But good sir, what is electricity?
68 comments
·February 23, 2025movpasd
tzs
It probably should be noted that the reason the drift velocity is so much lower than velocity due to thermal motion is that electrons cannot move very far before they collide with an atom which changes their direction.
The mean distance they move in a copper wire between collisions is about 0.00000004 meters. At 100 km/s it would take 0.4 picoseconds to travel that distance.
pkoird
Just to clarify, the high speed at which electrons generally move around in metal is called "Fermi velocity". Like you said, since it's random, on average it cancels out to 0. When applying an electric field, the electrons achieve a non-zero average velocity which is called the "drift velocity".
sfn42
Is this related to how some materials become superconductors at low temperature? Does the slowing down of this electron flux improve the material's ability to conduct electricity or is there some other mechanism at play?
khold_stare
Superconductivity is fascinating. I don't know how people were able to come up with the explanations. Crudely, the reduced temperature means less jiggling of the metal lattice. This in turn makes it possible for the nuclei to be pushed around by electrons to form essentially sound waves (phonons) in the lattice (think of the lattice compressing and expanding due to interplay with electrons). At a certain temperature and therefore a certain frequency of lattice oscillation, electrons pair up to form "Cooper pairs" - they move in concert due to the lattice movement. What's crazy is that cooper pairs become a sort of pseudoparticle, and their quantum behaviour is different to regular electrons. Cooper pairs have integer spin (as opposed to half-integer spin), so they no longer obey the Pauli exclusion principle and all the electrons in the entire material basically form one giant condensate that extends through the whole material and can all occupy the same lowest energy quantum state.
jaybrendansmith
That is the BEST explanation of superconductivity I have ever heard.
movpasd
Electrons are actually delocalised in a metal: rather than point particles bouncing around the nuclei like a pinball, they're more like waves that ripple and diffract around them. This means that to good approximation, the electrons pass right through each other. Because of this, I don't expect the electron motion to affect resistance much.
What definitely affects resistance is the vibration of the nuclei lattice, in which thermal energy is also stored. This vibration makes the electrons more likely to scatter. This means even in a non-superconducting metal, resistivity drops as you get colder.
The special thing about superconductors is that there's a temperature where the resistivity suddenly drops to zero. (If you look up "superconductivity resistance against temperature", you'll see some graphs showing what I mean.)
I don't know exactly the details of why this happens, but it has something to do with Cooper pairs. Electrons in these states are also sensitive to being knocked out and bumped up to regular conducting states by thermal noise.
Nimitz14
This feels like a very nice intuition to have thank you for explaining!
alabastervlog
On a whim, I bought a book called There Are No Electrons at a used book store, some years ago.
The idea of the book is that we spend lots of time teaching students various incorrect and inconsistent models for how electricity works, that also don’t optimally build intuition for working with the stuff.
The book’s remedy is to say “forget all that: here’s a wrong model that is good at building intuition for working with electricity, and if you’re not planning to go for a physics PhD, that’s much better for you than the other wrong models”
I don’t know enough about electricity to evaluate whether this was a good idea or well executed, but it’s an interesting approach.
https://goodreads.com/book/show/304551.There_Are_No_Electron...
erehweb
There is a story of a student taking an oral exam at Oxford or Cambridge many many years ago.
Examiner: "What is electricity?"
Student: "Oh, I do know, I mean I used to know, but now I've forgotten."
Examiner: "How very unfortunate. In the whole of history only two people have known what electricity is - the Creator and yourself. And now one of the two has forgotten."
ok_dad
My favorite thing about electrical theory is that all this business about flow of energy going from + to - is the idea of "electron holes" flowing, instead of the actual electrons! Basically all of electronics and electricity uses hole flow convention. It seems weird to me we don't use electron-flow convention (aka: reality), but then again I'm a weird guy.
card_zero
The terms are due to Ben Franklin:
We say B is electrised positively; A negatively: or rather B is electrised plus and A minus ... These terms we may use until your philosophers give us better.
Here A and B are Franklin's buddies, standing on insulating plates while one of them rubs a glass tube with a piece of, if I remember rightly (can't find the proper source), "buckskin". Then they reach out to join hands and a spark crosses the gap.
Problem is, it isn't even clear from the experiment which of A and B really was negatively charged, because it turns out the charge depends on the nature of the "buckskin" (or whatever term he used), and how hairy, furry, or possibly even leathery it was. The resulting charge could be positive or negative, depending. So he defined the terms, but didn't even clearly assign them to direction of electron flow.
Edit: the ambiguity is shown in this picture:
https://en.wikipedia.org/wiki/Triboelectric_effect#/media/Fi...
Here leather is above glass, and fur is below it. He was definitely rubbing glass with something like leather or fur, but the resulting charge depends on where in the series that thing was relative to glass.
robocat
> but the resulting charge depends on where in the series that thing was relative to glass
You'd think we would understand the science of contact/static/tribo electricity by now... And yet this posted 1 day ago: "Static electricity depends on materials' contact history" https://phys.org/news/2025-02-static-electricity-materials-c...
Historically, several studies have suggested that insulators could be ordered based on the sign of charge they exchange, from the most positive to the most negative. For instance, if glass charges positively to ceramic and ceramic does the same to wood, then glass (usually) charges positively to wood. Thus, glass, ceramic, and wood would form a so-called "triboelectric series."
The problem with these triboelectric series, according to Waitukaitis, is that different researchers get different orderings, and sometimes even the same researcher does not get the same order twice when they redo their own experiment.
And https://en.wikipedia.org/wiki/Triboelectric_effect#Explanati...
There are many cases where there are triangles: material A is positive when rubbed against B, B is positive when rubbed against C, and C is positive when rubbed against A, an issue mentioned by Shaw in 1914.[29] This cannot be explained by a linear series; cyclic series are inconsistent with the empirical triboelectric series.[75] Furthermore, there are many cases where charging occurs with contacts between two pieces of the same material.[76][77][47]card_zero
Woah. Well that just adds to my confusion!
praptak
I remember reading an early book on the topic where the author describes two kinds of electricity: "glass-electricity" and "resin-electricity". The experiments seemed to involve rubbing either glass or hardened resin (amber?) with something. The author (it wasn't Franklin) concluded, after a series of experiments, that this produces two different "kinds" of electricity which seem to cancel each other out.
Edit: I think I found the author: https://en.wikipedia.org/wiki/Charles_Fran%C3%A7ois_de_Ciste...
His wikipedia page seems to confirm he discovered there are two kinds of electricity and named them "vitreous" and "resinous".
fellerts
Funnily enough, we still don’t fully understand the mechanism by which static electricity is built up when rubbing things together. Professor Merrifield covers this in a very approachable way here: https://youtu.be/0UZb07imNLU. Skip to around 6:00 (or watch the whole thing, it’s well worth it)
do_not_redeem
> We say B is electrised positively; A negatively: or rather B is electrised plus and A minus ... These terms we may use until your philosophers give us better.
I can relate. This is just a quick hack to get to production, we can always rewrite it later!
saghm
As usual, xkcd has a relevant comic about this: https://xkcd.com/567/
card_zero
Found it from the horse's mouth, finally: "We rub our tubes with buckſkin".
https://archive.org/details/experimentsobser00fran_0/page/17...
Don't know where Randall get "silk" from.
jeffwass
But that’s because of historical precedent, if you weren’t aware of this then congrats for being one of today’s lucky 10,000!
Ben Franklin arbitrarily picked the positive anode as the starting point when coming up with the idea of electricity flowing, long before we had any understanding of atomic theory.
It wouldn’t make sense to just invert everything after we discovered that electrons are the actual fundamental charge carriers.
kqr
> about flow of energy going from + to - is the idea of "electron holes" flowing
You mean flow of charge.
My favourite thing about electricity is how the actual energy is transferred on the outside of the wires, in both the directions of positive and negative charge. Resistance is the portion of the energy that accidentally enters the wire. The energy flux inside the wires -- and on the surface of the wires -- is zero. Just outside their surface it is very high.
A capacitor wouldn't work if the energy came from its poles. No, the energy used to charge it enters from the side. This is so counter-intuitive!
null
marcosdumay
Charge flows on the same medium as energy. There's current on the equation of electrical power for a reason.
That bullshit model about electricity flowing around the wires is good for generating Youtube engagement, but it doesn't represent the actual physics, makes things impossible to calculate, doesn't lead to any intuitive understanding, and makes things impossible to learn. Or, in other words, the model is bullshit.
DC current flows entirely in the wires (up to at least "parts per billion" precision), as does energy, because energy flows at the same place current flows. AC current leaks. Everybody knows that, how it leaks is well known, and there are plenty of resources to calculate almost everything around it.
benterix
> accidentally
Well, we may see it this way, but there's nothing accidental in it, it's juts an inherent property of every conductor (except superconductors).
snailmailstare
I had a similarly funny discussion with a proper engineering student on refrigeration insulation and why it isn't more natural to express it similarly with temporarily trapping cold given the inevitable nature of heat/entropy.
criddell
I remember when I was very young I asked my dad if a refrigerator works by moving cold into the box or heat out of the box and he told me it was the latter. It’s a strong memory because he also said something to the effect of that being a good question and at that age, comments like that had an impact on me.
ysofunny
It seems to me like it's an artifact of how it was all discovered and initially implemented.
like scientists didn't realize electrons were flowing in the opposite direction, but engineers already had working electrical devices
choxi
It’s weird in semiconductor physics too because the electrons flow uphill through voltage potentials
at_a_remove
I have expressed this repeatedly: the assignation of a negative value to the electron and a positive value to the proton has probably slowed humanity by a decade.
dotancohen
Anybody who needs to know this detail to design or repair a device, already knows it. There are no simple enough devices where this is relevant for casual repair or modification. You can fix your DC devices such as cellphones and your AC appliances such as refrigerators, and even design your own phones and refrigerators, without knowing in which direction the fundamental particles flow.
srean
Could you give one example
nayuki
> what is electricity?
My favorite answers are:
* http://amasci.com/miscon/whatis.html
* https://blog.rootsofprogress.org/the-significance-of-electri...
k__
I got told what electricity is in primary school, in middle school, in high school, and in university.
Every time I understood it less.
I even watched some videos where people interviewed physics professors, to explain what it really is, and the explanations only got more convoluted.
Seemingly not because those people were bad at explaining, but because if you want to explain it as correctly as possible, it just isn't intuitive at all.
kzrdude
AlphaPhoenix's measurements, experiments and visualisations really help! They show some things that are normally not even taught and even electrical engineers will appreciate to see this. This video he made about it is very good, and worth watching if you wonder about how electricity propagates from one end of a conductor to the other.
criddell
And at each level the degree of confidence seems to be dropping. When you get to the point where the explanation includes an electron being made from a changes in a quantum field and a quantum field is probability, it starts to feel like there’s nothing underpinning reality.
ekianjo
it's confusing because all of the words we use in the field make it seem like it's akin to water flowing (current) whereas the physical phenomenon is far beyond the movements of individual electrons.
H8crilA
The problem with (or the advantage of) the water flowing analogy, or even more broadly the discrete element model, is that it explains reality good enough to be used in most practical situations. Schematics are ubiquitous, yes they are "fake", but they are also usually "correct enough". Kind of like the incorrect Bohr's model of electrons orbiting the nucleus actually does explain the emission spectra (up to a point).
But there is an accessible video that explains electricity pretty well. Veritasium - The Big Misconception About Electricity: https://www.youtube.com/watch?v=bHIhgxav9LY
There is one commonly used concept that requires understanding electricity correctly, and not just as a combination of waterhoses and gizmos. It's impedance, and it directly corresponds to the "controversial" experiment that Veritasium is proposing in his video. Impedance breaks the pipe-of-electrons analogy.
srean
It's not a bad analogy if you also consider the pressure wave. That travels a whole lot faster than the water molecules.
benterix
> The field propagates at close to the speed of light in vacuum (circa 300,000 km/s); individual electrons in a copper wire typically slither at speeds measured in centimeters per hour or less.
It would be worth mentioning why it happens as it's quite interesting.
karaterobot
This was pretty clear and readable, I guess. But the most succinct explanation of electricity that I know of is from Stephen Leacock:
> Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it.
And that's sort of all I need to know.
jvanderbot
> Pay no mind: it’s enough to say that most nuclei on Earth were formed through nuclear fusion in stars and won’t undergo any change on the timescales of interest to electronics — or to terrestrial life.
It's impossible for me to understate how awesome this is. And how hard it is for me to truly grok.
frutiger
Yes, and in particular that it's in all the "ordinary stuff" around you - wood, air, glass, sand. Reality is truly extraordinary upon any closer examination.
iandanforth
For introductory articles like this I also find it helpful to know that the whole positive / negative thing is arbitrary. In fact the assignment of "negative" to electrons arise due to a mistaken interpretation by Benjamin Franklin of one of his experiments. So if you're wondering why gaining the primary mobile charge carrier makes things more negative blame Ben Franklin!
FabHK
I wouldn't call it "mistaken". It was an arbitrary choice at the time, nothing but a naming convention.
Xcelerate
> Most simply, it [electron] just exists as a particular distribution of an electrostatic field in space.
Best simple description of an electron I think I’ve heard yet. I wish we would drop all the dumb analogies. From a kid’s perspective (at least what I can recall from high school), these macroscopic analogies mislead you into thinking the laws of physics work differently than what humanity’s best models of physics actually predict.
For instance, I never liked the sense of “arbitrariness” I felt while learning about the periodic table in K-12 school. The diagonal rule. Hund’s rule. The exception to Hund’s rule. And so on. Don’t even get me started on organic chemistry. But if someone had told me “Forget about billiard balls and wave/particle duality. Our best models consists of solutions to simple and beautiful equations that are extremely difficult to solve”, then that would have made a lot more sense to me.
The author of the article describes the truth as “weird math”. I don’t think that’s necessarily the case. Unitarity is aesthetic—it just “feels right”. The correspondence of atomic orbitals to irreducible representations of symmetry groups is beautiful. Why don’t we teach that to kids? You don’t have to go into the mathematical details of group theory, but just let them know these odd shapes originate from symmetry constraints. Much better than my reaction to seeing an illustration of a d_z^2 orbital in high school. I remember thinking “What the heck is that? This subject makes no sense.”
FilosofumRex
Like all simple description it's wrong. It [electron] is a quanta of the electron field which is a fermion matter (spin 1/2, therefore is charged) subject to the Pauli Exclusion principle.
Electromagnetism is one of the four fundamental forces mediated by photons which are its basic quanta and is Bosonic field (spin 1) and therefore are neutral.
The interaction of these two fields is depicted via Feynman diagrams.
Macroscopically observed Electrostatic field of a charged capacitor, is mediated by the superposition of virtual zero frequency (ν = 0) photons, which are off-shell and non-radiative. Field’s energy arises from the cumulative effect of infinite virtual photon exchanges. Whether virtual photons are "real" is debatable and confuses those who prefer intuition to computation.
fc417fc802
> I wish we would drop all the dumb analogies.
They're incredibly useful tools for thinking about things. You don't need or want QM to perform most reasoning tasks. Even MO is often overkill.
I agree though that we should lead with the truth - that these models you're being taught are useful abstractions but ultimately wrong. That each successive model brings with it more accuracy and nuance but is more difficult to comprehend.
A particular strength of that approach is that after making it to QM at the end it leaves you wondering what's next. It really drives home the point that the map is not the territory and that all we as humans can ever actually have is a succession of maps.
> Forget about billiard balls and wave/particle duality.
Actually that one is rather important. QM wave functions really do collapse. Things really do switch from behaving like a wave to behaving like a particle. This fact has significant effects on behavior.
> these odd shapes originate from symmetry constraints
Well they might fit those constraints, but can they really be said to originate from them? Is there actual cause and effect there? The answer to that would require understanding what gave rise to the phenomenon to begin with.
spacedcowboy
All of education is “lies to children”. Those lies start off as brazen untruths, designed to get the basic concepts across, and then we, iteratively, make things more and more accurate as time goes by. Eventually, if you go far enough in a particular discipline, you’ll reach the boundary of our knowledge, and that’s when things start to get “fun”.
I did a physics PhD. I still never got a really good answer to a question I asked in year-1 senior-school (11 years old, for non-Brits)… “What, exactly, is a positive charge ?” The waviness of the hands diminished over time, but it never really went away.
eszed
The lie I was told: "it has more electrons than it can stably accommodate, so it will give some up to anything around that can accommodate more°".
What's the next level where that breaks down?
°Though the Benjamin-Franklin-reversed-the-signs thing I learned about for the first time up-thread has me thoroughly confused. Positive charge means it... Has fewer?
aeonik
I agree that we should teach the quantum basis of things earlier. I just think a lot of people don't know it, and we don't have a good curriculum for kids to start with.
We'd also need to revamp some of the math, chemistry, and physics curricula to build on the quantum basis of things.
null
srean
When I was taught the planetary model of atoms I was quite suspicious. My reaction was - you can't be serious ... to ... are you making fun of me ... to... just because you have a hammer ...
Few years later orbitals were introduced as, essentially, motion blurs formed by our little zippy guy. I approached our teacher and asked what if that 'motion blur' is all there is and that billiards ball electron is just a bed-time story. That's an adequate way to think he said. Electron mass gets more difficult to explain to school kids in this line of thinking.
simpaticoder
Great article! I particularly like this paragraph:
>It’s important to note that while the charge equalization process is fast, the drift of individual electrons is not. The field propagates at close to the speed of light in vacuum (circa 300,000 km/s); individual electrons in a copper wire typically slither at speeds measured in centimeters per hour or less. A crude analogy is the travel of sound waves in air: if you yell at someone, they will hear you long before any single air molecule makes it from here to there.
So basically electricity flows like a Newton's cradle. But this leaves one nagging question: what is the nature of the delay? This question also arises when considering the microscopic cause of index-of-refraction for light[1]. If you take a simple atom, like hydrogen, and shine a light on it of a particular frequency, I understand that the electron will jump to a higher energy energy level, and then fall back down. But what governs the delay between these jumps? And also, how is it that, in general, light will continue propagating in the same direction? That is, there seems to be some state-erasure or else the electron would have to "remember" more details about the photon that excited it. (And who knows? Maybe the electron does "remember" the incident photon through some sort of distortion of the quantum field which governs the electron's motion.) The same question applies to electron flow - what are the parameters that determine the speed of electricity in a conductor, and how does it work?
1. 3blue1brown recently did a great video describing how light "slowing down" can be explained by imagining that each layer of the material introduces its own phase shift to incoming light. Apparently this is an argument Feynman used in his Lectures. But Grant didn't explain the nature of the phase shift! https://www.youtube.com/watch?v=KTzGBJPuJwM
marcosdumay
> But what governs the delay between these jumps?
What governs the delay between one ball hitting the cradle and the opposite ball going up?
It's the electrical equivalent of the same thing. Specifically, electricity is delayed by the material absorbing it "elastically" for a short time before emitting it back. This is usually modeled as a capacitance and inductance on the medium.
> And also, how is it that, in general, light will continue propagating in the same direction?
It actually doesn't. It mostly follows the medium. That's why you can bend your wires and they keep working.
But if your question is why it doesn't go "backwards", they go, but there's an electrical potential there pushing your electrons on the other direction.
null
A point not mentioned by the article: the electrons in a metal at room temperature are already moving very quickly due to their thermal energy (at the order of 100km/s) — much faster than the speeds quoted in the article, which is what's called the "drift velocity".
This thermal motion is essentially random, and the electrons constantly scatter off the nuclei every which way, so it cancels out and doesn't create a net current.
So, it's less than the electrons gently move under the influence of an electric field, and more that it introduced a slight bias in the existing thermal motion.
E: To clarify in case it may have been unclear, this is unrelated to the speed of propagation of the electric field, which as the article says is the speed of light.