Some time back Dave pointed out that for most practical engineers it doesn’t matter. I'd agree with that. But it may or may not matter, it depends on the situation. It matters very much to ic designers and semiconductor physicists.
No it never matter.
Yes, that which we call Ohm's Law is a result of the scattering of electrons by lots of things in a conductor, so that they do not achieve a high velocity from the voltage gradient along the wire.
An example calculation in https://www.macmillanlearning.com/studentresources/college/physics/tiplermodernphysics6e/classial_concept_review/chapter_10_ccr_10_mean_free_path.pdf gives a mean free path between scattering events for electrons in copper as 0.39 nm.
This is completely incorrect.
https://homepages.rpi.edu/~galld/publications/PDF-files/Gall-116.pdf
Indicates 39.9 nm.
He assumed that electrons scatters with atoms, while they scatter with phonons.
Yes, there are lots of things inside a conductor to scatter electrons.
In grad school, I learned about phonons, lattice imperfections, and other defects as contributions to limiting the conductivity.
Note that, in general, alloys (which include impurities) have much lower conductivity than pure metals under normal conditions.
Yes, but alloys in wires do not affect the speed of the electons (electricity) on the surface of the wire.
So tell me: why does the alloy composition affect the conductivity of current down the wire?
Yes, good question, it is so good (& obvious) that it must have kumup earlier here, i forget.
Elektons have a nett E×H field (in the nearfield & in the farfield), whereas photons don’t (at least not in the far field).
The elekton's E×H acts on elektrons, particularly on free electrons, in the wire.
The free electrons are moved, & the movement is resisted by the Cu.
The resistance ends up heating the Cu.
Every action has a reaction. Hence u would think that conductivity must affect the speed of electricity. In other words my elektons must be slowed moreso by bad conductors. This subject too must have kumup before. Praps they are slowed moreso. But praps that slowing is only say 1%, which would show, but would not show if u were not looking for it, or if u were ignoring it, or if it twernt important in the particular case under test.
For insulated wires, & on PCBs, there is a major slowing due to the insulation (insulation usually covers the whole surface), & due to the board material (in effect insulated on a half of the surface i think), hence a minor speed effect due to conductivity might not show up.
Such tests (speed of electricity) comparing metals & alloys etc would be simple -- have they ever been done? Still thinking.
Ooops. No. The speed of electricity should be slower the better the conductor.
A good conductor acts more strongly on elektons. A poor conductor (plastic) has so little action on elektons that the elektons will not jump onto its surface, to an elekton the plastic duznt exist (unless it is in the plastic insulation of a wire)(ie whilst the elekton is propagating/flowing along the wire).Elektons act on other elektons, hence the surface area of a wire has a saturation value, which depends on the conduction/resistance of the wire, & depends on the voltage of the source, & depends on the rate of production/supply of elektons. However, this interaction is a chicken & egg thing i suppose (as usual).
Here i need to remind myself that elekton elekticity is just one of the 3 kinds -- the others being (2) the movement of free electrons on the surface, & (3) the movement of free elektrons inside the wire.
Re that there saturation value – i wonder if it is affected by insulation. Praps knot. Still thinking.
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