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Veritasium "How Electricity Actually Works"
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electrodacus:

--- Quote from: dunkemhigh on May 11, 2022, 03:37:13 pm ---
--- Quote from: electrodacus ---you will see that the conductor heats uniformly on the entire conductor cross section
--- End quote ---

Easy for you to say. How about you demonstrate that?

--- End quote ---

People tested that well before I was born it just seems that internet instead of being this great learning tool it becomes a space for misinformation.
What about you just measure the electrical resistance of a copper pipe with thin walls and the electrical resistance of a copper bar with same diameter then let me know if there is a difference.
If there is a difference in resistance that means electrons from your multimeter traveled through the middle of the copper bar not just close to the surface.
You will see that resistance will be proportional with the copper section area so electron wave will travel uniformly through the material.
TimFox:

--- Quote from: vad on May 11, 2022, 01:27:23 pm ---
--- Quote from: EEVblog on May 02, 2022, 05:43:26 am ---Hontas Farmer is back still saying the Derek is both right and wrong acording to QFT/QED

--- End quote ---

QED (as all other QFTs) is a perturbation theory that extends Classical Electrodynamics to a quantum scale. QED is by no means a more fundamental theory than Classical Electrodynamics, and as being the extension, QED cannot contradict Classical Electrodynamics at macroscopic level. https://arxiv.org/pdf/1201.5536.pdf

Because QED is the perturbation theory, its approximate mathematical framework quickly falls apart when trying to describe classical systems (systems with billions of photons, electrons), as discussed in this paper: http://old.cft.edu.pl/~birula/publ/ClassLimit.pdf

In other words, QED has it own domain, and Classical Electrodynamics has its own domain. These domains do not overlap. Within their respective domains each theory has been validated experimentally to a very high degree.

In other words, to describe energy transfer in macroscopic systems proposed in Veritasium experiments, the only scientific tool Physics has is Classical Electrodynamics, and it is accurate at given scales.

--- End quote ---

It is sometimes interesting to compare two historical processes: 
[1]  After Constantine adopted Christianity for the Roman Empire, he wanted it codified and there were a long series of Councils, including Nicaea and Chalcedon, to render the new religion in axiomatic form.
[2]  Many centuries later, when the new quantum theories arose, there was a time between the wars when leading scientists, including Bohr, Einstein, Schrödinger, Heisenberg and others, debated theory and experiment to found what became known as Quantum Mechanics.  One guiding concept was the "Correspondence Principle" that related quantum results at microscopic scale to classical results at macroscopic scale, initially disregarding special relativity.  That "principle" is now less firm than before (depending on the physical situation under discussion), but a good example of a (non-handwaving) quantitative expression of this relationship is the Ehrenfest Theorem (published in 1927).
Those conversant in mathematics can find a description thereof in the Wikipedia article:  https://en.wikipedia.org/wiki/Ehrenfest_theorem
vad:

--- Quote from: electrodacus on May 11, 2022, 03:18:41 pm ---
Energy flows inside the wire both for AC and DC

--- End quote ---

Not necessarily. Take a superconductive wire at DC Inside the superconductor, electric field is zero everywhere (electric field potential is the same at any point inside the superconductor).

In other words: E = 0 inside such wire.

Electromagnetic energy flow is described by Poynting vector:

S = E x H = 0 (if E is zero vector, then its cross product is also zero vector no matter H field strength).

So no, at DC electromagnetic energy does not flow inside a superconductive wire.

If you replace superconductor with a wire that has resistance, then there will be an electric field inside the wire along its axis (equal to wire’s voltage drop divided by the length of the wire).

There is also a magnetic filed inside the wire when it conducts DC current. It can be quantified by Maxwell’s 4th equation. Such magnetic field circulates around wire’s axis. It’s strength is zero at the axis, and increases to a maximum value at wire surface.

Therefore EM energy flow inside such wire will be non zero. However the direction of the flow inside the wire will be strictly perpendicular to the wire  (remember direction of E, and the fact that cross product of two vectors is perpendicular to the vectors being multiplied). The total flow at surface (surface integral S over surface of the wire) is equal to Joule heating of the wire.

Remaining EM energy flows outside the wire. Using Poynting vector formula and some math, it can be shown that the energy flown outside the wire + Joule heating is all the energy that flows out of battery. From conservation of energy principal, we can declare that there no other EM energy flows.
electrodacus:

--- Quote from: vad on May 11, 2022, 04:39:11 pm ---
--- Quote from: electrodacus on May 11, 2022, 03:18:41 pm ---
Energy flows inside the wire both for AC and DC

--- End quote ---

Not necessarily. Take a superconductive wire at DC Inside the superconductor, electric field is zero everywhere (electric field potential is the same at any point inside the superconductor).

In other words: E = 0 inside such wire.

Electromagnetic energy flow is described by Poynting vector:

S = E x H = 0 (if E is zero vector, then its cross product is also zero vector no matter H field strength).

So no, at DC electromagnetic energy does not flow inside a superconductive wire.

If you replace superconductor with a wire that has resistance, then there will be an electric field inside the wire along its axis (equal to wire’s voltage drop divided by the length of the wire).

There is also a magnetic filed inside the wire when it conducts DC current. It can be quantified by Maxwell’s 4th equation. Such magnetic field circulates around wire’s axis. It’s strength is zero at the axis, and increases to a maximum value at wire surface.

Therefore EM energy flow inside such wire will be non zero. However the direction of the flow inside the wire will be strictly perpendicular to the wire  (remember direction of E, and the fact that cross product of two vectors is perpendicular to the vectors being multiplied). The total flow at surface (surface integral S over surface of the wire) is equal to Joule heating of the wire.

Remaining EM energy flows outside the wire. Using Poynting vector formula and some math, it can be shown that the energy flown outside the wire + Joule heating is all the energy that flows out of battery. From conservation of energy principal, we can declare that there no other EM energy flows.

--- End quote ---


Wire is used as a medium to transport energy. If wire has resistance then part of the energy will be wasted in the wire so less of the energy will be available to your load. A wire with no resistance to electrical flow like a superconductor means that no energy is lost while traveling through the wire.

That energy that is delivered before electron wave had the time to travel the length of the wire is due capacitance between wires and the lamp just happened in that particular example to be in series with that cable capacitance so current charging that capacitor made by wires will also pass through lamp/resistor.

The transmission line model provides exact predictions of what happens in a real transmission line and the phenomena associated with that.
TimFox:
Of course, in vacuum, electron beams flow quite nicely.
In air, they flow less nicely in the form of arcs, sparks, and lightning.
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