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| "Veritasium" (YT) - "The Big Misconception About Electricity" ? |
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| Sredni:
--- Quote from: rfeecs on January 16, 2022, 08:14:12 pm --- --- Quote from: HuronKing on January 16, 2022, 02:57:43 am ---Yes, I'm aware of Feynman's explanation of radiation pressure - that's why I question the statements Naej is making in their interpretation of Carpenter. After all, Feynman remarks a moment later, --- Quote ---Therefore the force, the “pushing momentum,” that is delivered per second by the light, is equal to 1/c times the energy absorbed from the light per second! That is a general rule, since we did not say how strong the oscillator was, or whether some of the charges cancel out. In any circumstance where light is being absorbed, there is a pressure. The momentum that the light delivers is always equal to the energy that is absorbed, divided by c: ⟨F⟩=dW/dtc.(34.24) That light carries energy we already know. We now understand that it also carries momentum, and further, that the momentum carried is always 1/c times the energy. --- End quote --- --- End quote --- Carpenter denies there is any experimental evidence that light carries momentum: --- Quote ---The most obvious is momentum. The idea of electromagnetic radiation carrying with it a momentum, and hence exerting a force on any absorbing surface, epitomises the properties which are customarily taken as direct experimental evidence of the existence of the field. But, as is well recognised [4-9], these properties are unsupported by any evidence which is independent of the way in which they are defined. --- End quote --- I'm not buying it. I suppose he means that the way he defines things, it is charges acting on each other at a distance rather than fields acting on particles. This would require reformulating lots of physics since Maxwell. --- End quote --- I printed the paper but I haven't read it yet. Just skimmed through it and also to the letter at the end. Anyway, regarding the balance of momentum in a static system I have found interesting an example in Zangwill Application 15.3 "The hidden momentum of a static system" p. 521 You might find it interesting as well. |
| Naej:
--- Quote from: rfeecs on January 16, 2022, 08:14:12 pm --- --- Quote from: HuronKing on January 16, 2022, 02:57:43 am ---Yes, I'm aware of Feynman's explanation of radiation pressure - that's why I question the statements Naej is making in their interpretation of Carpenter. After all, Feynman remarks a moment later, --- Quote ---Therefore the force, the “pushing momentum,” that is delivered per second by the light, is equal to 1/c times the energy absorbed from the light per second! That is a general rule, since we did not say how strong the oscillator was, or whether some of the charges cancel out. In any circumstance where light is being absorbed, there is a pressure. The momentum that the light delivers is always equal to the energy that is absorbed, divided by c: ⟨F⟩=dW/dtc.(34.24) That light carries energy we already know. We now understand that it also carries momentum, and further, that the momentum carried is always 1/c times the energy. --- End quote --- --- End quote --- Carpenter denies there is any experimental evidence that light carries momentum: --- Quote ---The most obvious is momentum. The idea of electromagnetic radiation carrying with it a momentum, and hence exerting a force on any absorbing surface, epitomises the properties which are customarily taken as direct experimental evidence of the existence of the field. But, as is well recognised [4-9], these properties are unsupported by any evidence which is independent of the way in which they are defined. --- End quote --- I'm not buying it. I suppose he means that the way he defines things, it is charges acting on each other at a distance rather than fields acting on particles. This would require reformulating lots of physics since Maxwell. --- End quote --- Yes. He says momentum, which is just like energy, is just as arbitrary. You can observe a charge at point A accelerating a charge at point B but you can't tell from the experiment whether: - the charge A transferred momentum to the ether, which then transferred momentum to the charge B - the charge A lost momentum; the charge B gained momentum. Sredni: yes this can also be seen as the potential momentum of the charge, which is a far simpler computation. See equation 15 in https://physics.princeton.edu/~mcdonald/examples/thomson.pdf If you don't believe me that momentum is arbitrary, you can read the conclusion of Zangwill's 15.8.3 right after. |
| SiliconWizard:
Let's insert another coin. ;D Why is it that to illustrate the fact that the energy would flow "in fields" rather than "in wires" (again, whatever that really means), you have to resort to a transient phenomenon, and that you can't observe it at DC? Can you transfer energy from one wire to another distant (but unconnected to the first) one, at DC steady state? If you can't, why? =) And if you can, how close would the wires have to be? |
| adx:
--- Quote from: SiliconWizard on January 17, 2022, 12:41:02 am ---Let's insert another coin. ;D Why is it that to illustrate the fact that the energy would flow "in fields" rather than "in wires" (again, whatever that really means), you have to resort to a transient phenomenon, and that you can't observe it at DC? Can you transfer energy from one wire to another distant (but unconnected to the first) one, at DC steady state? If you can't, why? =) And if you can, how close would the wires have to be? --- End quote --- Me? Small coin, brief energy for now. Because: It is the nature of it. The wave solution is waves, and manifests as transient, even at DC. The transient phenomenon I drew attention to is pure, unadulterated, 100% DC except for the tiny end of the signal extending into space. If ignoring the mathematical fields, all the effect happens (at this end) over the scale of angstroms. I was hopefully careful enough to limit my description to in the transmission line so it can properly be called "DC". Sredni's post talks of a single electron (or "a charge") moving at constant velocity as essentially DC. Which it is. But it isn't at all when you think about it (it's a travelling Dirac pulse, the very antithesis of DC). So yes, you can transfer energy from one wire to another at DC steady state and it happens all the time. The field effect does not reduce with distance, that is an illusion caused by objects appearing smaller as they go further away in space(time), so there is no limit to the spacing. My point being that the "waves are strange" vs force times distance for charge carriers contexts are different. |
| SiliconWizard:
--- Quote from: adx on January 17, 2022, 02:47:45 am ---So yes, you can transfer energy from one wire to another at DC steady state and it happens all the time. --- End quote --- Can you show us? =) --- Quote from: adx on January 17, 2022, 02:47:45 am ---The field effect does not reduce with distance, that is an illusion caused by objects appearing smaller as they go further away in space(time), so there is no limit to the spacing. --- End quote --- That's quite fascinating. Can you show us? |
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