General > General Technical Chat
"Veritasium" (YT) - "The Big Misconception About Electricity" ?
SiliconWizard:
--- Quote from: bdunham7 on January 01, 2022, 10:25:29 pm ---QM, QED and QFT are non-intuitive and hard to grasp, but they certainly aren't a cute theory that fails.
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I was specifically talking about the cases in which it "failed" so far. Do not generalize what I said, which would tend towards a strawman argument. =)
--- Quote from: bdunham7 on January 01, 2022, 10:25:29 pm ---The fact that some of those QM results are difficult to observe directly doesn't invalidate or marginalize the theory in any way.
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If a theory does not survive observations, then it is, as long as it's the case, a cute theory. We have absolutely experimented and observed its applicability in various contexts. But in others, it remains unobservable (not sure this is a word?), so for those cases, it remains a cute theory. This doesn't marginalize it. It just means we fail to prove it's valid in some contexts. Whether it's worth considering it for those contexts even though it's impossible to observe is up to everyone's appreciation. It's like the string theory. In science, it's sometimes hard to know when you're wasting your time or when stubbornness will pay off, and it's always tempting to think we have just found the theory of "everything".
And now yes, as I also said, there are seemingly some recent advances - experiments with large molecules - which I agree sound promising, but again I would be prudent at this point. Time will tell though.
bdunham7:
--- Quote from: SiliconWizard on January 01, 2022, 10:51:24 pm ---I was specifically talking about the cases in which it "failed" so far. Do not generalize what I said, which would tend towards a strawman argument. =)
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I don't intentionally do the strawman and although reductio ad absurdum often looks like that, I haven't intentionally done that here either. Perhaps there is a misunderstanding somewhere, so can you cite an example where standard QM/QED has 'failed'? Or a situation or 'context' where it is not valid?
rfeecs:
--- Quote from: bdunham7 on January 01, 2022, 10:34:42 pm ---Perhaps you could read my post that I've linked and the one after it and then see whether you agree, disagree or don't understand my position on that. Can you have a static E-field without charges?
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I agree that moving the charge with tongs is creating an "energy flux". It can be thought of as P = VI. You will also create a magnetic field by moving that charge, so the Poynting theorem will give you the same answer. It has to. It is just math. I am content to consider it a mathematical result with no practical value for the DC case.
I agree that a static E-field requires charges to create the field. Let's say the E-field is created by separating charges and holding them in position. That required energy. You are saying the energy is in the charges instead of the field, or a combination of charge and field?
I agree that anything that changes that energy will require the movement of charges.
And yet, there is such a thing as "energy per unit volume" of an electrostatic field:
https://en.wikipedia.org/wiki/Electric_potential_energy#Energy_stored_in_an_electrostatic_field_distribution
bdunham7:
--- Quote from: rfeecs on January 01, 2022, 11:49:50 pm ---
--- Quote from: bdunham7 on January 01, 2022, 10:34:42 pm ---Perhaps you could read my post that I've linked and the one after it and then see whether you agree, disagree or don't understand my position on that. Can you have a static E-field without charges?
--- End quote ---
I agree that moving the charge with tongs is creating an "energy flux". It can be thought of as P = VI. You will also create a magnetic field by moving that charge, so the Poynting theorem will give you the same answer. It has to. It is just math. I am content to consider it a mathematical result with no practical value for the DC case.
I agree that a static E-field requires charges to create the field. Let's say the E-field is created by separating charges and holding them in position. That required energy. You are saying the energy is in the charges instead of the field, or a combination of charge and field?
I agree that anything that changes that energy will require the movement of charges.
And yet, there is such a thing as "energy per unit volume" of an electrostatic field:
https://en.wikipedia.org/wiki/Electric_potential_energy#Energy_stored_in_an_electrostatic_field_distribution
--- End quote ---
OK, it looks like we agree, 4 for 4. :phew:
IMO, the energy of a static field has to be considered as a the combined effect of charges and their fields. The energy per unit volume is an understandable and probably useful result of integral calculus, just like a lot of laws and observations (Faraday's Law, for example). But for the DC case, the relevant point is that the energy of the static field is invariant. Well almost, since waving electrons around with tongs will change the field a bit.
bsfeechannel:
--- Quote from: EEVblog on January 01, 2022, 09:12:31 am ---
--- Quote from: Sredni on January 01, 2022, 09:09:39 am ---
--- Quote from: EEVblog on January 01, 2022, 05:11:42 am ---I have not heard a compelling case of Poynting at DC that makes me think in any way that it's useful.
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Take your pick:
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Nope, still not telling me anything useful, just stating that's a way to look at it.
What can looking at it that way DO FOR ME?
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In the picture below, a DC is going through a solenoid. The magnetic field so generated is attracting a magnet that is moving at a constant speed due to friction. Clearly energy is coming from the solenoid and going to the magnet, which is being dissipated as heat.
But how do you explain that? Spooky action at a distance?
Could we have DC motors if energy weren't flowing already through the fields instead of the wires?
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