Where do all the electrons come from?

Factual Questions
1

This might be the dumbest science question asked here in a while, but believe it or not, I really wonder about it.

Electricity is a flow of electrons. You setup a potential difference between two points in a conductor and a flow of electrons ensues. Apparently the conductor has free electrons to spare, and these go around.

Questions:

  1. The electrons travel from source to destination and are utilized by end-devices like my laptop. So the source or lender of electrons must be gradually depleted and gain a positive charge because electrons travel away and are lost, in the sense they are no longer associated with the donor. But since we can sustain electricity indefinitely, this is apparently not the case. What’s going on here?

  2. Electrons have mass and so are more difficult to move around than say photons. Why use electrons instead of photons to achieve energy transfer?

  3. Exactly how does an end device use the electrons without acquiring a net negative charge?

(If we are going to run out of electrons soon, we should petition our governments to plan for this contingency.)

2

Electrons travel in a loop. They go in one wire and out the other. Your computer doesn’t use the electrons themselves; it uses the energy that was transferred via the electrons.

3

  1. Electrons aren’t used as fuel; it’s the energy from their motion that is used. Think of water flowing over a water wheel. Electrons travel in circuits (loops) in one wire and out the other. (In AC systems, they reverse direction 50 or 60 times a second, but it’s the same basic idea.)

  2. Precisely because it takes energy to move them; this is the energy that we extract to power our devices. Photons don’t carry as much energy. But we can use them to transmit information very well (fiber optics). And if we’ve got a whole lot of photons we can use them to make electricity (photovoltaics.)

  3. It doesn’t. The end device uses the moving electrons for energy; this adds resistance to the electrons’ movement. The more resistance, the harder the generator (or battery) has to push the electrons.

4

Think of a bicycle chain. The chain moves from energy imparted by the rider, but isn’t used up. Electrons in a wired circuit move similarly, jumping from atom to atom, moved by energy from a generator or battery. There is no net loss or gain of electrons.

5

your questions 1 and 3 are roughly the same issue, and here’s your answer:

for a battery, there’s a salt bridge between the anode and cathode that fixes for the electron-loss you’re talking about, to put it in your words.

Most little batteries acualy arent designed with a salt bridge, but the cathode, or is it anode? doesn’t get used up, it’s a piece of carbon. Feh… did you learn about batteries in high school yet? They go over all that stuff. Look it up online, you’ll see diagrams, and it’ll show all the ion exchanges at all the relative points.

For generator-produced electricity (like on the grid, you know, in your house), the voltage or electromotive force (emf), is produced mechanically by moving wire loops through magnets, which induces a an electric field and thus a voltage that pushes a current in the wires. The elctrons just go in a full loop.
as per your question 2, you’re taking vague descriptions on what we sort of know about subatomic particles and applying it weirdly using classical mechanics. Nobody “decided” to move electrons instead of photons. The phenomena of the battery and Faraday’s principle (generators) were all discovered independently before the later subatomic explanations of photons, electrons, protons, neutrons, and even ions, etc. All these explanations came later to describe all the phenomena we had discovered in physics. But even now, our “knowledge” is really fuzzy on these particles; the experiments we can perform show wackadoodle behavior from all these particles, showing they also act like waves, and quantum mechanics lets us make predictions in certain experiments, but also fails to give any description as to what’s going on between electrons and their nuclei they’re “orbiting”. Are they orbiting? If they are, why aren’t they radiating? etc.

What you need to know is that this dude once stacked nickel, copper, and cardboard soaked in vinegar, and thus invented the battery. And then later another dude noticed a compass getting deflected by a current, and then we ll figured out that a changing electric or magnetic field induces the other kind of field at a right angle, and then somebody was like “hey, let’s spin wires around next to magnets, and wel’ll be able to get elctricity!” and then provided power from a source other than a battery was born.
From there, the thing to remember is that The reactions that occur in the battery are well described by physics and the equations balance, and you can learn them, and so are the equations that can tell you how strong a generator design will be.
That’s what you need to remember, and learn if you haven’t yet

6

Tue for DC. But what about AC? :wink:

Now let’s say I have a flashlight. (DC, obviously.) We can all agree the electrons are moving in the wire. We can also agree the electrons are moving through the bulb filament. But are the electrons moving through the battery, too? I have always been under the impression that the mobile charges in a battery are ions, not electrons. If that’s the case, what happens to the electrons in the wire when they reach the battery’s positive terminal? Do they disappear? Or recombine? How are “new” electrons created at the battery’s negative terminal?

7

@ crafter man

again, salt bridge.
Yes, the electrons are coming off of the chemical compounds, and then going into the wire and pushing the rest of the electrons, causing all of them to move.
At the other end, electrons are also being chemically received into chemical bonds/electron shells

I forget how actual little batteries work, I just remember the equation balances, and there’s a carbon anode or cathode, I can’t remember which. Once you understand it, it isn’t hard to understand once you look it back up in your text book

And oh yeah, we forgot to tell him AC. With AC power, the electrons are moving back and forth.

8

Its the build up of electrons, the net oversupply or undersupply, that drive the circuit, not individual electrons. That is, in practice , you don’t just pick one single electron and follow it . You would see it buzz around a 10 trillion times (or some crazy number) backward and forward before you see it do a lap of the circuit. The potential differences just maintain an uneven distribution of electrons… a charge…

Any specific electron can jump around between the metal atoms in the battery… l Whats important is that the the excess at the anode remains continuous, and the deficiency of electrons at that cathode remains continuous …
The excess of electrons at the anode is generated by neutral metal atoms becoming ions - anions - and leaving electrons behind on the anode. The metal atoms want to do this… they are pushing for it to happen.

The cathode absorbs electrons when metal ions become neutral with the aid of the electrons from the cathode… This creates a efficiency of electrons at the cathode… which means its happy to take electrons from the electrical circuit (through the load.)

9

It should also be noted that the electrons are moving through the wires very slowly. When I flip the switch in a DC circuit, electrons start moving from the battery into the wire basically instantly, and electrons start coming out of the wire into the bulb, but they’re not the same electrons. Each individual electron moves only a small distance, and the next electron also moves a small distance, and so on, and the net effect is mostly the same as if one electron moved the entire distance, and all the others just stayed in place.

Combine this with the fact that in an AC circuit, they’re changing directions a hundred or more times per second, and the net result is that each electron only ever moves a microscopic distance from where it started.

10

AC comes from generators, which rely on the link between electricity and magnetism.

When a magentic field crosses a wire (as opposed to moving along it) it creates a differential which causes current to flow, until equilibrium is restored. If the magnet or wire are constantly moving, equilirium is never reach and so the electrons keep moving back and forth trying to achieve a stable balance. That’s AC.

That’s grossly oversimplified and probably wrong in some minor details, but it gives you the basic picture.

11

An article from Bill Beaty.

12

Electrical engineering references the movement of electrons in a single direction as an electrical current. Electronic Engineering references current as “holes” which are the atoms missing electrons on their orbits. Either way, metals give up electrons relatively easily while non-metals usually do not (called insulators). Despite what was said here atoms do not give up electrons easily - it takes energy to push an electron out of its atomic orbit (measured in keV). So a potential (voltage) must be supplied before any movement occurs. The resistance of movement causes heat to build up in wires - the more electrons moving the hotter the wire will get. It is not completely a closed loop because energy is lost to heat.

13

Not necessary. AC can come from an inverter too.

14

But is it correct to say that the number of electrons remains the same, but their energy is less due to some of the energy being converted into heat?

15

Umm - this is not entirely true. Metals have free electrons or nearly free electrons.

These free electrons can move about relatively easily within the crystal structure of metals. They are responsible for the good thermal conductivity, good electrical conductivity and “shiny-ness” of metals.

16

Think of electricity moving through a wire - like a wave moving in the ocean - from the middle of the ocean to the shore. The water in the sea is not moving appreciably - but the wave is. Saying the water has less energy at a particular point in the ocean because some energy was lost doesn’t make sense.

17

Some other interesting things to note here :

1> There are two types of velocities moving through the wire (conductor). One the electric field which moves at the speed of light in that medium. The interesting thing here is that the velocity depends on the dielectric constant of the insulation - hence coaxial cables or cables carrying signals pay a lot of attention to this. The drift velocity of the electrons is in the order of inches/hr.

2> Since the best insulation gives around 0.7 the speed of light speed - Fiber optics are preferred for higher speeds. If you want a really fast PC - you’ll need fiber optics hardware.

3> There is very similar behavior in flow of fluids through pipes. As you keep increasing the pressure drop across a pipe, the flow will keep increasing - until you reach a point where the velocity in the pipe is equal to sound velocity.

4> There is another effect called the skin effect- when the frequency of AC (or signals) go higher, this effect comes into play and increases the effective resistance of the conductor.

18

ughhhhh… this stuff is so hard to describe sometimes, especially with questions like this.

for a genny-powered circuit, yes, number of electrons are same. But they never “had energy” in the first place. They flow, compelled by a voltage, often called an “electromotive force”, or something like that. The energy “taken out” by components comes from… well it depends on the component. Motors, for example, use the flowing current to create magnetism, whereas something like a light uses the electro-chemical effect that creates light. These things create are “loads” and their resistance to the current happens for different reasons (in the case of a motor inductance, in the case of a light resistance).

Really, the best way to understand it is as a water-pipe analogy. A water system could power any number of machines, but the power doesn’t “come from” the water, it comes from the water pressure, and how much power can be provided from there depends on the flow rate. The speed of the water itself is not really consequential; The whole system moves instantaneously (well, with a centrifgal pump maybe not, but instead imagine a cylinder pushing water in a pipe by displacement. On the other end, no matter how far away, the water would start advancing instantaneously). The actual speed of electrons is slow
But over all, it’s important to remember that these are subatomic descriptions of what might be happening that science came up with AFTER THE FACT. The PHENOMENON of electricty and current flow was discovered long before that, and directly it’s the only thing we “know”. You could kind of say that about any phenomenon, but then we’d be getting into a discussion of epistomology and science (or would it be metaphysics?) Don’t think of it in terms of electrons moving, think of it in terms of volts, amps, whats, and hertz, that’s it.

19

I’m sure what the article says is mostly true, although some diagrams would have helped. It’s just unfortunate that so much of the article is wasted in enumerating all the ways in which other people’s conceptions are Wrong, False or Misleading.

20

Bill Beaty: He’s getting really pedantic with this one:

“HE STUFF THAT FLOWS THROUGH WIRES IS CALLED ‘ELECTRIC CURRENT’”