Visible light is in the electromagnetic spectrum, with certain wave lengths and frequencies, carried by the photon vector. However, other than theoretically traveling at the speed of light (which, I know, it does not actually do), and acting as waves in some situations, I see no relationship between electricity and light. Electricity does not have the photon vector, and is carried by electrons. This is something that I should have learned years ago. Electricity waves are not in the electromagnetic spectrum.
What about Radio, then?
At a very basic level, electrons—anything with a charge, really—generate electromagnetic fields. Moving an electron around generates ripples in that field. Periodic ripples in that field are electromagnetic waves. In the right frequency interval, those waves interact with receptors in the eye, and hence, we see them as light. At frequencies that are too low, we go into the infrared, microwaves, radiowaves and so on. At frequencies that are too high, we have ultraviolet, x-rays, and gamma rays.
What about radio? It is in the electromagnetic spectrum and is carried by photons. it has the lowest frequency (lower than microwaves) and longest wave length in the electromagnetic spectrum.
So you are saying that electricity generates waves with photon vectors, but we do not see them as visible light? Infrared radiation, perhaps, which is heat?
Nor did most people for a long time. If it was obvious, then Maxwell would not be so celebrated.
OK, the average home I actually care about has electricity going through its wires in a simple rhythmic motion, forwards and backwards, with the electrons largely returning to their original locations sixty times per second. That’s a 60 Hz alternating current.
Every electron is coupled to the electromagnetic field. An electron standing still or going at a constant velocity relative to you has straight, smooth field lines, which can be traced back to it smoothly as long as it maintains its constant velocity.
When you accelerate an electron, the field lines coming off that electron kink. They bend to point to the new position of the electron, now that it’s changed velocity. Those bends propagate outwards at the speed of light like ripples on a pond. That’s electromagnetic radiation. Those bends induce other electrons to move in a way proportional to the bends’ size and frequency. We sometimes think of those bends as being made of particles called photons.
Thus you can see that the 60 Hz alternating current produces electromagnetic radiation every time the electrons in the wires change direction. All of the wires in your house’s walls are radiating at 60 Hz as long as the power to your house is switched on. You don’t notice this because energy is directly proportional to frequency, and 60 Hz is extremely low frequency. Your body really doesn’t have anything in it which can respond to a wave with as little energy as that. You’d need something like a piece of metal to detect it, because metal has a lot of loose electrons in it, floating around, capable of being pushed this way and that by just about any passing wave in the electromagnetic field. Therefore, you can sometimes hear the 60 Hz radiation as a low hum in a speaker system which isn’t built very well.
So the electricity carried by overhead wires before they enter my house are traveling faster than 60 Hz and have much greater voltage, and hence that is the reason I can hear them hum?
The overhead wires are still using a frequency of 60Hz, but much higher voltage and current. The reason you can hear a hum from them is because the electromagnetic radiation causes metal components (primarily transformer boxes) to vibrate at just about 60Hz. The (relatively) small amounts of electricity in your house don’t have enough energy to vibrate nearby metal, but the same principal is at work.
It’s all the same frequency, but you’re correct that power lines carry electricity being shoved along at about a thousand times greater voltage than what ends up coming out of your wall sockets. This is done to reduce losses when transmitting power over great distances. This also explains the transformers: They’re step-down transformers, meaning they take high-voltage low-current electricity in one end and produce low-voltage high-current electricity out the other end.
You hear a sound higher than 60 Hz because they’re making noise twice per cycle, once per peak, which amounts to 120 Hz.
Anyway, there are a few reasons those things make noise. One of the reasons is that the current, at peak, makes the iron core in the center of the transformer stretch a relatively small amount, as the electromagnetic radiation makes all the electrons move in a given direction and the protons (and, therefore, neutrons) get dragged along, meaning the mass as a whole stretches a tiny bit. This is enough vibration to make noise at, as mentioned, about 120 Hz, given a 60 Hz power supply. Similar things happen to the metal enclosure and other metal objects close by.
Here’s a good page describing a few reasons power equipment hums.
One thing to be clear on - a photon is badly named. Whilst the name implies “light” as in visible light - photons interact with charged particles at any frequency, be it a few Hertz in your house wiring, a few kilohertz, in your HiFi, a few hundred kilohertz when you receive AM radio, a few to a few hundred megahertz when you receive a TV signal, gigahertz when you use a cellular radio or GPS, right through terahertz exotica, into heat, infra-red, visible light, x-rays, gamma rays. All photons. But photons with wildly different energies. Indeed the energy of the photon is exactly determined by its wavelength. Most of the time, when working with stuff that is though of as “electrical” we just don’t worry about photons. We can do this because the quantum effects that are so important with light, x-rays etc, are so feeble that they make no discernible difference to the way “electrical” things operate. When we talk about visible light and higher energy (shorter wavelengths) the way things work becomes dominated by quantum effects, and it is impossible not to ignore photons. But from one end to other, it is all about charged particles interacting, and the thing they interact with is called a photon. But only photons with energies in a very limited range can be detected by our eye.
Worth pointing out, the speed that electrons move in a wire is ridiculously slow. This is called the “drift velocity”. What we call electricity travels at the speed that the “shove” travels down the wire. Think of a pipe filled with marbles. Shove one end. A marble falls out the other almost immediately. The shove travelled much much faster than the speed of the marble in the pipe. Photons mediate the shove between the free electrons in a wire. The free electrons themselves move very very slowly.
You can have electrical phenomena without electrons. Two protons, for instance, will repel each other with no electrons present. But you cannot have electrical phenomena without photons. Those protons repelling each other? It’s because they’re exchanging photons.
Up to a point, you’re right. Electricity is the transport of charge: things that are charged move from here to there, or in more subtle cases charge decreases here and increases there, which is effectively the same thing. You can imagine it as the movement of blue-painted things, which you could do by literally moving blue-painted things (rocks, sticks, elephants) or by taking the blue paint off stationary things and putting it on some other things somewhere else.
Light (which I’m interpreting here as “any kind of electromagnetic radiation”) does not itself transport charge, and the transport of charge doesn’t need to result in the creation of light. So from that point of view, yes, electricity and light appear two different things – and so indeed they appeared to early 19th century experimenters.
However, it turns out that all charge creates an electric field, and light is an oscillating (moving back and forth) electric field. That immediately suggests that you can create a connection between electricity and light: for example, you could transport charge back and forth rapidly – wiggle it – and that would make the electric field it generates wiggle – and voila, there you go, you’re creating light. (Or radio waves, of course, or infrared, ultraviolet, whatever you like, depending on how fast you wiggle it.
And while it’s not at all obvious, you might reasonably suspect the reverse process can occur, too. That is, a wiggling electric field (light) could meet some transportable charge (charge that is free to wiggle) and proceed to wiggle it.
An important fact to keep in mind is that the mere wiggling of charge is actually another form of electricity, AC. It seems a little weird that we can (for example) extract useful work from charge that is merely transported back and forth very rapidly, never actually going anywhere, but remember it’s just the energy in the motion of the charge that we want in the end. It’s somewhat like the fact that we can get energy either from a steady flow of water, in a river, but also from the back and forth motion of water in waves (although it’s a little harder in the second case, you need some kind of reversing paddle wheel and complicated gears). It’s the energy of the motion that is important for technology, not the particular kind of motion.
The wiggling of charges to create “light” is what happens in electrically-powered radio transmitters or AC light bulbs. “Light” wiggling mobile charges to create AC electricity is what happens when radio waves meet radio antennas, or when visible light meets the electrons in the visual pigment molecules in your eye.
Electricity does travel at the speed of light.
Here’s the way I like to explain it. Electricity is really the behavior of the electric field. The photon is what carries the electric field. Electron’s don’t carry the electric field - the electric field causes electrons to move. So if you think of electricity as being electrons that are moving, that’s not quite right. Moving electrons are evidence that there is an electric field there.
Here are a couple of lesser-known facts that may help clear it up. First, electrons in a wire actually move very slowly, as in a small fraction of a millimeter per second. So how come when you turn on your light switch, the light comes on immediately, only delayed by the speed of light down the wire? It’s because the electric field moves at the speed of light, even though the electrons move slowly.
Next, what determines the speed a change in electric voltage moves down a pair of wires? Is it the metal that the wires are made of? No, it’s the material that separates the wires, the dielectric between them. If you have teflon around the wires, the speed will be about 70% of what it is with air. If you have water, the speed will be about 11% the speed through air.
So don’t think of electricity as moving electrons, think of it as the electric field, and that then causes electrons to move.
Not the way everyone else uses the term.
That’s entirely at odds with how everyone else defines the term, and it makes nonsense of various terminology. For example, the electromagnetic field has no amperage. An amperage is a flow of charged particles, and photons have no charge, so QED. You can use your terms your way, I suppose, but you’ll have a heck of a time convincing anyone else why you claim there’s electricity in a conductor when the ammeter says there’s no current.
It’s less confusing to think of what’s really going on, or at least some approximation thereof:
The electromagnetic field is everywhere, and is probably best thought of as just a computational tool. It enables us to model all quantum particles as waves using really neat mathematical tools devised by people who had no idea that their Nineteenth Century cathedral of deterministic physics was built on a foundation of amplitudes and scattering and renormalization.
Photons are massless particles. They’re modeled as disturbances in the electromagnetic field which are either coherent ripples or not; if they are, they’re moving in a direction at the speed of light; if not, they’re virtual particles, exchanged between two charged particles. Best description, probably. More information, without any actual math. Textbook. Math. Diagrams.
Electrons are massive particles. They’re also modeled as ripples in the electromagnetic field. They are attracted to and repelled from other massive particles by exchanging photons, which they also do when they gain and then lose energy. This second phenomenon, gaining and losing energy, explains things such as reflection, refraction, and, when the energy gained and lost is momentum due to a voltage change, radiation from an antenna.
Electricity, defined the way everyone else defines it, is flow of charged particles, very often just electrons, but frequently protons (and, therefore, neutrons as well) and electrons at the same time. It’s entirely correct that the drift velocity and the propagation velocity are two separate things: Drift velocity is how quickly a given charged particle moves through the substance (or vacuum, in some cases); propagation velocity is how quickly a signal, such as a change of voltage or current level, will move through the substance.
Every substance is chock full of charged particles. However, some substances hold their particles in place better than others, meaning it takes more force (a higher voltage) to make them move around in a current. The substances with a lot of loose charged particles, such as metals or a good hot plasma, are known as conductors; other substances, like most plastics or dry air or a hard vacuum, are known as insulators. Some insulators, like the plastic, have a lot of charged particles which are really reluctant to move; others, like the vacuum or dry air, don’t really have a lot of particles to begin with. And if it doesn’t have protons or electrons at all, but it’s still solid, it’s not something you’re ever going to see first-hand.
I do want to emphasize that last point: When you get down to it, the quantum theory behind how electricity and magnetism work describes the vast majority of everyday life which isn’t either gravity or sunshine. It describes all chemical bonds, all radiation, visible and otherwise, and the vast majority of the behaviors of bulk matter, such as why solids are solid. Quantum Electrodynamics is one of the crown jewels of all science.
Although moving charges cause electro-magnetic ripples, it’s interesting to note that the ripples themselves are not “radiation”. You do get some “radiation” from your power wires, but it is tiny, and it is tiny compared to the charge, and it is tiny compared to the electro-magnetic ripples caused by moving the charge.
“Radiation” is when energy actually leaves the system, and goes somewhere else. The sun radiates heat and light to us. Radio transmitters radiate EM waves (photons). Cell Phones radiate EM waves (photons). Your power lines would be lucky to radiate anything.
Electrons have a static electrical field. When your power company pushes electrons into a wire, they push other electrons out around the circuit and back in the other wire. The electric field is what does the pushing – the electrons never get close enough to each other for the atomic forces to come into play. Because it is the electric field which is doing the pushing, the pushing does happen at “wave speed”, and is constrained by the same forces which constrain light. But you’re right: it is not light. It is not Electro Magnetic Radiation. It is a related phenomenen, called “near field radiation”.
No, they’re ripples in the electron field, which is a completely different field than the electromagnetic field, and basically never encountered except in those ripples.
This has always made sense to me (at least as far as something I don’t understand at all can make sense :eek: ).
But what about opposite-charged particles attracting each other? How do you explain that with photon exchange? I see at stackexchange that others are also confused and long eyes-glazing-over answers are available online, e.g. at math.ucr.edu/home/baez/physics. But is there a very simple explanation for simpletons?
We did an experiment bouncing a square wave between ends of a coaxial cable in undergraduate school, and determined that it was moving at .8C.
Nothing to add except to say thank you for asking this, and thank youse for answering. I’ve wondered about this myself for many years!