What Are Electrons REALLY Doing In A Wire? Quantum Physics and High School Myths
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- čas přidán 3. 02. 2020
- In this video we explore the surprisingly complex and quantum mechanical physics of an everyday situation: electrical current flowing in a metal wire
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Never heard of pinball analogy taught before
Neither did I
Always learning
Wow, finally a good physics video that gets the balance between layman simplification and real physics right. Excellent work!
Sure, except soon Quantum physics get involved all lecture could be as well in Japanese 🤣
Love the Kelvin's absolute zero score on the pinball :)
Wow... a physics video that doesn't suck. Bravo.
After every video I feel like I need to relearn physics all over again and it took me a really long time to learn textbook physics. I want to cry.
This is a really clear way to explain it thanks for the video!
I would love for you to make a video and break down what exactly you learned from this? Maybe re-watch and pay attention to the screen so you can see you didn't learn anything at all. You fool!
In grad school, I learned the Drude model and how it gives qualitatively good results for some predictions but misses the mark on others completely (like the temperature dependence on conductivity, as you mentioned). We ditched it early and went into the semi-classical model, but dove in starting with the math. I came out knowing how to do Bloch's theorem and everything else, but didn't take away the right qualitative picture. This explanation was incredibly well done and appropriate for laypeople _and_ experts. Awesome work
Super underrated channel! Glad to have found it and subscribed!
I've been studying physics for a long time and have been teaching physics for over ten years, and I've never seen the pinball machine analogy before.
I wish this exploration could be extended slightly more to describe what the electrons are REALLY doing in wires at different steady-state voltages (in a circuit), and especially when a step change in voltage propagates along a wire or circuit board trace. Intuition from fluid or gas flow would suggest they are squeezed in closer together at higher voltages... or at least exert more force on their neighbors even if maintaining the same (average) distances. This all relates to it taking a small but finite time for a change of voltage across the circuit to be felt throughout the circuit... and that propagation must correspond to something interesting happening at the electrons-and-atoms scale.
If charge field is outside the wire then gas theory does not work as electrons don’t really travel just the charge field, the best part of your question is what happens at atomic and subatomic levels, electron tunneling vs field “tunneling”?
This excellent video is about the flux of charge. The flux of charge however is not conserved as the video more or less implies. Take the divergence of the Maxwell-Ampere law and you will see that the divergence of J (the flux of charge) is not zero when the electric field is changing with time. These issues are explored in some papers that might interest you. I suggest that it is necessary to use the entire right hand side (source term) of the Maxwell-Ampere law as a definition of (total) current when electric fields vary in time. The total current is conserved perfectly, whenever the Maxwell equations themselves are valid. See arxiv.org/abs/1805.04814 ; arxiv.org/abs/1905.13574 . When current is confined to circuits, Kirchhoff's law emerges for total current. In some cases, Kirchhoff's law is nearly exact, see arxiv.org/abs/2002.09012 but in other cases, extra conditions have to be added to deal with radiation from the circuit, the skin effect, and so on. I add for those less familiar with these issues that electric field change very rapidly with time in the circuits of our computers, volts in nanoseconds (0.000000001 seconds).
The electric field adds to the potential diagram where he shows the ionic cores and bands. This results in a slight downward slope to the entire potential curve...and the electrons kind of move in response...like a kid sliding down a playgroimd slide...it's a little more complicated than that because electrons can't occupy the same state at the same time, so you end up with what's called a Fermi sphere of momentum states, almost all of them cancel except for a few near the Fermi energy...those are the ones contributing to the net current in the wire. The higher the voltage, the greater this slope and the more electrons are excited up to the states near the Fermi energy...so more net current.
Electrons don't move.. maybe 🤔
@@thomasauslander3757 I think they do, just not the way most people imagine them "moving". When talking about a collective wave function, the whole idea of an individual part of it moving is a strange thing...it's more like the probability has changed..but that change happens in a certain way that is heavily influenced by the ion core arrangement. The result has implications that contradict the old models of conduction and those models are still popularly used.
That was interesting, but you didn't really cover how an electric current transfers energy through the wire under a voltage differential.
I would LOVE an explanation of that with this model.
I really like how you don't back off from the accuracy in your explanation and water it down. The Bloch state, Phonons. Honestly I didn't have much hope when I randomly came across this video but you sure did answer the question very well. Well done
Wow what timing! I just read about Bloch's theorem last night for my quantum II reading. Good video; it's nice to see misconceptions cleared up. Bravo :)
This was very, very informative. It cleared up a lot of confusion about quantum physics. Thank you so much for this!
This is not only in the wires. This explanation underpins all the solid-state physics, including the working of transistors.
Thank you for the video, you did a great job of explaining the current in a wire...
This makes the electron "cloud" seem so much more intuitive.
Subscribed! I've taught these concepts to my HS Physics 2 students using various media, including PhET's multiple atoms applet. I'd recommend that as an interactive to go along with this excellent video. Really nice job!
Thanks! I'm familiar with the PhET applet's they're really great and it sounds like you're taking a really good approach. When teaching something like this you can start with a single coulomb well (i.e. "a single atom") and then add more wells one by one in a row until you see the bands start to form. It's really helps build intuition.
For some reason this was recommended to me and before I saw the views I thought it would've had like at least 500k nice video though :)
Thanks!
I am more and more amazed at how many channels with serious quality do not have many subs. This is a perfect example.
Great Job! Nice to see your video doing well as they should.
I wish I could like this video 100 times over. I love that your explanations kept referencing the higher level spatial/geometric/network visuals
This was a good video. For some reason it made the concept of a phonon incredibly clear.
I've had an incomplete understanding of band gaps ever since high school. Thanks for the diagrams and explanation.
Glad to help!
It's (band) gap in your knowledge
@@atomsandsporks6760
Hijacking thread for at-mention...
Re: lattice wave vs electron wave, I wonder if the following analogy has any uses?:
A wave pool is filled with water but the surface is packed with a layer or three of beach balls. If you push the ball nearest to you, that energy will propagate out through the other beach balls as a somewhat elastic wave. But there's also the underlying wave of the water substrate that will also influence the movement of the balls.
What a great video! Suggestion: If the original script was much longer and you cut pieces to create a more appealing version, do release longer versions based on your full research on some other channel. They need not be as polished but would sure love to hear more. Also, include the names of books you referred to in the description! Thanks! :)
Great explanation, nice balance of accuracy and clarity. Subscribed
Very well done video. Looking forward to more!
Cool video, thanks. I'm one step closer to reconciling my understanding of chemistry with my understanding of physics. In chem, we have the concept of electron shells -- the s-shell, p-shell and so on -- with the electrons in each shell being at different energy levels, and with a gap between shells where electrons never exist. We also know the shapes of those shells, from which it's obvious that electrons are much more like waves than particles. The idea of a much larger bandgap forming among clumps of atoms isn't something I recall in chem, but the idea that groups of atoms together can support the formation of even more distant shells that sort of merge together definitely has an intuitive appeal to it. What's still not clear to me, though, is how electrons (waves) move or otherwise behave to create electricity. The "high school" explanation is that electrons flow -- coulombs per second and all that. But "flowing" in a classical sense has never made sense to me.
As I understand it, the energy (electricity) is not carried by the electron flow itself, but by the electromagnetic field generated by the electrons. This can be represented by the Poynting vector.
Nice!
Gonna watch this when I get home! real excited!
This is brilliant! Great explanation!
The best video I've seen on this topic. Thank you!
This is an awesome video! Looked as professional as those channels with millions of subscribers and taught me something new!
Great to hear!
Deadly video, head a bit sore from getting around the concepts but great detail. Thanks
Excellent video! I don't know why you don't have more subscribers I know so many people who would enjoy this content a lot.
Hard stuffs made pretty simple! Great video, and the "most correct" I found on youtube: others are always talking about electrons scattering on the atoms, that is a sure simplification, but leads to misconceptions.
Awesome guys thanks for explaining in simple words
Im scared. You either dumbed it down so much that i was capable to understand Quantam Physics or I am a natural Quantum Physicist. Basically i understood felt and visualaised everything you said,
Read into quantum physics
No one has explained this better than you. I struggled with energy bands in electronics. Wish I had seen this.
Real enlightenment on the nuance of the subject. Thanks a lot.
... from India
Very good so did subscribe. I love these kinds of videos and you've done a fantastic job.
Quick question when it comes to temperature varying resistance. Is it possible for a difference of 30 or 40 degrees Celsius to affect the transmission of broadband internet signals? Does colder months mean the the resistance of the copper wire is less therefore the speeds will be more? Is it possible to measure the decrease of resistance in copper over 1km if the temperature is 30 degrees less or does the temperature need to be significantly reduced to notice a change?
Wonderful video... Just wonderful!
You know it's gonna be a great day when a new video of Atoms and Sporks shows up in your recommendations😊
Thanks! Glad you enjoy them.
Wow! 👏 your explanation is great.
Loved it! Could you do one on the spin of the electron and how these degrees of freedom can be used to carry information aka spintronics? Thanks
Grate video! Sending this to all my students!
bro this channel is criminally underrated!
This channel deserves more publicity. I predict 100k subbs in a year or two.
P.S. if you make your explanations even more easily understandable for people who do not study physics, you'll have a VASTLY greater target audience. Barrier to entry here is quite high, as a high-schooler would not understand this very well... I recommend you study exactly how other big science channels make their high level content still somewhat graspable by the average enthusiast. Good luck!
Thanks! I very much appreciate the feedback, here's hoping! As for the content, we'll see on that too. I am definitely trying to grab the enthusiast, but not really trying to replicate the big science channels. I guess, in a sense I started this to *not* be like them. There's a million channels churning out the same, often wrong, explanation of Schrodinger's Cat or Heisenberg's Uncertainty, often just copying each other, but I really don't feel like there's many (or any) looking at that real applied physicists actually do.
@@atomsandsporks6760 Try scoring a collab...
Very good explanation that's much more consistent with the 19th century classical electromagnetic theory, aka Poynting Vector.
Brilliant - well done!
Great video and animation 🙂 I recently learned about electron drift velocity but what I have seen seems to explain it in the old model. Can you explain it in the updated mode you used?
An electrical current has units of "charge per second" which passes through some cross-section. So if you have an electrical current there must be a motion of charge. The dubious notion of "drift velocity" comes from basically starting from that basic truth and trying to divide a current by an estimate of "number of charged particles" to get a velocity. When you do that you will find a very, very slow velocity and it is sometimes said that that is "the average progress our pinballs make". That's... okay... it is in some sense true. But it's important to know that no actual thing in the system is traveling at that speed, it's a "net rate of progress of charge", nothing more.
@@atomsandsporks6760 you are incorrect. This is a rate of induction.
Finally some clarity. So many teachings lead to dead ends. It seems more elegantly simple to think of electric charge fields and their aggregate accumulation. An important milestone for me was integrating the elastic and repulsive nature of electron electron interactions. Now if I could just sort out electron spin............? Perhaps spin is a quality (of tumble induced by curved path) and counter to the electrons field disturbances of the spin opposed electron in same orbital space. Perhaps If they didn’t tune to align that way they would bounce out of the orbital.?
Very good work.
The explanation covers everything , and the visualization is very great, one of the best physics videos keep on 💪
Excellent video!
like charges repel, so electrons just repel or "push" each other from negative terminal of the battery to positive terminal. the difference in energy between positive and negative terminal is called voltage.
Someone on an audio website insists that the electrical current in a power cord permanently affects, changes, undergoes some sort of molecular rearrangement of the dielectric material around it with its interaction with it and refers to it as "burn-in". I could understand that different insulating materials can affect the current through the wire but make permanent changes in the wire?
I’m gonna get “particles aren’t little billiard balls but rather wavey things that do regular wave stuff” tattooed
Very nice. Thank you.
Terrific video (thanks!). On the matter of what makes a medium transparent, ie) photons not having enough energy to be absorbed, I was taught that photons are in fact absorbed and then remitted by the nucleus in the same direction. How do I reconcile this?
To be clear, there are absolutely no electronic transitions involved in the transmission of light through a material. So it is incorrect to say that electrons are absorbing and re-emitting. That's a very clear physical process and it's not occurring. HOWEVER, there is a way of deriving the transmission of light in terms of so-called "parametric scattering processes" where a parametric scattering event is one that ISN'T associated with any sort of internal change in the atom (i.e. it's not a true transition, but rather a "zero energy" scattering event). An example of such processes is Rayleigh scattering. There's a good educational video at Fermilab's CZcams which discusses this approach to things. But again, no electrons are being harmed/excited in such a picture. It's largely a way of rebranding the centuries old Huygen's Principle
That brief explanation would make a great video the way you made this one. I don’t remember seeing or hearing anyone explain such complicated material (or waves?😁) as well as you did! I’m an old, low level physics “hobbiest” , so I’m amazed that I could watch this video, and even understand (most) of it. Thanks and I’ll be watching every vid you make!
Fun fact this is all theoretical. Atomic theory specifically. No one has proven what an atom even is.
fun fact: it's proven as closely as there even can be something like a proof in science. proofs are a thing in maths, logic and some branches of philosophy. not in physics.
George Box: "All models are wrong - but some are useful". nicely done.
Good video, but I felt that it was missing treatment of how the semi-quantum picture fixes the issues with the pinball intuition you outlined (eg the relationship between electrical conductivity and temperature at 3:40). Could you clarify how it does so?
tl;dr: In a semi-classical model you keep the pinball idea but the number of balls are different, the number of bumpers are different and the rules for what happens when a ball hits a ball or a ball hits a bumper are different and solved within quantum mechanics itself.
When you do this you'll get the correct trends both qualitatively and quantitatively.
To be more specific, for one, the semi-classical model changes the number of things that can scatter - specifically, it's not related to the number of atoms but rather related to the number of electrons *that have energies near the edge of the conduction band* which is only a tiny temperature-dependent fraction of all electrons and the average intensity of lattice waves, which also is not simply related to the number of atoms. Second the physics of scattering of these objects (delocalized electrons and lattice waves/phonons) are very, very different than free electrons vs. free atoms. Because of this, under the hood, scattering (i.e. how energy and momentum is traded between electrons and between electrons and lattice waves/phonons) is handled entirely quantum mechanically in a semi-classical model.
So a semi-classical model is like a pinball machines where certain truths of the deeper quantum pictures are stapled, somewhat inelegantly, to key places because they are essential.
I believe the video is the semi-quantum picture. I imagine a full quantum picture would require QFT (the latest and most up-to-date quantum theory).
If a metal is more dense, it also contains more electrons, so that should even things out. Yes, there are more things to bump into, but there are also more of the things doing the bumping.
Really Excellent !!!!!!
its funny how didactic you get, though you give a pretty correct picture, even talking of tight binding. I like it XD
I have a question if I may: How do I calculate how thick a cable should be when making an electromagnet?
I gonna assume that the score in pinball machine is temp in Celsius. Cool 😎
Did not really think of it but you are right is absolute 0 K in Celsius -273.15.
quality content. came from reddit you are doing good job, please jump into some advance topics as well. thankyou for this
I think different metals are more conductive because the amount of electrons "orbiting" in their valence shell. Not the density of their nucleus in the structure.
Brilliant explanations
Thanks!
Question. Doesn't the image around 9:52 show the conduction band of electrons too low in the potential energy well of each atom? In other words, if they were free to move between atoms wouldn't their energy be more in the yellow orange region? The white band looks trapped by the potential peaks between atoms.
Great question, you're definitely right that the "most delocalized" states are going to be between the yellow/orange region and the top of the potentials. Though in reality when we talk about a given material those states may not always be the band we call the "conduction band". I'd encourage to you play with this little applet:
www.falstad.com/qm1dcrystal/
This applet solves the math of quantum mechanics for the electron states in a certain repeating potential. You should select "Coulomb-like" from the pull-down menu as this will be the most like the true electrical potential of an atom. You can then click on the light grey bands that show up and it should show you what the electron state looks like below. You should see three band, with the top most being the most delocalized and very broad and the bottom one being very deep in the Coulomb potential and very thin and very localized. You'll notice that this will show even the localized ones as "repeating", in reality a given electron can be in a superposition of these states and thus can be in one where it's really just trapped in one peak (i.e. associated with a specific atom).
Man this was the best explanation!
Very nice. Thanks
Ah.Lattice waves explains why things that tend to be thermally conductive are also electrically conductive, or vice versa. Materials that can equalize thermal inequalities faster and have less of a gradient probably conduct electricity more efficiently due to less scattering.
Extremely informative
Thank you 😊
Glad it was helpful!
Kindly let me know which books to read so that I can have a clear understanding of these, and not the classical way things are taught as most places and courses.
I just wanted to know about current I didn't understand a thing
Current(I) is the electro magnetic field flow of charge, in this case mainly due to the emf on the surface of the copper wire circuit.
Mr. Derek, come here and learn something useful for a change 😂
BTW the way you explained the valent and conductive zones is mind-blowing. Great stuff !
im real upset that i didnt get to learn this in high school. but at least im making up for lost time so thank you so much for making this video
Space has special lanes for photons, electrons, and other fluid particle waves. Vacuum of free space for photons. The conduction band for electron.
great video!
Hey! Just FYI I find your videos fill such a perfect niche on CZcams and I learn so much from them. If you had a patreon or anything like that id be happy to support! Thanks again all your vids are great
Thanks! No Patreon at the moment, just trying to build a viewership for now.
I had to rewatch 7:05 moment like 4 times. At 7:40 it got quite hard to follow so until the end I didnt get much. Anyways I appreciate the effort put into this video!
I was taught that free electrons just kind of shifted from outer shell to outer shell (because the outer shell bonding is so loose. And that the atoms with high electron count are best conductors). Now there is this theory that the electrons do not travel at all but instead wiggle or "excite" in place generating an EM wave. This EM wave is the energy that travels and cause electrical energy. But what about the battery where the electrons are indeed or presumed to be pulled to one pole???? How does the whole scheme work??
I think your term "delocalization" term confuses more. Does it mean the electron has moved?
I found the video confusing.
Great video sir
Thanks!
Very nice.
I like this explanation, it also explains how if you reduce the lattice waves enough that they no longer obstruct the electron, you get a superconductor.
At 1:45, wires are VERY nearly equipotentials; due to the high conductivity of metals, very large currents can flow to neutralize any potential differences.
Thank you! So, in a Blach state, each electron is a wave. Do they have different frequencies, amplitudes, or signatures? If so, does it make an observable difference?
Also, does a current have anything like a frequency? Even if there's a big variation between the individual electrons, it seems like there would be a mean frequency, right?
I'm not talking about the frequency of alternation in an AC current, by the way, but the quantum wave phenomenon. Thanks!
Yes, Bloch states have something called a "crystal momentum" and a "band" (we learned about what bands are in the video) associated with them. This makes them different from one another. Crystal momentum is approximately the wavelength of the electron wave. Being a bit more careful, (unfortunately there's a lot of subtlety to this that I'm trying to avoid) the crystal momentum is the amount of momentum an electron in a solid would have if the atomic lattice suddenly disappeared and it turned into a free electron.
As for average frequency there is an average energy of an electron in a material. It ends up being about 3/5ths of the so-called Fermi energy. Probably not worth talking about where the 3/5ths is coming from (calculus!) but the Fermi energy is something you can look up for a given material. You'll find tables and such, especially for metals. It's also related to the "electron affinity" or "work function" of a material so if you can find a table of that you can convert it to the Fermi energy.
bloch elecrons with near fermi energy already formed the stationary waves that feel nothing of other stoms, they can move fast
Thanks for the video. 👍
Very clear. Now I see the inpact of quantum mechanics on our everyday life. And I understand why I get shaken up so hard when I stick my fingers into a plug: it's just all about waves! Just kidding. Wow, the complexity of the situation is mind boggling.
Amazing video
So, the wire "shakes" as electrons are waving thru, and this mechanical movement of core atoms make heat, right?
I am trying to figure out how electrons move through car. I know electrons move from the negative to the positive in a battery and I am trying to reconcile how is it that the whole chassis of the car works as a wire that directs the force precisely to the components.
Nodes, anti-nodes valence and conductivity.. thanks 👍
THIS VIDEO IS AMAZING!!!!!!
thank you, here from the veritasium video about electricity... the reality is that we're probably dealing with some spooky action at a distance where the information traveling across the wire is actually traveling faster than the speed of light.
Actually, the speed of electrical force spread out in wires is slightly less then that of light in empty space. Like, down to 50% in some cases.
That guy has no clue!
The electron is so light and moves so slowly it does not seem to possess enough KE to transport the electrical energy. Can you help?
As to your last statement: I did and I did. This was a very clear explanation of a murky subject.
Wait do electrons accelerate as they advance down the wire? How come current (I) retains the same value along the circuit then? (or is that just in theory and in reality it would be slightly higher near the positive end? I mean objects have greater velocity as they get closer to the ground. I've never thought about electrons this way, please help lol.)
how free flowing electron affect the stable atom? Thanks
Could you please enable subtitles? It would be great :) Thanks