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| Veritasium "How Electricity Actually Works" |
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| electrodacus:
--- Quote from: hamster_nz on May 10, 2022, 03:35:09 am --- How is that momentum transferred? When a marble rolls past a stationary one, the stationary one doesn't just start moving. Do the charges have little sticks that the prod each other with? --- End quote --- They (electrons) have a charge thus they repel each other and so they do not collide. This electron wave moves very close to the speed of light no matter the voltage or current. So when an electron gets out of a source (battery, charged capacitor, any sort of generator) it will travel the loop (not that electron but the wave) at around the speed of light and so another electron will enter the source on the other side. It seems physicists think in terms of mathematical photons emitted and absorbed by the electrons but no matter the real mechanism for the electron wave it will travel in wire (metals have free electrons) unless there is sufficient energy (high voltage) to go through a dielectric (not the case with Derek's example). --- Quote from: hamster_nz on May 10, 2022, 03:35:09 am --- How does that current and potential get into the middle capacitor? And what what is current times potential, if it isn't energy? --- End quote --- As mentioned above electrons will repel other electrons (force will drop with distance) So this repulsion force works across a fairly large gap like the dielectric in a capacitor or even 1m in air. So electrons enters the left side of a capacitor that repels electrons from the right side plate of the same capacitor and the those electrons will travel (the electron wave it will not be the same exact electron) will get through wire to the plate of the second capacitor with will create the same effect on that second capacitor and then the third and so an electron will get back into the source. This energy is stored in all 3 capacitors (energy that got out of the source ends split between the 3 capacitors with some energy lost due to wire resistance). There is a big difference between energy being stored and energy being used to do work. So you can say that one single electron left the source and you end up with 3 electrons one in each capacitor. But the electron that left the source had much higher energy (source had higher voltage than the voltage across the 3 series capacitors combined). So knowing how many electrons you have is not a measure of how much energy you have. Energy as shown by the formula depends on the capacity in Farad (dependent on distance and plate area plus the dielectric) and the voltage squared. The higher the source voltage vs the voltage across the capacitors the higher the energy loss on the wire with alone should be enough evidence to show that energy travels through wire. A switch is a capacitor and yet you need to close the switch in order to transfer energy. If energy could flow through the capacitor witch that is what a switch is then you will never need to close the switch. Everything that is known point at the fact that energy travels through wires else switch could not stop the energy flow when open and there will be no loss as heat inside the wires exactly matching what will be expected based on amount of energy transferred and wire resistance to current flow. |
| bsfeechannel:
--- Quote from: Naej on May 09, 2022, 09:21:38 pm ---which explains clearly that it is a theory dictating where energy flows, not experiments. Much like bsfeechannel, they don't point to experiments, because they cannot. --- End quote --- It's theory explaining experiments. That's what a theory is for. I told you several pages ago that the idea that energy was transmitted in wires was already debunked in the 19th century based on experimental data. I even described what experiments they were. --- Quote from: Naej on May 10, 2022, 12:40:24 am ---Mmh I'm not quite sure why you renamed potential energy into 'backpack', but if I were to explain electricity to children, I would consider it. Is potential a forbidden word now? I'm curious how you see energy moving in vacuum. Is vacuum filling/emptying backpacks too? And giving to electrons/protons? --- End quote --- What is remarkable of Derek's experiment is that it tosses in the bin all the alternatives to the Poynting theorem--a kind of discussion that only entertain physicists--especially S=VJ, so cherished by the hydraulic analogy lovers. And when it comes to intuition, it seems that the Poynting theorem makes more sense now in the 21st century than it did way back when, as it can be stated by this underrated comment to Derek's video: |
| hamster_nz:
--- Quote from: electrodacus on May 10, 2022, 05:30:57 am ---As mentioned above electrons will repel other electrons (force will drop with distance) So this repulsion force works across a fairly large gap like the dielectric in a capacitor or even 1m in air. --- End quote --- If that is so, then that's a big problem. A circuit with a few very large capacitors there might be a Coulomb of charge 'in play'. For an given elementary charge, it has to be interacting with 6.24x10^18 other elementary charges in the circuit to find the overall force on it. That whole F = k Q1 * Q2 / d^2", summed up over all the charges. This is very unlike marbles rolling around on a flat surface, where marbles only exchange energy when in contact. But it gets worse. I might have a big bag of protons on the shelf, so they need to factor into the equation. Dave might have a really big bag of electrons under his desk in Australia, so that needs to be included. And then there are the rovers on Mars, waggling electrons around in their antenna. So that needs to be factored in too... the circuit may in fact be the receiver for the signals from Mars rover, so you can't say that those interactions don't matter and don't occur. If the true reality is based on charges interacting at a distance, then for any charge to know what is expected of it needs to interact with every elementary charge in the whole universe, and that means every charge knows all the others on a personal, first name basis - they are all sending each other little messages all the time. That would be truly amazing! Then an atom of Carbon 14 in a carbon film resistor resistor decays, that's two new elementary charges that every other elementary charge in your circuit and the while universe needs to interact with. It just never stops! If you are happy with that situation being how reality is, then by all means see the world as the sums of interactions of bulk quantity of elementary charges. It will be near enough in most cases. A few billion electrons here in this charge, another few billions over there. That is the lumped element model. So wires running next to each other are transmission lines are inductors and capacitors all the way along them. In that case, if electricity was gravity, you will be safe knowing that the apple will always fall towards the ground, and you can attribute it to the uncountable number of atoms in the apple are each individually being tugged on by the even more uncountable number of atoms in planet Earth, based on an inverse square law everybody learns at school - F = G m1 m2 / d^2 - which very similar to the equation for interacting charges. The presence of the electric field resolves all this false complexity. The charge interacts with the electric field locally. The field interacts with itself (like waves on a pond), combining and distributing information. The charge experiences all the interactions with other charges in the universe though their combined effect on the electric field exactly where it is. A charge doesn't need to communicate with Mars - that information is already there in the field. Those elementary charges can now stop writing their messages to all the other charges in the universe, and just go with the flow, directed by the electric field exactly where it is. And if something dramatic changes, like somebody connects a battery to a wire? That energy and information spreads out in the Electric field, causing charges in the wire to move until the field inside the wire is once again nearly flat (this is the "electron wave"), and all the 'potential difference' between the wires is the energy in the field between wires - there because of the battery. (once again this all ignore the magnetic field, which is actually needed to receive signals from Mars...) |
| PlainName:
--- Quote from: T3sl4co1l ---But it's not particularly important where and how it goes. --- End quote --- In principle I kind of agree with you, but I think it does matter in some cases. For instance, the recent discussion of PCB stackups is a bit of a nonsense until you take fields into account. |
| electrodacus:
--- Quote from: hamster_nz on May 10, 2022, 08:58:43 am --- --- Quote from: electrodacus on May 10, 2022, 05:30:57 am ---As mentioned above electrons will repel other electrons (force will drop with distance) So this repulsion force works across a fairly large gap like the dielectric in a capacitor or even 1m in air. --- End quote --- If that is so, then that's a big problem. ... (once again this all ignore the magnetic field, which is actually needed to receive signals from Mars...) --- End quote --- The lumped element circuit model for the transmission line works because it is what happens in real world. If calculations based on that will not provide accurate results then it will not be used. You maybe saw my Spice simulation for a 10m transmission line and the result is the same as what Derek got testing it in real world. When switch is closed energy will first need to charge the line capacitance and this is the reason you see a small current through the lamp as the lamp is a wire connecting the two capacitors in series. The question is not even as complicated as you make it to be and is just Does energy travels through wires in Derek's low voltage experiment ? The answer for me is a clear yes and nothing points to other conclusions as all measurements you make point to the fact that energy travels through wires. Energy is a generic term for all forms and you can transfer energy without wires but it will be in a different form like infrared photons that will be emitted by a transmission wire if resistance of that wire is not zero. An incandescent lamp filament is a wire with high resistance and it emits a lot of photons mostly in the infrared spectrum but as it gets hotter some in visible spectrum. And yes that is energy transferred outside the wire (those photons) but that is undesired for a transmission line so it is minimized so that most of the energy is transferred through the wire with as little loss as it will be economical. |
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