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Questions for those who know electromagnetism better than I do
Slartibartfast:
--- Quote from: gcewing on August 30, 2021, 12:54:28 pm ---
--- Quote from: Slartibartfast on August 27, 2021, 06:41:05 pm ---
--- Quote from: imo on August 25, 2021, 09:28:56 am ---My first lecture on "EM Field Theory" started with an intro given by the professor - "..do you really think the electrons transfer the energy from the power station to your household?
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An exceedingly silly rant, if it really happened. Of course the marching electrons (a.k.a. current) need the electric field (a.k.a.) voltage, to, as the multiplicative product, deliver the power.
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What he was probably getting at is that the power doesn't travel through the wires, it travels through the electromagnetic field surrounding the wires. See https://en.wikipedia.org/wiki/Poynting_vector
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Thanks for poynting out (pun intended) the obvious. ;D
But there is another dimension to this: Energy (and by derivation, power) is always the product of two properties of the configuration space. Electric current is only one, so there got to be another one (the field). More examples: In radiation it's electric field and magnetic field, in mechanics it's force and velocity. This is the origin of the intensity being the square of the amplitude, and thus the deeper reason of why we use 20 in the definition of dB, when it comes to amplitude but 10 when it comes to power.
Cheers Peter
emece67:
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m k:
Just a comment, nothing to do with anything in this thread.
I don't understad the direction of force when a photon interacts with an electron.
HuronKing:
--- Quote from: rstofer on August 20, 2021, 03:27:51 am ---You wind up dealing with Maxwell's Equations and NOBODY wants to go there voluntarily. Three people in history have understood Maxwell's Equations: Maxwell, Feynman and Einstein.
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I get your point in spirit but I'd add 1 name to that list - Oliver Heaviside. It never fails to astound me how he was able to not only re-express Maxwell's cumbersome notation in something much more elegant (and make MANY derivations and solutions of Maxwell's Eqs and coin terms we EEs still use without a second thought), but also reinvented (alongside Gibbs) how all of physics does its math.
HuronKing:
--- Quote from: Slartibartfast on August 27, 2021, 06:41:05 pm ---
--- Quote from: imo on August 25, 2021, 09:28:56 am ---My first lecture on "EM Field Theory" started with an intro given by the professor - "..do you really think the electrons transfer the energy from the power station to your household?? Have you ever seen an electron?? Electron is small and lightweight, almost nothing.. Moreover, the electrons travel a few centimeters in a second in a copper wire.. You would never have lit a lamp on your desk if it had worked that way.."
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An exceedingly silly rant, if it really happened. Of course the marching electrons (a.k.a. current) need the electric field (a.k.a.) voltage, to, as the multiplicative product, deliver the power. Makes you wonder, if the uphill bicyling professor cannot find out where his efforts go, surely not into the movement (a.k.a. velocity)? Completely analogous, the velocity needs the backwards pulling force, to, as the product, become the power sink that makes him pant.
I'd consider this a way to confuse students, a pedagogical desaster.
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What about reactive power and power factor? Complex power is, well, more complex than simply P = IV.
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