General > General Technical Chat
Why are physicists the electronics experts?
TimFox:
The relativistic velocity of the electrons is important to the design of the accelerator.
Berni:
GPS Satelites have to deal with the relativistic effects.
Firstly the atomic clocks up on the satellites run slightly fast due to being slightly out of earths gravity (also slightly slowed down due to going so fast, tho the effect is weaker so it looses out). But that is fixed by adjusting the trim on those clocks to match the ground clocks, not that it would matter since GPS would still work fine as long as all the clocks run slightly fast by the same amount.
The more observable effect of relativity is the fact that the GPS carrier signal varies by up to a few KHz due to the Doppler shift of the satellite moving towards or away. This relative frequency shift is measured by GPS receivers to get some extra information out of the signal on top of the usual CA code pseudorange measurement.
Rick Law:
--- Quote from: TimFox on August 23, 2020, 07:37:44 pm ---The relativistic velocity of the electrons is important to the design of the accelerator.
--- End quote ---
--- Quote from: Berni on August 23, 2020, 07:45:19 pm ---GPS Satelites have to deal with the relativistic effects.
...
--- End quote ---
Yeah, my initial reply there was poorly worded. My point was, the electronics are not at relativistic speed, so the electronics themselves don't have to deal with the effect of traveling at that speed.
Neither the linear accelerator itself nor the detection system itself is traveling. The xray (particle) is. The accelerator of course is designed with that in mind so it knows where the particle is as it accelerates the particle. But neither the accelerator nor detector themselves is traveling, the electronic components are stationary so they don't have to deal with relativistic effects on how the components work.
If the particle's energy level matters, then the particle's speed has to be factored in with energy calculation. Other than that, the application is rather like a lux-meter, absorb photon which is actually traveling at light speed and tell you how bright it is at the point, but the electronics themselves doesn't need to deal with any relativistic effect regarding itself traveling at relativistic speed because it isn't.
GPS: The electronics in the satellite are not traveling at relativistic speed, therefore the electronics doesn't have to deal with relativistic effect on its electronics due to traveling. The electronics themselves will work as well stationary or moving. However, the GPS application is one in timing, the timing calculation has to to deal with the time dilation.
Buriedcode:
--- Quote from: Connecteur on August 20, 2020, 05:25:36 pm ---When I look up the answer to an electronics question online, it's often a physicist who is giving the answer. Do they know more about electronics than someone who actually works with electronics?
--- End quote ---
Where exactly are you getting your "answer" from? Online is a big place - with thousands willing to answer questions regardless of any experience or qualifications, so ultimately you have no real confidence in the accuracy of their answer. Places like stackexchange and Quora are full of self-professed experts who can give wildly inaccurate answers with an air of arrogance - which really means nothing, they could be anyone.
It could be that the people who answer the most questions on the forums you ask, just so happen to be physicists who have retired, or you're asking the question on a forum/website that is frequented by physicists. Also, the title of the thread implies that the answers you got are from physicists who call themselves experts in electronics. Or did you just assume they were expects because they answered? It's another "lets post something controversial and see who bites" thread.
We've got three pages of replies, without a post from the OP.
TimFox:
The electron velocity is relativistic; x-ray photons, being massless, must travel at the speed of light. When setting up the accelerating cavities and excitations, one uses the relativistic velocity of the electrons as they gain energy.
When I took freshman Electricity and Magnetism, we used a wonderful textbook by Purcell. He introduced magnetic forces by showing that they resulted from relativistic effects on the motion of charged particles, even at the very low drift velocity of electrons in a conductor. That textbook (which cost less than $10 back in the '60s) is stored now, but I found this (curmudgeonly) discussion of Purcell's demonstration online:
http://physics.weber.edu/schroeder/mrr/MRRtalk.html
One of his complaints is how much that book costs now.
There is Special Relativity in the real world; General Relativity is less important to your day-to-day life.
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