How does electric current flow through a conductor

  • #1
AlphaLearner
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There's been a discussion going on since this following thread: Range of frequency of electromagnetic wave how electric current flow through a conductor. I need a proper clarity, does the electrons literally displace and flow or just the disturbance/energy travel through conductor making electrons just vibrate in their positions back and forth?
If electrons flow, won't the atoms in conductor turn unstable leading it to disintegration/collapsing of conductor itself?
 

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  • #2
UsableThought
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There's been a discussion going on since this following thread: Range of frequency of electromagnetic wave how electric current flow through a conductor. I need a proper clarity, does the electrons literally displace and flow or just the disturbance/energy travel through conductor making electrons just vibrate in their positions back and forth?
If electrons flow, won't the atoms in conductor turn unstable leading it to disintegration/collapsing of conductor itself?

I am not an EE, nor even especially well educated in electromagnetism (esp. the mathematical models); but I reviewed the comments in that previous thread, including yours, and my impression is you are consistently mixing DC "apples" with AC "oranges" when you phrase your questions.

In addition, many of your questions would routinely be answered in any decent textbook; e.g. your question "If electrons flow, won't the atoms in conductor turn unstable leading it to disintegration/collapsing of conductor itself" wouldn't even be a question if you had read a good passage on how electrons behave in conductors. So I have to guess that you either haven't consulted such a textbook, or if you did, you found it confusing or inadequate in some way.

You did in fact mention a textbook in the previous thread - https://en.wikipedia.org/wiki/Concepts_of_Physics by Verma. You cited an analogy he gives (a rather common analogy, in one form or another) of visualizing electrons in a conductor as persons in a tight queue at a movie theater, such that one person knocking into another can start a very fast chain reaction, even though the movement of an individual person is not that fast. However this analogy, though useful, plays a very limited role and isn't anywhere near sufficient by itself. I would expect Verma to provide thorough accounts of current, both verbal and mathematical; and for both AC and DC, making clear the distinction. Have you read all he has to say? Is there something you feel he has left out, or part of his explanation that puzzles you? Since the book is not available outside India, perhaps you could summarize what he has to say about current, and indicate where you feel it's lacking or puzzling?

The reason I make this point about textbooks is that although persons here have repeatedly given you clear answers, you seem to be having trouble seeing these answers in a larger context where they would make sense. It's like trying to put together a jigsaw puzzle when people have given you several pieces, but you don't have enough other pieces to put them against. So it might be helpful both to you & to persons trying to help you here if you could give an indication of what you actually have read or studied about current & what your present "picture" of current is.
 
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  • #3
Drakkith
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If electrons flow, won't the atoms in conductor turn unstable leading it to disintegration/collapsing of conductor itself?

Nope. Atoms themselves are held together by the attraction the electrons feel to the nucleus. Taking electrons away from an atom does not reduce this attraction and the atom remains stable. The bonds between atoms in a conductor are quite complicated and consist partly of localized bonds between adjacent atoms along with delocalized bonds due to an "ocean" of free (shared) electrons in the material. Electric current consists of the net motion of these free electrons and their motion does not lead to any instability since they are free to move about (and already are) anyways.
 
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  • #4
UsableThought
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FYI, to add to my previous comment, I just pulled down off my bookshelf what I think is an excellent non-academic book on electronics; it has a very long "Theory" chapter early on, with a good physics-based perspective, clearly explained, with sufficient mathematics, yet without the math being too daunting for persons who haven't yet studied calculus. They introduce voltage first, then proceed to current; and in discussing current they go into detail about exactly the sort of questions you have raised both here & in the previous thread, including a brief tour of electron behavior at the quantum level. And every decent university level academic textbook I've looked at will give similar explanations. So there is no point in not reading first about this stuff; it is all there to be learned.

The non-academic book I mention above is Practical Electronics for Inventors; I have the 3rd edition, but there is a 4th edition out. It is a big, heavy paperback, lots of content for not that much money - $26 U.S. on Amazon U.S., or ₹2,500 on Amazon India. I recommend it if you are looking for a book on electronics with a solid yet practical EM background; but even just the theory chapter might be useful, as it goes a bit quicker (even considering the excellent depth) than some academic books.
 
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  • #5
AlphaLearner
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Thank you @Drakkith and @UsableThought for putting your time and effort to make me understand such complex thing at least to an extent. The thing is our current education system and even pattern of questioning for competitive examinations for engineering courses is mainly focusing on application of knowledge than just simply knowing it. To apply, than understand how physics works, we are being made to understand how formula works... That's why over 90% of students in our country simply throw off international standard books like 'Principles of Physics' aside and rely on all other physics books written by local authors which trains us up to writing an exam by giving a list of just formulae and apply them. But HC.Verma is a good one. No complaints regarding it.

What guidance would you people like to give me. I feel, I am not like most of physics students as mentioned above. I want to understand physics as a subject.
 
  • #6
AlphaLearner
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HC.Verma has explained all things pretty clearly. But under the drift speed, he said negatively charged are free flowing electrons and positively charged make up the lattice. When electrons flow, they hit the positively charged lattice and said 'positively charged will vibrate back and forth in their positions' and then, negative ones get deflected with greater speed into different direction... So can I conclude that there is both oscillation as well as flow of particles in a conductor carrying electric current?
 
  • #7
UsableThought
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Thanks for clarifying your situation - that makes things clear.

I am not the person to help you, as I'm not an engineering student but only an amateur who likes to tinker with electronics & do some limited self-study. It sounds like you might get the best ideas from members here who are themselves engineers and/or engineering students, whether in India or elsewhere. So I do have one suggestion: Start a new thread (yes, again, sorry!) with an appropriate title & opening post, specifically on this question, and post it in the "Academic Guidance" forum. I think you'll get a lot more replies that way.
 
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  • #8
AlphaLearner
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Start a new thread (yes, again, sorry!) with an appropriate title & opening post, specifically on this question, and post it in the "Academic Guidance" forum. I think you'll get a lot more replies that way.
No problem, that's just a part I said it like that... main focus on the current topic. I think if any further discussion go... look at the next one...
 
  • #9
Drakkith
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So can I conclude that there is both oscillation as well as flow of particles in a conductor carrying electric current?

You can, but this oscillation has nothing to do with the discussion in the previous thread about waves and their relation to electric current.
 
  • #10
AlphaLearner
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You can, but this oscillation has nothing to do with the discussion in the previous thread about waves and their relation to electric current.
Done, Thanks for help. Now the thread can be closed.
 
  • #11
Drakkith
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Done, Thanks for help. Now the thread can be closed.

Why would we close the thread?
 
  • #12
AlphaLearner
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My doubts for now have been clarified.
 
  • #13
Drakkith
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My doubts for now have been clarified.

Others may have questions though, so the thread will stay open for them. :biggrin:
 
  • #14
AlphaLearner
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Oh! Didn't mind about it. Sorry for my selfishness! Even I told I have no doubts for 'now' who knows? A new one arise next.
 
  • #15
AlphaLearner
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Nope. Atoms themselves are held together by the attraction the electrons feel to the nucleus. Taking electrons away from an atom does not reduce this attraction and the atom remains stable. The bonds between atoms in a conductor are quite complicated and consist partly of localized bonds between adjacent atoms along with delocalized bonds due to an "ocean" of free (shared) electrons in the material. Electric current consists of the net motion of these free electrons and their motion does not lead to any instability since they are free to move about (and already are) anyways.
So far, we discussed in solid/liquid conductors. But how about gases? What about cathode - ray tube filled with low pressure hydrogen? Things as you said can't be imaginable here right? How electron stream hit from cathode to anode directly? I understand, it requires a huge force to drive those electrons (High potential)
 
  • #16
Drakkith
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So far, we discussed in solid/liquid conductors. But how about gases? What about cathode - ray tube filled with low pressure hydrogen? Things as you said can't be imaginable here right? How electron stream hit from cathode to anode directly? I understand, it requires a huge force to drive those electrons (High potential)

Gases consist of individual atoms or molecules that are, on average, separated by huge distances (relative to the size of the atom or molecule). There are essentially no bonds between these gas particles and so current cannot flow at all unless unless one of two things happen:

1. The electron is given enough energy to overcome the work function of the cathode and then is propelled through a near-vacuum to anode.
2. The voltage is high enough and the gas dense enough that the electric field partially ionizes the gas and a plasma is formed. This plasma is an excellent conductor and readily conducts electrons from the cathode to the anode.

Also, note that the previous posts have only talked about solids. Liquids are often very different and the exact way that current flows through a liquid depends on that liquid's own properties. For example, a liquid metal conducts current in a different manner than saltwater, and some liquids, especially certain oils, are excellent insulators.

See here for more information on conduction in liquids and solids: http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1163&context=physicskatz
 
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  • #17
UsableThought
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The voltage is high enough and the gas dense enough that the electric field partially ionizes the gas and a plasma is formed. This plasma is an excellent conductor and readily conducts electrons from the cathode to the anode.

Another instance of conduction via plasma is . . . lightning! From the Wikipedia article on lightning:
A typical cloud to ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of 5 kilometres (3.1 mi) tall, from within the cloud to the ground's surface. The actual discharge is the final stage of a very complex process.

Etc. etc. More generally, Wikipedia's article on plasma states:
. . . Based on the surrounding environmental temperature and density either partially ionised or fully ionised forms of plasma may be produced. Partially ionised plasma is popularly understood, for example, as bright neon signs or lightning storms,[6] while more fully ionised plasma is associated with the interior of the Sun,[7] the solar corona,[8]and stars.[9]

And here is a very weird mention of plasma from Benjamin Crowell's free physics textbook Light and Matter, talking about how to properly use an ammeter - vs. how to improperly use it:
Virtually the only circuits whose resistances are significantly less than that of an ammeter are those designed to carry huge currents. An ammeter inserted in such a circuit can easily melt. When I was working at a laboratory funded by the Department of Energy, we got periodic bulletins from the DOE safety office about serious accidents at other sites, and they held a certain ghoulish fascination. One of these was about a DOE worker who was completely incinerated by the explosion created when he inserted an ordinary Radio Shack ammeter into a high-current circuit. Later estimates showed that the heat was probably so intense that the explosion was a ball of plasma – a gas so hot that its atoms have been ionized.
 
  • #18
Drakkith
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And here is a very weird mention of plasma from Benjamin Crowell's free physics textbook Light and Matter, talking about how to properly use an ammeter - vs. how to improperly use it:

Oh, if you could only see some of the safety videos I've had to watch during my military career...
People have been squashed, Humvees have been driven off of the side of 2-story tall ammunition storage structures, bombs have been dropped from 15 feet in the air, Humvees have been driven into aircraft, and more. o_O
 
  • #19
AlphaLearner
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Ionizing gas and forming plasma means creating a path of either positive charged or negative charged atoms making current flow easily along it... Am I right?
 
  • #20
Drakkith
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Ionizing gas and forming plasma means creating a path of either positive charged or negative charged atoms making current flow easily along it... Am I right?

Ionizing the gas creates a plasma consisting of positively charged atoms mixed with negatively charged electrons. Under the application of an electric field, the atoms will move one way through the plasma and the electrons will move in the opposite direction. At the surface of the electrodes, electrons can easily escape the metal and move into the plasma, allowing current to flow through both the plasma and an external circuit connected to the plasma.
 
  • #21
UsableThought
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People have been squashed, Humvees have been driven off of the side of 2-story tall ammunition storage structures, bombs have been dropped from 15 feet in the air, Humvees have been driven into aircraft, and more

Years ago I read a very sad anecdote from a wonderful (but also very sad) memoir about being an Army chopper pilot in Vietnam, Chickenhawk. The author recounted something he (and many others) witnessed one day while off-duty: The crew of a maintenance Huey decided to transport a rotor blade . . . by hanging the rotor by one end, to a cable in turn hung below their chopper. A pendulum effect developed and the rotor they were carrying flipped up to hit the rotor their lives depended on. If I remember the passage right, the crash was fatal.
 
  • #22
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  • #23
AlphaLearner
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Ionizing the gas creates a plasma consisting of positively charged atoms mixed with negatively charged electrons.
Oh! Both of them! Now got a clear idea. Thanks again!
 
  • #24
AlphaLearner
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A pendulum effect developed and the rotor they were carrying flipped up to hit the rotor their lives depended on. If I remember the passage right, the crash was fatal.
After hearing 'Ho-Chi Minh's' trail during US - Vietnam war, I thought Vietnamese were one of the smartest people in world. Hearing this news, shows their foolishness too! But what can even they do when a situation like that occurs. Cant say anything. And please stick to topic. I see @UsableThought a person of knowledge and passion for learning! Same does apply to even @Drakkith!
 
  • #26
sophiecentaur
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If electrons flow, won't the atoms in conductor turn unstable leading it to disintegration/collapsing of conductor itself?
No one has cleared this up so I will introduce the concept of Metallic Bonding. The majority of elements are Metals. In a metal the atoms all contribute one electron to the general pool of 'free' electrons that drift around in the spaces. Each electron is attracted to all the positive nuclei in its vicinity. This is what keeps the metal together and it accounts for the fact that you can distort a reasonably pure metal and the force holding it together doesn't give up. The electrons can move pretty freely from place to place and have no particular 'love' of any individual atom. Metals conduct electricity well as a consequence (and also heat because of their free movement)
 
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  • #27
AlphaLearner
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What could be the maximum length, plasma can be formed. Because @UsableThought says even lightning strike happens through plasma. Then clouds are too high and distant compared to cathode ray tube. So greater electric potential energy can cause greater distance?
 
  • #28
AlphaLearner
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Each electron is attracted to all the positive nuclei in its vicinity. This is what keeps the metal together and it accounts for the fact that you can distort a reasonably pure metal and the force holding it together doesn't give up.
Your reason is pretty near to one of my textbooks I referred. In that he said positive ions make up lattice of conductor and negative charged can freely move... Got the answer!
 
  • #29
UsableThought
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What could be the maximum length, plasma can be formed. Because @UsableThought says even lightning strike happens through plasma. Then clouds are too high and distant compared to cathode ray tube. So greater electric potential energy can cause greater distance?

Hey, it's not original to me - I got it by reading!

Anyway, I do remember from my past reading that each lightning bolt that we see evolves through an extremely rapid incremental process. As a layperson, I would inclined (maybe incorrectly) to view the air between clouds and Earth as a dielectric; as we know, dielectrics can be broken down by a high enough charge. When this happens (I just refreshed my memory with some quick reading), very small channels called "stepped leaders" quickly progress step-wise downward from clouds toward earth; these bring with them huge negative electrical potential. Eventually this potential is brought close enough to attract positive potential from the Earth upward as "streamers"; leaders & streamers meet; and that is when the big lightning strikes occur that we see with the naked eye. Lots of info online about this, ranging from highly technical journal articles to basic "explainers"; here is one explainer article, from NOAA: http://www.srh.noaa.gov/jetstream/lightning/lightning_max.html
 
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  • #30
AlphaLearner
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Hey, I don't say it - an article I cited says it!

Anyway, I do remember from my past reading that each lightning bolt that we see evolves through an extremely rapid iterative process. As a layperson, I would inclined (maybe incorrectly) to view the air between clouds and Earth as a dielectric; as we know, dielectrics can be broken down by a high enough charge. When this happens, very small channels called "stepped leaders" quickly progress step-wise between clouds & earth; these bring with them electrical potential. Eventually a completed channel is available; and that is when the big lightning strikes occur that we see with the naked eye. Lots of info online about this, ranging from highly technical journal articles to basic "explainers"; here is one explainer article, from NOAA: http://www.srh.noaa.gov/jetstream/lightning/lightning_max.html
Whoa! Plenty! So these dielectric are not only manmade but in this case even exist naturally. I should study a bit about dielectrics. But I was able to understand to an extent. Thank you!
 
  • #31
UsableThought
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So these dielectric are not only manmade but in this case even exist naturally.

Again, I am no expert, but yes, I just double-checked and the term apparently is used for materials or combinations of materials found in nature, as well as the innards of capacitors and so on. Wikipedia's article on electrical breakdown says this explicitly in the section on breakdown of gases: "Electrical breakdown occurs within a gas (or mixture of gases, such as air) when the dielectric strength of the gas is exceeded."
 
  • #32
AlphaLearner
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After reading the article from Wikipedia, It looks like how water ionizes polar solvents, getting clearer picture. Water surrounds positive ions with its partially negative 'O' or negative ions with its partially positive 'H' and block their movements. Same can apply here but positive surrounded by negative charges. And water is best solvent due to high dielectric constant of 80! I used chemistry to make understanding more easier.
 
  • #33
AlphaLearner
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I got clarity! So we can consider air not as insulator but as dielectric. Great research done by @UsableThought I have even got clarity how current flow through gases...
 
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  • #34
sophiecentaur
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Your reason is pretty near to one of my textbooks I referred. In that he said positive ions make up lattice of conductor and negative charged can freely move... Got the answer!
This lattice of +ions would fly apart if it were not for the electron gas shepherding them together. So the electrons have several jobs!
 
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  • #35
AlphaLearner
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This lattice of +ions would fly apart if it were not for the electron gas shepherding them together. So the electrons have several jobs!
So both hold each other hand in hand mutually
 

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