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Electrons are round!

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TimFox:

--- Quote from: gnuarm on August 15, 2023, 01:39:36 pm ---
--- Quote from: radiolistener on August 15, 2023, 01:17:09 pm ---
--- Quote from: TimFox on August 14, 2023, 11:32:32 pm ---mm2, the common wire size in metric-speaking countries, rather than mm diameter, since I have had technical conversations with foreign engineers who used "mils" or "mm" as an abbreviation for area.

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cross section area in mm2 is commonly used for high power electricity, such as mains lines, power cable between mains socket and high power equipment, etc. When you deal with more precise electronics, for example hand made RF inductors, transformers, in these area diameter in mm is commonly used...

For example bobbins with copper wire for inductors and transformers are marked with mm diameter. I don't remember bobbins which was marked with cross sectional area in mm^2.

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I can't recall specifics, but when I look for info on wires, I seem to recall the use of terms which are not properly electronic.  It's as if the electrical world tossed out all the info on units and just invented their own.  So, I think there is a unit they use for area, which reads like a linear unit, circular mils, perhaps?  This gets shorted to just mils in tables.  Maybe that's also true for mm?

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An American conventional unit (inch based) for wires is the "circular mil", which is defined as the area of a circle that is one mil in diameter, where one mil = 0.001 inch.
It is often found in design rules or rules-of-thumb for recommended current density in transformer windings, etc., in amperes per circular mil.
The American "AWG" gauges for wires, typical for "gauges", is a logarithmic measurement rather than linear measurement, where a difference of 3 in AWG is close to a factor of 2 in area: AWG 20 is 1,022 cir mil and AWG 17 is 2,048 cir mil in area.
My mnemonic is that AWG 10 is 0.1019 inch diameter, close to 1/10 inch.
For very large wires, larger than AWG 0 (sometimes called 1/0) = 0.3249 inch diameter or 106,000 cir mil area, the conventional series proceeds to multiple 0's: 00 (2/0), 000 (3/0), and 0000 (4/0).
Thereafter the amusing abbreviation "MCM" for "thousand circular mils" (as in the ancient Roman numeral M = 1000, not the modern mega).
I first ran into this when observing the installation of a new electrical box fed by "250 MCM" wire (0.5 inch diameter), the next size up from AWG 0000 at only 212,000 cir mil area.
Now, the skin depth of copper at 60 Hz is approximately 8.5 mm = 0.335 inch (depending on alloy), so one reaches diminishing returns in AC resistance per price of copper for solid copper wires above that diameter.
I believe that the maximum copper wire diameter in that series is 2000 MCM (1.414 in = 36 mm diameter).

AVGresponding:
There's a certain laziness in referring to the size of cables in mm2 by just using "mils". I have to confess I am sometimes guilty, as are all my colleagues, from time to time...

TimFox:

--- Quote from: AVGresponding on August 15, 2023, 04:48:22 pm ---There's a certain laziness in referring to the size of cables in mm2 by just using "mils". I have to confess I am sometimes guilty, as are all my colleagues, from time to time...

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As I have mentioned elsewhere, I fell into a technical misunderstanding when a UK engineer asked me if "4 mil" wire were adequate for a power connection, and I thought he meant 4 mm diameter instead of 4 mm2. 
I did a rough calculation based on my mnemonic that AWG 10 was 0.1 inch diameter, knowing that the current rating of AWG 10 is 30 A.

edit:  corrected typo

radiolistener:

--- Quote from: TimFox on August 15, 2023, 01:50:02 pm ---Yes, the usual understanding is that the electron is a fundamental particle with no structure.

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in reality no one knows what is electron and if it exists at all, we just using different physics models that can predict behavior in some cases, but there is no model which explains all details about electron. Some models represents electron as particle, some model represents it as wave, but we don't know what is it exactly :)

TimFox:
I have had experience with electrons in vacuum (CRTs, particle accelerators, vacuum tubes, radioactive beta decay) and know that they exist.
In my view of physics, "particle" and "wave" are mathematical descriptions of the behavior of entities, analogous to billiard balls and ocean waves in much larger macroscopic contexts, that quantum mechanics' rules dictate how to calculate their properties and motion.
Note that "model" and "theory" are not bad things (like in the vulgar usage "just a theory") in science.
In this particular discussion, the experiment is testing models that assume no structure (zero moment).
In another recent experiment, measurement of (g-2) in muons (heavier leptons with short lifetime) tests if the currently accepted "standard" model accurately models the interaction of the muon with a host of other particles (real and virtual) buzzing around it.

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