Timeline for Electricity only flows in a complete circuit, so how does TDR (time domain reflectometery) work?
Current License: CC BY-SA 4.0
33 events
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| Nov 19, 2021 at 10:07 | comment | added | Paul_Pedant | @Peter-ReinstateMonica Thanks for that explanation. At my level of comprehension, 18th-century optics and quantum theory just replaces one form of magic by another, and further magic is surely yet to come. My take-away is that light sprays around a lot, but we only relate to the routes taken by the drops that get us "wet". Now I shall have nightmares about the waste of it all. Will somebody please turn off Betelgeuse -- nobody is watching right now! | |
| Nov 19, 2021 at 8:19 | comment | added | Peter - Reinstate Monica | @Paul_Pedant ... So the "path" of the light is all emergent behavior from entirely local interaction: The light does travel in all directions but we observe only the part that hit the denser medium at the specific place from where the emergent wave front propagated towards us. | |
| Nov 19, 2021 at 8:16 | comment | added | Peter - Reinstate Monica | @Paul_Pedant Late answer to your "light and denser medium" comment: I assume you mean "how does the light ray find the direction it needs to travel to match the prescribed refraction angle before it knows there will something be in the way?" That is "easily" explained: The "ray" is a misconception. Light is always a wavefront. Like water waves in a pool from a dropped pebble, light travels always in all directions; it does so from every point on the way (!). It is just that most paths cancel each other out through interference. What remains is the "path" we observe, also with refraction. | |
| May 29, 2021 at 19:29 | vote | accept | Jason | ||
| May 21, 2021 at 13:12 | comment | added | Paul_Pedant | @slebetman Completely agree with your points. But the OP laments that High School electrical course only deals with cases that require 18th Century theory. High School optics similarly only deals with theory of 200 years ago. | |
| May 21, 2021 at 9:19 | comment | added | slebetman | @Paul_Pedant Light still travels only in a straight line when it is gravitationally bent. It is space that is deformed. Think of how you would define a straight line on the surface of Earth - a straight line on Earth MUST be part of a circle. It is the same as space deformed by gravity - a straight line MUST follow the curvature of space. | |
| May 21, 2021 at 7:34 | comment | added | Frodyne | Here is another video that talks about return currents in greater detail: youtube.com/watch?v=icRzEZF3eZo - if you want you can skip to 8:05. | |
| May 21, 2021 at 7:15 | comment | added | Frodyne | This ( youtube.com/watch?v=ySuUZEjARPY ) is a video of a talk Rick Hartley held on "Proper Grounding in PCBs". In the video he starts off by talking about ground/earth and return paths. At around 19:20 he pretty much answers your question but I would recommend that you watch from at least 10:20 forward to get a better base to understand his point (or just watch the entire talk). | |
| May 20, 2021 at 20:03 | comment | added | Paul_Pedant | @Peter-ReinstateMonica For me, that's where it gets surreal -- Principle of Least Time (or Action). How does a photon know where to go before it even encounters a denser medium? A large part of me is in denial with modern physics, but the universe appears to continue to function without my consent, so I don't worry too much about it. | |
| May 20, 2021 at 16:20 | answer | added | Barry | timeline score: 0 | |
| May 20, 2021 at 10:45 | comment | added | Peter - Reinstate Monica | @Paul_Pedant Until you realize that the bent line is straight after all, in a sense. | |
| May 19, 2021 at 20:06 | answer | added | Phil Frost | timeline score: 9 | |
| May 19, 2021 at 7:37 | comment | added | Paul_Pedant | Compare with teaching Optics in high school. First rule: "Light travels in straight lines." Closely followed by prisms, mirrors, lenses, mirages, rainbows, bent sticks in water, and gravitational bending around black holes. Final rule: "Light travels in straight lines, except when it doesn't." | |
| May 18, 2021 at 22:17 | comment | added | Peter - Reinstate Monica | @WesleyLee If you are serious and exact most high school physics is entirely and fundamentally wrong. It somewhat depends on your definition of wrong (and a bit on your high school), but: All of classic kinetics is just based on the fundamental misconception of Newtonian immediate remote effect and Galilean transformations. And if you say "but it describes reality close enough" I answer "Ptolemaeus". | |
| May 18, 2021 at 17:55 | comment | added | BlueRaja - Danny Pflughoeft | Related: Does alternating current (AC) require a complete circuit? | |
| May 18, 2021 at 14:38 | comment | added | Wesley Lee | Most things taught in high school aren't exactly how they work. Just a close enough approximation. | |
| May 18, 2021 at 14:27 | answer | added | John Doty | timeline score: 1 | |
| May 18, 2021 at 12:43 | answer | added | pjc50 | timeline score: 5 | |
| May 18, 2021 at 12:00 | history | tweeted | twitter.com/StackElectronix/status/1394623837967470593 | ||
| May 18, 2021 at 11:53 | comment | added | Peter - Reinstate Monica | Also eternally relevant an old Radio Yerevan joke: Radio Yerevan was asked: "How does telegraphy work?" Radio Yerevan answered: "Imagine a large dog. The tail is in Moscow, the snout in Yerevan. When somebody pulls the tail in Moscow, it barks in Yerevan." "Thanks. Then how does wireless telegraphy work?" "Exactly the same way, just without the dog." There is probably more truth in it than the original author intended. | |
| May 18, 2021 at 11:49 | comment | added | Peter - Reinstate Monica | If you think about it: Not only can you send pulses through conductors and observe the reflection: You can even do that without any conductor! Imagine my surprise when during a hardware test of a TV receiver for a car I detached the antenna feeding the TV signal and still could watch the program! The air gap of half an inch transmitted enough of the signal to enable reception. | |
| May 18, 2021 at 10:38 | comment | added | user16324 | When you get to AC circuitry, capacitance and inductance, you will see that this IS a complete circuit involving the coax cable's inductance and capacitance up to the break. Thus it permits current flow ... just not DC current. | |
| S May 18, 2021 at 9:58 | history | suggested | Peter Mortensen | CC BY-SA 4.0 |
Copy edited (e.g. ref. <https://en.wiktionary.org/wiki/electricity#Noun>). Dressed the naked link.
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| May 18, 2021 at 9:31 | review | Suggested edits | |||
| S May 18, 2021 at 9:58 | |||||
| May 18, 2021 at 9:14 | history | became hot network question | |||
| May 18, 2021 at 6:32 | comment | added | wbeaty | Also, what does "electricity" really mean? "Electricity," is it a form of energy? But electrical energy always travels one-way, going from source to load (from dynamo to distant washing machines.) This "electricity" energy never flows in a circle. Even during AC, the energy goes in a single direction, source to load. So "Electricity" ...ISN'T a form of energy? Faraday would agree. JC Maxwell would too! In other words, Faraday and Maxwell would fail your high-school science test, because the test actually contradicts the physics they discovered. | |
| May 18, 2021 at 6:20 | comment | added | wbeaty | Imagine a device which cannot be explained by grade-school science books: a big wide capacitor with the terminals at one edge of the plates. If you discharge it, the whole thing can't discharge instantly. Instead, during fast discharge a WAVE goes at the speed of light across the plates. (Then the wave reaches the far edge of the plates, and bounces! It can bounce upon returning, bounce repeatedly, so during discharge, the capacitor rings like a bell.) TDR uses this "capacitor plate-wave" effect. | |
| May 18, 2021 at 2:19 | answer | added | AnalogKid | timeline score: 7 | |
| May 18, 2021 at 2:04 | answer | added | jwh20 | timeline score: 2 | |
| May 18, 2021 at 1:39 | answer | added | DKNguyen | timeline score: 22 | |
| May 18, 2021 at 1:32 | answer | added | nanofarad | timeline score: 37 | |
| May 18, 2021 at 1:20 | review | First posts | |||
| May 18, 2021 at 19:24 | |||||
| May 18, 2021 at 1:14 | history | asked | Jason | CC BY-SA 4.0 |