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"Veritasium" (YT) - "The Big Misconception About Electricity" ?
Sredni:
--- Quote from: bdunham7 on January 01, 2022, 04:09:40 pm ---
Of course not and that is just another of your ridiculous straw men. The cable needs to dissipate the power associated with the required current and the cable's resistance. Somehow determining that by calculating Poynting vectors and an S-field would be the most ludicrously obtuse way that I can think of.
--- End quote ---
I didn't say you need to use Poynting. I said: if all you are interested in are voltages and current you can as well ignore where the power is flowing - in the space? in the cables? in the delta dimension between hyperspaces? who cares? - and just use V*I to compute your sock's power. You don't need to know the details of surface charge distribution on the surface of the conductors and resistors in your circuit to determine that the electric field inside is constant and follows the local form of Ohm's law, so that you can use voltages and currents in your circuit. But even if you choose to ignore that charge distribution because "it does not do anything for you", that does not make that charge disappear.
vad:
--- Quote from: Uttamattamakin on January 01, 2022, 06:24:56 pm ---Thanks I am the one who made this video.
--- End quote ---
Thank you professor for making this video, and deriving Coulomb's inverse square law (one of Maxwell's equations - the Gauss' law) from QED.
I have a question though. Consider the following experiment. Let's take a rubidium laser, shine its beam through a beam splitter, then one of the beams goes through a thick copper plate to a detector A, and another beam goes through the air unobscured directly to a detector B (sea level, 25C air temperature, 30% relative humidity). Can I assume that the probability of a photon reaching detector A (the one behind the metal plate) would be 999999 times higher than probability of reaching detector B, considering the same Coulomb's law and QED?
PS. Simplified version of this experiment can be reproduced by every member of this forum with a flashlight and a frying pan.
SandyCox:
--- Quote from: Sredni on January 02, 2022, 02:12:20 pm ---
--- Quote from: SandyCox on January 02, 2022, 09:45:36 am ---There’s nothing wrong with Maxwell’s equations. The problem is the misinterpretation of what the Poynting vector tells us. Here is what Haus and Melcher says in Section 11.3 of their book:
"we illustrate the danger of ascribing meaning to S evaluated at a point, rather than integrated over a closed surface."
--- End quote ---
--- Quote ---I attach the relevant pages from Haus and Melcher.
--- End quote ---
The full text is also online:
http://web.mit.edu/6.013_book/www/chapter11/11.3.html
--- Quote ---They use the standard Poynting vector S=ExH in Example 11.3.1. [snip]
Let's assume that the Poynting vector does indicate the path along which power is transferred. Then what is the mechanism that causes power to be transferred from the washer-shaped conductor to rod in this example?
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And what seems to be the problem?
The fact that you have lines going from a resistor to another resistor?
This is a kind of unusual geometry: we have a battery whose pole is directly connected to two resistors and then a perfect conductor shorting the other ends of these resistors.
Let's see if we can untangle the geometry and still see a problem. Consider this other example:
source: https://www2.oberlin.edu/physics/dstyer/CircuitSurveyor/help.html
--- Quote ---The problem is that humans misinterpret the meaning of the Poynting vector. It has no meaning without taking the integral over the surface of an enclosed volume.
--- End quote ---
Is the fact that the first resistor in the above figure is getting all the field lines coming from the battery what you find of concern?
--- End quote ---
Thank you for this example. It makes my point even clearer. According to the Poynting vector, energy is transferred from one resistor to the other. We know this isn’t what is happening. Energy is transferred from the source to each resistor and not from one resistor to the other!
SiliconWizard:
As rfeecs noted, a big chunk of the discussion is, in the end, really about a chicken-and-egg problem. So it can virtually go on forever. And Derek is a marketing genius. ;D
bsfeechannel:
--- Quote from: adx on January 02, 2022, 05:19:11 am ---If I grow wings and become capable of flight (and do fly), that isn't because of some cosmic permission granted by the author of a theory of flight.
--- End quote ---
You don't get it. There is a phenomenon that your dumbed-down understanding can't explain.
-- Here, take this theory, it explains it in clear terms what is going on.
-- Oh no, I'm an engineer, I cannot see the world except through my dumbed-down understanding. In fact, I'm going to declare that this phenomenon doesn't exist and who says that it does is wrong.
Give me break.
This kind of mindset is stupid. Especially in the case of engineers who are thought this bleep in their respective degrees.
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