How does electric current flow through a conductor

[AlphaLearner]

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?

 

[UsableThought]

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.

 

[Drakkith]

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.

 

[UsableThought]

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.

 

[AlphaLearner]

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.

 

[AlphaLearner]

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?

 

[UsableThought]

Thank you @Drakkith and 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.

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.

 

[AlphaLearner]

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...

 

[Drakkith]

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.

 

[AlphaLearner]

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.

 

[Drakkith]

Done, Thanks for help. Now the thread can be closed.

Why would we close the thread?

 

[AlphaLearner]

My doubts for now have been clarified.

 

[Drakkith]

My doubts for now have been clarified.

Others may have questions though, so the thread will stay open for them.

 

[AlphaLearner]

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.

 

[AlphaLearner]

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)

 

[Drakkith]

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

 

[UsableThought]

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.

 

[Drakkith]

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.

 

[AlphaLearner]

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?

 

[Drakkith]

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.

 

[UsableThought]

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.

 

[Drakkith]

If I remember the passage right, the crash was fatal.

 

[AlphaLearner]

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!

 

[AlphaLearner]

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!

 

[Drakkith]

And please stick to topic.

My fault! Sorry!

 

[sophiecentaur]

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)

 

[AlphaLearner]

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?

 

[AlphaLearner]

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!

 

[UsableThought]

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

 

[AlphaLearner]

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!

 

[UsableThought]

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."

 

[AlphaLearner]

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.

 

[AlphaLearner]

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...

 

[sophiecentaur]

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!

 

[AlphaLearner]

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

 

[AlphaLearner]

Finally came to a conclusion. There's nothing separate like an 'Insulator' and 'Dielectric'. Every insulator is dielectric. Every insulator has some degree of tolerance against electron flow no matter its state of matter is... That degree of tolerance is measured as volt/meter, Number of volts the current has between electrodes displaced by 1 meter. This even show smaller insulator requires some voltage to break through it and make current pass through it. The same insulator with larger length require much more larger voltage to pass through it . A cathode ray tube require over 10,000 volts to make electric current pass through gas over a few centimeters. But a lightning strike requires over 100 million volts to pass through a few meters of air. (Of course, gas in cathode ray tube is hydrogen and air is a mixture of gases so materials in both cases are different).
How could this be anywhere linked to resistivity in electron flow? Is it possible? Will a property like this even exist in conductors but of less/negligible value? Is this what the measure resistivity for them is?

 

[Drakkith]

How could this be anywhere linked to resistivity in electron flow? Is it possible? Will a property like this even exist in conductors but of less/negligible value? Is this what the measure resistivity for them is?

I'm not sure if you're asking about the dielectric properties of the conductor or the resistivity of the conductor.

 

[AlphaLearner]

I'm not sure if you're asking about the dielectric properties of the conductor or the resistivity of the conductor.

I am just asking will both have a link? Is resistivity is nothing but the possession of dielectric character even in a conductor? Or both are completely different?

 

[Drakkith]

I am just asking will both have a link? Is resistivity is nothing but the possession of dielectric character even in a conductor? Or both are completely different?

Resistivity and polarizability (which is essentially what determines how good of a dielectric a material is) are both properties of a material, but I don't know if they are linked to each other. I would think that the answer is no, but I don't have the necessary knowledge to give you anything more than a guess,

 

[AlphaLearner]

All I know regarding resistivity of conductor is property of resisting flow of electrons and has various factors like area of cross - section, material of wire, temperature... But will what resists this flow of electrons is mainly the possession of partial dielectric character which depend on material of conductor is what struck in my mind for a while...
I am questioning regarding how far the conductivity of a good conductor is affected by this property.
Or diectric property has nothing to do with it... Anyone?

 

[UsableThought]

Is resistivity is nothing but the possession of dielectric character even in a conductor? Or both are completely different?

Resistivity and polarizability (which is essentially what determines how good of a dielectric a material is) are both properties of a material, but I don't know if they are linked to each other. I would think that the answer is no, but I don't have the necessary knowledge to give you anything more than a guess,

To the extent I am capable of saying anything sensible here, I agree with Drakkith. Essentially there are differences at the atomic & quantum level between materials that are good conductors, vs. good insulators; and this also applies to semiconductors. So it wouldn't seem safe to assume that a term useful for discussing insulators (e.g. dielectric) shares its meaning in some way with a wholly different term (e.g. resistivity) that is useful for discussing conductors. It's not a bad question to ask, however - especially if considered as an incentive to do more reading!

It is easy to find articles online that bring up this sort of thing - e.g. https://www.halbleiter.org/en/fundamentals/conductors-insulators-semiconductors/ - but to me this is the sort of question where nothing is going to replace some dedicated reading of textbooks that explain all of this thoroughly. Trying to learn it in bits & pieces doesn't seem like it will be profitable.

 

[Drakkith]

I am questioning regarding how far the conductivity of a good conductor is affected by this property.
Or diectric property has nothing to do with it... Anyone?

Hmmm. I would think that good conductors usually don't make good dielectrics because, instead of storing energy by shifting polarized molecules around, most of the energy is expended moving electrons around. Insulators don't allow much current flow, so they typically make much better dielectrics than conductors.

Unfortunately that's more of a guess than anything else. I have nothing to back that up and I think we may have reached the limit of my knowledge in this area.

 

[AlphaLearner]

Hmm... surely! Will definitely go through a round and comeback here to conclude and verify.

 

[UsableThought]

Insulators don't allow much current flow, so they typically make much better dielectrics than conductors.

This was something Maxwell looked at when working up Faraday's research - I was just looking in a double biography of the two men & this particular point was mentioned in a passage where Maxwell is conceptualizing models of flux. It's over my head as to the exact meaning (I don't have the math to understand anything Maxwell did), but still interesting. From a passage on p. 160 of Faraday, Maxwell, and the Electromagnetic Field: How Two Men Revolutionized Physics, by Nancy Forbes and Basil Mahon:

In Maxwell's fluid model of the static electric field, substances like metals, in which electric currents could flow freely, took no part except that their surfaces could act as sources or sinks. Electric lines of force occurred in insulators - substances in which current did not flow. As Faraday had found, these substances varied in their ability to conduct electric lines of force - each had its own specific inductive capacity. For example, glass conducted electric lines of force more readily than wood.​

Etc.

 

[Sharad s]

The good question
The conduction of electricity through the conductor is a interesting phenomenon. Here the conductor's are those which allow the current to pass through them. ACC to chemistry the conductor's must have an single free electron in its outer most orbital thus when the energy is passed these electrons get ditached from the atom and has the negative charge over it. When these electrons come in contact with the positive charge due to change in potential of +ve & -ve particles these release the energy this is the electricity which we get. Electricity never flow from +ve to -ve due to low potential

 

[Drakkith]

ACC to chemistry the conductor's must have an single free electron in its outer most orbital thus when the energy is passed these electrons get ditached from the atom and has the negative charge over it. When these electrons come in contact with the positive charge due to change in potential of +ve & -ve particles these release the energy this is the electricity which we get.

The very best conductors happen to have a single electron in their outer shells (silver, copper, gold, and aluminum all have an electron configuration of s1), but the vast majority of conductors do not have a single outer valence electron. After aluminum, the next best metallic elemental conductor is calcium, which has an electron configuration of s2.

Also, note that the electrons are already detached from their atoms prior to any current flow. The metallic bonds that form between the atoms exist primarily because all of the atoms in the entire material are sharing their valence electrons with each other.

 

[Sharad s]

The resistivity of the material depends on all those factors it's true. The resistivity is also because of the nuclear charge acting on the free electron which is participating in the conduction of current. The increase in the temperature of the wire will provide the essential energy to the free electron to go away from the nucleus of an atom. The Next factor length and area of crossection due to the increase in the number of atoms the nuclear forces play an important role and thus the resistivity of the material increases.
If any queries contact my mail and id

 

[Drakkith]

The increase in the temperature of the wire will provide the essential energy to the free electron to go away from the nucleus of an atom.

A free electron is already free of its bond to any single atom. That's what "free" means.

 

[Sharad s]

A free electron is already free of its bond to any single atom. That's what "free" means.

The free electron mean the single electron in the orbital of the ultimate shell

 

[nasu]

No, it means that is in no specific atomic orbital, as Drakkith said. If you are more familiar with chemistry, think about a molecule. The bonding electrons are not in atomic orbitals but in molecular orbitals, which are extended over all the atoms in the molecule. The benzene molecule is an example of such de-localized electrons. A metal is like a huge molecule, with the binding "orbitals" extending over the whole metal. In metals there is no such thing as "detaching" the conduction electrons from the ionic cores. They are already as "detached" as they will be. The concentration of free electrons in metals is also independent of temperature, as they are all free at zero K.
In semiconductors you need some energy to promote electrons from the valence band to the conduction band. This energy is provided by thermal motion or/and absorption of light or maybe other processes. Maybe this is what you have in mind.