better.
Ofcourse if we go deeper in terms of current as electron movement of certain amount in a conductor then I guess we have to also speak about the EM field and photons and how that affects the whole fast electricity thing with "super slow" moving actual electrons.Otherwise it would not be the whole picture.
And here I have to admit that even though I have a clue about the EM photon field working hand to hand with the passing of current in a conductor I don't feel so advanced to tell some deep facts about it fully ,well I know them to myself but I am not that sure about them that I could go on and teach others about them.So maybe we should create two threads on PF in which one would be the electricity for beginners with the basic things and the other one would be for the ones that wanna go further.Where all the advanced and complicated phenomenon of quatum physics would be explained.And then when someone has a question judging by the context of the question he could find his answers there.More like a FAQ but in terms of for example "why is electricity fast when electron movement is slow"? I think these kind of questions appear pretty frequently.
Ofcourse if someone of the PF staff thinks that such an idea is meaningful or maybe something similar is already made.

sophiecentaur

You have summed it up quite nicely there. The only point I can add is to say that it is a very risky statement to say that you 'understand' what electrons are when you are not able to 'understand' electricity using classical terms. (that is the general you and not you personally) It may feel as though you are making it more concrete is some sense but, in fact, the electron is an even less concrete concept (if you really consider what it 'is') than the good old electric current which you can at least measure with a meter from the store on the corner.
Particles may seem like your friends but they can (and frequently do) lead you astray.