General > General Technical Chat

Veritasium "How Electricity Actually Works"

<< < (83/185) > >>

IanB:

--- Quote from: electrodacus on May 11, 2022, 06:55:56 pm ---You have a wrong understanding of what energy is and how it is transferred from source(battery) to load (lamp/resistor).
--- End quote ---

If on the one side we have electrodacus, who is right, and on the other side we have the rest of the world, who are wrong, then really all rational people would wish to be with the rest of the world and remain wrong. Apparently, in this scenario, being wrong is the right place to be.

electrodacus:

--- Quote from: vad on May 11, 2022, 07:13:42 pm ---
You are using wrong tools. Spice by no means can be used to simulate electromagnetic field in matter and space.

Also, at DC, you did not have to go that far by drawing what looks like a transmission line. 3 resistors (one for load and two for each wire), a battery and a ground symbol are sufficient for DC analysis in Spice.

--- End quote ---

That transient when you are closing the switch (with is what Derek concentrated on) is not DC.
All that was needed and if you understood the graphs is exactly what Derek got as a result just wrongly explained the reason for that result.

electrodacus:

--- Quote from: IanB on May 11, 2022, 07:18:57 pm ---If on the one side we have electrodacus, who is right, and on the other side we have the rest of the world, who are wrong, then really all rational people would wish to be with the rest of the world and remain wrong. Apparently, in this scenario, being wrong is the right place to be.

--- End quote ---

It is very clearly most engineers understand as well as I do how things work so are most Physicists.
There is no evidence against what I'm saying and no evidence for the claim that "energy doesn't flow in wires"
It is not the first time when Derek shows his inability to understand energy and energy conservation.

Way waste resources to do the transmission line experiment when we know (some of us) how to simulate that.
I got the exact same result from stimulating a transmission line as it is much easier to take measurements there including integrating power to get energy at different points.
So is not as you think me against the world it is me doing my best to educate you.

ejeffrey:

--- Quote from: EEVblog on May 11, 2022, 11:03:52 am ---
--- Quote from: dunkemhigh on May 11, 2022, 10:40:49 am ---I think that's missing an important thing. No doubt we are all mostly agreed that there is some fields stuff going on before the wires are connected, but what it's really about is after that, when there is a solid wired connection. Does the energy flow in the wire, on the wire (skin) or is the wire merely a guide and the energy actually flows still in the field? As I see it, and it's sometimes tricky to remember what the argument is about, it's that last option which is the crux of the video and this discussion.

--- End quote ---

For me the question is entirely about DC and energy inside vs outside the wire. Nothing to do with switches, transmission lines, capacitors, inductors, transformer theory, antenna theory etc etc.

--- End quote ---

For steady currents you can calculate energy density (ignoring prefactors and constants of nature) as qV + I*Phi [Phi == magnetic flux]. or E^2+B^2 and you will get the same answer.  The former describes the electric energy in terms of charges, the latter in terms of fields.  You can't really get away from describing the magnetic component in terms of some field in free space because there is no scalar magnetic potential, so I have picked a form where the current plays a role, but I don't need to refer to equivalent circuit elements like L.

Taking only the electric component qV, that is zero on the interior of a conductor because the net charge density is zero.  There is a small electric field inside the wire to overcome the wire resistance but the net charge density is zero.  The only place with a net charge density is the surface of the wire, and in the charge model that is where all the electrostatic energy is stored.  Even though the current is uniformly distributed across the wire cross section there is no (electrostatic) energy density there.

The magnetic component is harder to nail down.  For the field centric approach it's no problem: B is unambiguously defined everywhere, so we can just integrate up B^2.  But the flux * Phi representation is sort of inherently non-local: its is the current around a loop times the magnetic flux through the loop, so a product of quantities measured at two different locations.

So at DC, you can consistently define the electric component of the energy density to the wire *surface* as an alternative to the fields.  When you include the magnetic component or deal with AC or transient behavior you pretty much have to fall back to a field based approach to energy density.  There is no reasonable way to quantitatively define the energy to be stored in the volume of the wires. 

vad:

--- Quote from: electrodacus on May 11, 2022, 07:21:41 pm ---
That transient when you are closing the switch (with is what Derek concentrated on) is not DC.
All that was needed and if you understood the graphs is exactly what Derek got as a result just wrongly explained the reason for that result.

--- End quote ---
I thought you were referring to DC when you wrote this: “ The difference is that with DC the energy flow is uniform inside the wire meaning the entire section of the wire is used while with AC the higher the frequency and line capacitance the more charges will flow closer to the surface forming the capacitor.”

No matter DC, AC or transient analysis - you are using wrong tools.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod