ECN Forum Forums Technical Discussion Electrical Theory and Applications Do electrons Oscillate?

Dnk - In most materials, the orbiting electrons are tightly bound to their central nucleus, and it is only with great dificulty (i.e. exceedingly high pressure) is it possible to occasionally pry one away from it's atom. Naturally these materials are poor conductors.

In a few materials (i.e. good conductors) the electrons in the outermost orbit are loosely bound. So much so that they occasionally wander off by themselves, even with no external pressure applied. Thus, we have materials that have some quantity of "free electrons". These electrons can leave their orbits, wander around a bit, end up falling into another atom's orbit, any number of things. They are also readily available for current flow, should the opportunity arise.

Lastly, there are some materials in which the outermost electrons are bound neither too tightly nor too loosely. These materials do not have a lot of free electrons, but if sufficient pressureis applied (and a flow path provided), electrons will be moved from their orbits and form a flow of current. This stuff we refer to as semi-conductor material (not semi-conductor devices).

By the way, the spot in the outer orbit of an atom that is vacated by a renegade electron is called a "hole". Holes have positive charges, since the negative electron is gone, and can be observed as traveling in a direction counter to the direction of electron current flow. The holes don't actually move, or flow, but as electrons move from one orbit to another, then on to another, the holes give the appearance of moving the opposite way. This is important for reasons that I'll pretty much ignore for the moment.

Interestingly, it is possible to chemically alter semi-conductor materials (with neither too strong nor too weak electron binding), and sort of inject the material with an excess of electrons or and excess of holes (electron deficiency). By combining these altered materials in different ways, semi-conductor devices are produced.

Scott mentioned something about anyone seeing an atom to please report - they haven't and they won't. Even relatively big atoms are far far smaller than the wavelength of anything we could use to observe them directly. So we live with having to try to detect the predicted effects, and trying to minimixe the effect of our observation on the results of that observation. Very dificult.

To put this in some small degree of perspective, you'll remember from basic E&E that 1 amp of current is equal to i coulomb of charge per second. So what is that? 1 coulomb = 6.28 x 10 ^18 (10 to the 18th power). That is 6,280,000,000,000,000,000 or 6.28 billion-billion electrons past a given point in 1 second. 2 amps is twice that many, and so on.

Kind of makes you wonder, who counted them? And who came up with the right spin and left spin of electrons (more on that later).

Radar

A quick word or two about electron “bumping”. We know a couple of things about electrons, that 1) they have relatively strong negative charges, and 2) that negative charges repel one another. So if you tried to shove electrons into a pipe like our billiard ball analogy, the negative charge would make each one appear much larger than it really is, and there would be lots of space between them. The overall effect would still work, each electron pushing the one in front with it’s repelling force, but no actual bumping.

Something that amazes me – if a modest sized atom were expanded in our imaginations to the point that the nucleus were the size of a bowling ball, the nearest electron in the very closest orbit would be represented by a B-B that is a mile or 2 away. Outer orbits are further away yet. And in real life materials, even though atoms are linked chemically, the negative charges of the orbiting electrons maintains lots of space between atoms. So what we see as solid objects actually consists of vast amounts of empty (micro) space.

Radar

Quote:
"Logic tells us that current flows, so by the process of elimination, it should be somewhere between zero and 186,000 miles per second."

This basically allows me to state an obviously worthless opinion without fear of being wrong. ( I love quoting myself )

Quote:
"What I'm getting so far, is that with a pressure (voltage) applied, electrons would wobble, oscillate, gererally move around inside the conductor, without a complete path to generally flow."

Basically, yes. When a froce is applied to a conductor, there doesn't have to be a complete path for current flow.

The prime example of this is the charging of a capacitor. When voltage is applied (let's assume a DC source for this), the electons are forced to one end of the circuit while the "holes" (as Radar pointed out) go to the other.

( At this point it is important to remember that "hole" does not refer to your supervisor).

During the time that it takes the charges to go to their respective end points, there is "current flow". Once the charges at the end of the circuit equal the charge that created it (a battery for instance), the current flow ceases.

If you could drive your car at the speed of light, would anything happen when you turned the headlights on?

Boomerang: If you could drive your car at the speed of light, would anything happen when you turned the headlights on?

It doesn't matter because you're driving too fast to avoid the deer even if you did see it.
Joe

A copper atom has 29 protons at it's center, and 29 electrons orbiting it at different layers. The layers are kind of like the planets orbiting the sun. The different layers have different numbers of electrons, but the outer layer only has one electron. And since it's the most outer layer, that electron has the weakest hold on it by the ptotons. With no voltage applied to the conductor, and when these outer electrons are influenced by another attraction, it will drift away from it's atom and become a free electron. It will then drift around until it attaches to another atom's vacant outer layer. When AC voltage is applied to the copper wire, the electrons move in a specific pattern. On the high side of the sine wave, the electrons will move forward to the next atom, and on the low side of the sine wave, the electrons will move backwards to the next atom. This is current, and this forward and backward motion is what I've always heard called oscillating, or vibrating. Also, the electrons do not move through the conductor like the pool ball description. The elctrons acually only move back and forth in a distance shorter than a ten-thousandth of a millimeter. It is the electrical energy that moves forward through the wire at the speed of light.

What makes a big difference here regarding oscillation is whether we're talking AC or DC. In 60 cycle AC, as Edge touched on above, electrons move in a particular direction (towards the positive) for only 1/120th of a second, then they reverse direction (because the positive has moved) for another 1/120th of a second. How far they move in that time? Who knows? Probably not very far. I don't know that I'd call this motion vibration exactly, it's just changing direction 120 times a second - but call it what we will.

In DC it's a little different. The direction of the positive does not change, so electrons all travel the same direction as long as the pressure is applied. Some will sort of leap-frog from one orbit to another, some (free electrons) may simply bumble along as part of the general flow.

The lone electron in the outermost shell of a copper (or gold or silver) atom is interesting in that although it balances the atom electrically (equal number of protons and electrons), atoms in general do not like having 1 electron in the outermost orbit. The result is a quantity of free electrons in copper, unbound electrons that have simply drifted away from their orbits. Of course they might fall into another orbit, but at any given time there are lots of free electrons. That's what makes copper a good conductor.

Radar

Maybe we should just cut to the chase and forget about this theory stuff. Let's make it simple and just mark one electron with an indelible magic marker that won't rub off and either watch it or put it in one end of a wire and see if it comes out the other end. If you measure the wire and have a stop watch you can figure out how fast it goes.
Just a little humor to lighten thing up a bit.

I'm thinkin' I'm gonna be needing a new Sharpie.

I'm still grappling with WFO's 'holes' moving to the other end of a conductor!

Alan