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Re: [Amps] "Conventional" current flow

To: amps@contesting.com
Subject: Re: [Amps] "Conventional" current flow
From: Manfred Mornhinweg <manfred@ludens.cl>
Date: Sat, 03 Dec 2016 15:18:14 +0000
List-post: <amps@contesting.com">mailto:amps@contesting.com>
I can't like that model of the electrons moving slowly but the charges moving fast. When it comes to simplistic models, I much prefer the one I saw in the instruction manual of a didactic toy, when I was 8 or 9 years old and learning electricity. The author of this manual modelled the electrons in a wire as the cars of a train. As every open-eyed child in those years had surely observed on more than one occasion, when the locomotive starts pushing at the end of a standing train, the next thing that happens is a fast clack-clack-clack, as each car strats moving, takes out the slack in the joint to the next car, and then that next car starts moving too. The frontmost car starts moving very briefly after the locomotive starts pushing, which of course does not mean that the last car moved fast to the position where the front one was!

So, the MOTION propagates fast along the railway track, while the individual train cars move slowly. Just the same as in the wire. And the charge, or load, is transported by the cars/electrons. Since the charge of each is the same, it doesn't matter whether at the end of the wire we get the same electrons we put in at the other end, or other electrons.

The same fast motion propagation happens, of course, when the locomotive pulls instead of pushing, and this fact was used in the booklet to make clear that electrical phenomena are independent of which way we prefer to think about them.

About the actual average speed of electrons in a wire, when using a simplistic/mechanical model, it's of course totally variable, and depends on the current density in the wire. One can compute it by calculating how many movable electrons there are in the metal, per length of wire, and dividing the current, expressed in electrons per second rather than in ampere, by this number.

And about more advanced models for physical phenomena, including electricity, I don't think that our current knowledge of quantum electrodynamics is the last word that will be spoken on the matter. It's just one more step in the ladder towards a definitive, complete understanding of physics - which humankind might never achieve.

For the time being, we should be best off by using the simplest model that adequately explains and predicts results for each particular situation we have at hand. And we should be aware that these are all models, not the real thing. And that scientists are gradually getting closer to the real thing, but are not yet there.

Manfred


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