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I How does electric current flow through a conductor

  1. May 21, 2017 #1
    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, wont the atoms in conductor turn unstable leading it to disintegration/collapsing of conductor itself?
     
  2. jcsd
  3. May 21, 2017 #2
    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, wont 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 - 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.
     
    Last edited: May 21, 2017
  4. May 21, 2017 #3

    Drakkith

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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.
     
  5. May 21, 2017 #4
    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.
     
    Last edited: May 21, 2017
  6. May 21, 2017 #5
    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.
     
  7. May 21, 2017 #6
    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?
     
  8. May 21, 2017 #7
    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.
     
  9. May 21, 2017 #8
    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...
     
  10. May 21, 2017 #9

    Drakkith

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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.
     
  11. May 21, 2017 #10
    Done, Thanks for help. Now the thread can be closed.
     
  12. May 21, 2017 #11

    Drakkith

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    Why would we close the thread?
     
  13. May 21, 2017 #12
    My doubts for now have been clarified.
     
  14. May 21, 2017 #13

    Drakkith

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    Others may have questions though, so the thread will stay open for them. :biggrin:
     
  15. May 21, 2017 #14
    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.
     
  16. May 21, 2017 #15
    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 cant 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)
     
  17. May 21, 2017 #16

    Drakkith

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    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
     
  18. May 21, 2017 #17
    Another instance of conduction via plasma is . . . lightning! From the Wikipedia article on lightning:
    Etc. etc. More generally, Wikipedia's article on plasma states:
    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:
     
  19. May 21, 2017 #18

    Drakkith

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    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
     
  20. May 21, 2017 #19
    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?
     
  21. May 21, 2017 #20

    Drakkith

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    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.
     
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