Does current really flow ?

Discussion in 'General Electronics Chat' started by MathematicianKing, Nov 12, 2017.

  1. MathematicianKing

    Thread Starter New Member

    Nov 10, 2017
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    Hi friends,

    This question may sound a bit strange, and maybe I wont put it right enough, but do you believe that there is something really flowing inside wires, i.e. the thing called current ?

    I mean, I have a feeling that electrons don't really flow inside the wire, and it's more like a wave of something that propagates, but without actual flow of anything, if you know what I mean. We have a tendency of thinking that everything is like little balls moving about, but when you get down to a micro level, I think these notions break down.

    I am not a physicist so I might be talking nonsense........ Well

    Do you believe that electrons really are like small clouds or balls moving around ? Or are electrons something else?

    In fact, is it the electric and magnetic fields that move like waves inside the wires? It could be that its just the fields that move, and not the electrons.

    This would mean the notion of current is flawed in some way? If there arent really little balls flowing, then how can current make sense?

    Isn't current just a macro construct to understand circuits?
     
  2. MrChips

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    Oct 2, 2009
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    Hey, you're not crazy. There is some truth to what you are thinking. There are no marbles moving around like we would like to imagine. It is more like a nudge. One electron creates a displacement and a wave propogates along and that is what we experience as current flow.

    Edit: Ever watched a wave in the spectator stands at a ballgame?
    The fans don't change seats. Yet we observe a wave propagating around the stadium.
     
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  3. be80be

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    Jul 5, 2008
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    Kind of deep it's like saying a transistor is a amp well yes it is but really that's because it was said to be and defined that way current moves you can see it jump a gap.
    So great minds of the past tested these ideals and the math holds up, How much it moves the way it moves
    you could talk for years. But does it move the light comes on from heat of it moving a motor turns.

    Take it like this if you open a wire nothing moves you put a light bulb in there and close the circuit add a voltage to cause movement you get light.

    So something moved.
    I don't think wave would hold up because if you look at wave it moves easy.
    I'm sure they said the same thing and watched it jump a gap.
    Light went on in there head and said ok lets make some more battery's and force it to jump the gap.
    So they took notes and watched and said what could cause this.

    Well this could happen when you push something threw a small hole it makes heat, The wire your moving current makes heat.
    So it's making heat so something is moving and it's not easy to move because it's making heat.

    I would go with the idea it's moving. I would say that's what they did to.
     
  4. nsaspook

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    Aug 27, 2009
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    Sure current flows very slowly with very little energy in most circuits as fields also move around conductors much faster while transporting the usable energy of the circuit. It's a system that needs both to function in current electricity. What's flawed is the idea that electrons (or any charge carrier) carry the energy of a regular electronic circuit like water in a hose. That's just a poor analogy.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    Yes, electrons do flow in wire and there are instruments that can detect the charge of an individual electron as it moves in a circuit.
    It's also possible to detect the difference in voltage of one electron on a very small capacitor.

    If electrons didn't move, how would you explain the change in voltage as a capacitor charges?
     
  6. Kjeldgaard

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    Apr 7, 2016
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    I was aware that the electron velocity in a wire was relatively low. But I was surprised by what a search led me to the Wikipedia article on Drift velocity which, in addition to a lot of formulas, tells the following about a copper wire:
    "Therefore in this wire the electrons are flowing at the rate of 23 µm/s. At 60 Hz alternating current, this means that within half a cycle the electrons drift less than 0.2 μm. In other words, electrons flowing across the contact point in a switch will never actually leave the switch."
     
  7. MrAl

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    Jun 17, 2014
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    Hi,

    I have read that the velocity of electrons is less then the speed of light, but because they bounce around in different directions their average propagation from one end of the wire to the other is much slower and yes is referred to as the drift velocity. That is in normal conductors not super conductors. In low temperature super conductors they form pairs which can drift though the medium much easier because they somehow become synced to the material structure like sound. In high temperature super conductors they drift only partly like that.

    Most of the stuff we do in electronics though relies not on the micro structure of the process but on a statistical view where we look at average behavior of many electrons and draw conclusions that work in everyday life. That's actually how we deal with everyday life anyway even for stuff we see and feel every day, day after day, without realizing it, and that is what we call common experience. Individual electrons or for that matter individual sub atomic particles of any kind are not in our every day experience so we find them harder to deal with.
     
  8. nsaspook

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    https://www.google.com/url?sa=t&sou...ZALUQFggmMAA&usg=AOvVaw32-osI7Ogw5GRMue1G-tAS

    Electrons that left Oregon in 1970 will take until 2912 to reach southern California on a HVDC power line. Current is like the links on a bicycle chain. They move and carry power due to the tension on the chain in a circuit. The links, chain and gears form a tension power transmission system that like an electrical power transmission must be seen in unison to correctly understand energy flow.
     
    Last edited: Nov 13, 2017 at 6:31 AM
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  9. BR-549

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    Sep 22, 2013
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    Yes it flows......but in a way that you have never seen or thought of before.

    Charge is self repulsive. Water is not. Air is not. This is why it's hard to explain charge flow.

    On a conductor.....there is a thin electron film on the surface. This film is always there. This film is always flowing.

    This film never goes anywhere.......it sits there and all the charge are constantly repelling to one another. They are in constant collision with each other.

    If you could see them.....they are colliding and moving in EVERY direction. When we put a voltage across the conductor......ONLY a portion of them will move down the conductor. For every electron that leaves the conductor.....another electron has to be added. The film is always there.

    The portion of charge that flows down the wire is called current......but there is still a lot that are colliding sideways......and don't flow down the wire. A lot of the film is not current.

    You can increase the voltage and it will take a larger portion of the film. You will reach a voltage where all the film will move...and the wire will be very warm. If you increase the voltage farther.....you will pull non free electrons from the conductor....and it will start to melt and glow.

    The speed of all the electrons......whether it's the current or film.............is faster than anything that you have ever worked with. Much, much faster than a bullet. BUT...BUT.....the distance it can go.....before colliding with another electron.....is very, very short.

    Current is the result of billions and billions of small colliding currents. It's a collective average. If you put a plane across a conductor......and watch every electron the makes up an amp.........each electron that passes the plane will have a different speed and a different direction(or angle) coming across that plane.

    Does any of this make any sense to you?
     
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  10. philba

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    Aug 17, 2017
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    Hopefully we've got whether electrons flow or not sorted now. Here's one to add to the misery. Electrons flow from negative to positive. An electron has a negative charge and is attracted to an atom that is missing an electron which has a positive charge.

    I thought the film effect was only in higher frequency AC.

    As long as we are talking AC, don't the electrons stay in approximately the same spot, being push back and forth.
     
  11. MrAl

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    Jun 17, 2014
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    Hi,

    I think you mean skin effect. Yes that's for AC.

    The electrons drift back and forth too with AC.
     
  12. wayneh

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    Sep 9, 2010
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    Yes, I 'believe' electrons flow, which is to say I believe the science that has led to that conclusion.

    The thing that confuses folks is that while an electric field moves through a conductor at essentially the speed of light, the current of actual electrons responding to that field move fairly slowly as described already in this thread.

    I disagree with @nsaspook that water flow is a poor analogy for this. I think it holds fairly well. Suppose there's a 4-foot diameter, ten-mile-long water pipe between your city's water tower and your faucet. The pressure (like the voltage field) supplied by the city appears at your faucet almost immediately. But if you open your faucet, the water leaving the tower today won't come out of your faucet for days or weeks. The water you get in your sink left the tower a long time ago. With all the details of pipe dimensions and faucet flow rate, you could even calculate the nominal transit time. Same deal with electrons - you could calculate an estimate of the electron flow rate required to light your light bulb. The one big difference is that a conductor is always already "full" of the flowing fluid. You don't need to fill the pipe first. Thank goodness! We'd all be sitting around waiting for the wires to fill up with electrons.
     
  13. Lumenosity

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    Mar 1, 2017
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    Awesome thread !!!
     
  14. nsaspook

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    The main problem with that is you're using an open loop analogy where the equivalent to current never returns to the source like it should in a closed-loop system (most people have no idea about the details of electrical systems also have no idea of the complexity of closed loop systems). Even the closed-loop water analogy misleads as the energy of a circuit does not follow the circular flow of current, it travels from the source to load on all paths in circuits which is why see source to load power flow with AC current.

    It's very logical to think in that analogy that the energy of the system is transported via current (IT IS NOT because charge 'electric current' flow is not energy flow) if we see water draining away as the equivalent.

    There is a better way.
    http://www.abc.net.au/science/articles/2014/02/05/3937083.htm

    If you want to improve STEM education then stop with the poor analogies when we teach basic electrical concepts.
     
    Last edited: Nov 13, 2017 at 4:18 PM
  15. BR-549

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    Sep 22, 2013
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    I don't recall the TS asking about power. I think he wanted to know if there was actually anything physically flowing in a circuit?

    I didn't take that to mean power.
     
  16. wayneh

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    There are two problems with that approach. The chief problem is that even many college-level physics students cannot readily compute that miles per hour, times hours, gives you miles. In other words they need a very simple touchstone analogy to give them any chance of understanding voltage, current and resistance at the level of ohms law. A few bright students don't need the water analogy and would be better off not muddying their thoughts with it, but the rest might have something to recall years later if they can relate electricity concepts to something more familiar.

    The other problem with starting with the field explanation - laudable because you can stick with it to any level of detail - is that you end up explaining things with ... a field. When someone can explain why a magnet works, maybe that will be OK but in the meanwhile we all have a far better intuition for gravity than for magnetism. We don't know why gravity works either, but we can relate to the waterfall and the fact that the water has energy because of the gravity field.

    I guess it comes down to using the right teaching tool depending on the student. EE and physics students shouldn't talk about water. But try explaining electrical concepts to your grandmother or your neighbor, assuming neither is especially bright. Talking about fields will get you nothing more than a glassy-eyed stare.
     
  17. nsaspook

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    Sorry (not aimed at you personally but in general), IMO lame excuses that leave us behind in a world that needs more real science, not less.

    I would say that intuition for electricity is foolish if the concept is brain-dead after simple battery and lamp DC circuits. There is no need to change the teaching of voltage, current and resistance at the level of ohms law. What's added is just a little of the microscopic scale of ohms law with a basic intro to fields similar to that link for basic electricity and electronics. When I was in my HS electronics class the EE teachers from TI didn't waste time with water analogies. They were teaching the next generation of possible future EE and physic students.

    We are explaining things to possible future EE and physic students so lets treat them to a consistent and correct path to that possible future.
     
    Last edited: Nov 13, 2017 at 7:55 PM
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  18. MrChips

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    And then to add further confusion, toss in the wave-particle duality of the electron.
     
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  19. nsaspook

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    Exactly, another reason to move to a more fields (as physical objects that transfer energy) based approach to basic electronics because even with that rabbit-hole in the mix its still compatible from a lamp with a battery to the QM of electron tunneling. Personally I think students would GROK the idea of energy via fields as material objects much quicker today because of all the Sci-Fi storytelling that uses them in various ways.
     
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  20. DonLduk

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    Jun 12, 2017
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    Actually, I remember from university that electrons flow in the opposite way. I barely remember, but it has something to do with displacement: current happens when a "hole" is left by the electron and it is filled back.

    A quick googled to this theory and I found this:

    https://www.quora.com/Why-is-the-di...-to-the-direction-of-flow-of-electric-current

    "
    Current electricity was discovered in the 18th century, and investigated by a number of people. They needed a direction to attribute to that current. They had nothing to go on (since the electron was not discovered until 1897). So, in the end, they had to make an arbitrary choice, and decided to label one pole of the battery as + and the other as -, and to define that electric current flows from + to - (with the electric field pointing in the same direction, thereby causing the flow).

    Unfortunately, when the electron was discovered, people suddenly realised that the earlier arbitrary choice had been wrong. But it was too late. So we are saddled with the same + and - poles of our batteries, with the negatively charged charge-carriers flowing from - to +."
    "
     
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