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| Why are physicists the electronics experts? |
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| EEVblog:
--- Quote from: bsfeechannel on August 23, 2020, 12:34:54 am --- --- Quote from: EEVblog on August 22, 2020, 09:52:30 am --- --- Quote from: Berni on August 20, 2020, 06:32:14 pm --- This leads to things like the much debated topic around Dr. Lewin and Kirchhoffs circuit rules. --- End quote --- Yes, that was a absolutely classic case of the way an electronics engineer sees things, and how a physicist sees things. In essence both of them were "right". --- End quote --- Unfortunately, that's not true. --- End quote --- I used quote marks around the word "right" for a reason. |
| iteratee:
--- Quote from: bsfeechannel on August 23, 2020, 12:34:54 am --- --- Quote from: EEVblog on August 22, 2020, 09:52:30 am --- --- Quote from: Berni on August 20, 2020, 06:32:14 pm --- This leads to things like the much debated topic around Dr. Lewin and Kirchhoffs circuit rules. --- End quote --- Yes, that was a absolutely classic case of the way an electronics engineer sees things, and how a physicist sees things. In essence both of them were "right". --- End quote --- Unfortunately, that's not true. Tom Lee, that you interviewed on The Amp Hour Electronics Podcast, says the following in his book, Planar Microwave Engineering: A Practical Guide to Theory, Measurement, and Circuits, a book that every wannabe microwave engineer should read: As we noted early in this book, it is important to remember that conventional lumped circuit theory results from appproximating the way the universe behaves (in particular, from setting to zero some terms in Maxwell's equations [i.e. using special cases of those equations], effectively treating the speed of light as infinite). The much vaunted "laws" of Kirchhoff are not really laws at all; they are consequences of making simplifying approximations, and so they ultimately break down.² ² Failure to acknowledge this fact is the source of an infinite variety of false conundrums, many of which are debated ad nauseam on various internet chat sites ("proof that physics is broken" [or that engineers see things different than physicists] and that sort of thing, written by folks who are often wrong but never in doubt). --- End quote --- Erm is this not sort of obvious common-sense? I knew this prior to any study of electronics and zero physics education. I'd suspect anyone that's pondered this will have noted the issue. The manual distributed by S.I. IIRC explicitly disclaims that relativity is essentially ignored throughout. Meaning the basic definition of voltage as an instantanious measurement across space necessarily violates your light cone (duh). I recall this being explained rather dismissively as a niche detail applicible only to "specialized fields". Well it's pretty damn fundamental to everyday electronics. Any geek kid with hilarious gamer P.C. laced with fruit loopy LEDs has tweaked their memory timings, has intuition of phase velocity, and can tell you how many picoseconds apart their DRAM slots lie from CPU. |
| Rick Law:
Standard theory today is: if you are traveling with an electrical system (say, a PC on a space craft) at relativistic speed, everything should work just fine. If you are using wireless to send signal from your space craft off to something not traveling with you, that is where you will run into trouble -- apart from your getting out of range within milliseconds, the signal will be frequency-shifted. Another space craft traveling along side at similar speed should however receive the signals just fine. But, I can't think of anything we are doing where relativistic effect becomes significant... The fastest thing we ever made was the Juno probe. Back in 2016 when it was about to go into Jupiter orbit, with Jupiter's gravity helping, it was traveling at about 266,000 km/h (0.00025c). That was about 2.5x the speed we are orbiting the sun. At 0.00025c, relativistic effect is tiny rounding error. As to Kirchhoff's Law or issues regarding the simplification... Let me put it this way: What is the conductivity of an electron? That question doesn't even make sense. But it is a reminder of something we often forget: electricity (voltage/current) is a statistical emergent phenomenon - emerged from a flow of a large number of charged particles. Rather like heat/temperature emerging from random vibrations of molecules. As such, electronics and electrical rules applies only in the "normal world" where the statistical models were compiled and thus can apply. When you deal with statistics, there is no meaningful exact solutions. You only get probabilities. EDIT: The initial writing (above), I was trying not to be too direct. That risk offending people. But re-reading the post, I think I did not get the point across. So I am adding this few more direct statement. Hope I am not offending anyone. Don't fool yourself into thinking we can solve those problem analytically with exactness. Even today, we cannot solve Three-Body gravitational problems exactly. We do that with approximations. We cannot solve relativistic equations analytically with two black holes orbiting each other (when they get very close, there is where it counts), we have to solve it numerically. That didn't stop us from going to moon (moon + spacecraft + earth = 3 bodies), that we can't deal with orbiting black holes didn't stop us (LIGO) from detecting a black hole merger with gravitational waves. So there is nothing wrong with approximations. They are just fine. And as always, we need to apply solutions knowing the limitation, and all solutions are limited in domain(s). |
| TimFox:
A simple example of everyday things with relativistic features. Linear-accelerator x-ray sources (used for radiography and radiotherapy) achieve electron kinetic energies from 2 MeV up to over 20 MeV. The rest mass is 0.511 MeV. |
| Rick Law:
--- Quote from: TimFox on August 23, 2020, 07:11:33 pm ---A simple example of everyday things with relativistic features. Linear-accelerator x-ray sources (used for radiography and radiotherapy) achieve electron kinetic energies from 2 MeV up to over 20 MeV. The rest mass is 0.511 MeV. --- End quote --- But the electronic equipment themselves are not traveling. So we need not deal with the relativistic effects of electronic. The radiography detecting/capturing part of it will need to think about the relativistic effects to the extend necessary. Is it presence/absence or does the gradation of energy level matters? |
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