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| Sick of ridiculous KVL infighting |
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| Simon:
--- Quote from: instrumental on January 14, 2022, 02:35:06 pm ---Both sides are correct up to a point; then, one answer strongly dominates the other. It's a matter of knowing when certain approximations can be made and when those approximations no longer hold. --- End quote --- Bingo, so why are we still discussing it? in one sentence you have explained the actualy solution, both are right, both may be wrong, it's a matter of point of (technical and context) view. |
| instrumental:
--- Quote from: Simon on January 14, 2022, 02:46:17 pm --- --- Quote from: instrumental on January 14, 2022, 02:35:06 pm ---Both sides are correct up to a point; then, one answer strongly dominates the other. It's a matter of knowing when certain approximations can be made and when those approximations no longer hold. --- End quote --- Bingo, so why are we still discussing it? in one sentence you have explained the actualy solution, both are right, both may be wrong, it's a matter of point of (technical and context) view. --- End quote --- Well, if we agree about the solution after a few sentences, why are YouTube channels with millions of subscribers feuding about it? Partly it's just a kvetch about the way this topic is discussed. Partly it's speculating about how best to explain the problem. But this problem is important. My third-year instrumentation lecturer always liked to remind us that it was fields all the way down, and even at DC. He was a physicist at heart, and it showed; he was a wizard to us engineers. (Perhaps I'm biased this way -- spent a few years building AMR magnetometers, and miss the field, if you pardon the pun.) Carrying that mentality forward, I've seen things go wrong in industry because people ignore this -- if you forget about fields, you forget that you shouldn't route over splits in ground planes (or, really, split ground planes without rationale -- but that's a whole different religious argument). I worked on a receiver board for a LiDAR on an upcoming lunar mission and the receiver is borked for this reason (SPI bus routed over a GND split near the signal path) -- needs substantial, costly, time-consuming redesign and respin, complicated by the fact that the designer doesn't understand the issue and won't concede that it's a fields problem (despite every fingerprint being there, from qualitative EMC to being able to measure the SCLK signal rising edge on the TIA output). Forget about fields and you'll never be able to solve many of the noise issues you're dealing with -- and don't hold any hope for understanding why your boards have failed EMC. So, I put it to you -- are we educating new engineers right? Are we motivating the issues at hand well, and are we giving concise and intuitive explanations? If we're triggering holy wars then the explanations at hand are not good enough, and we need to do better. As to what those might look like? Well, I've no idea what's intuitive to newcomers of the field; I've been at this too long. What helps? How do we avoid more of the kind of 39-page inane fighting on this forum, and between YouTube electronics education superstars? |
| Berni:
--- Quote from: instrumental on January 14, 2022, 02:35:06 pm ---I'm not sure I agree with this. Both sides are correct up to a point; then, one answer strongly dominates the other. It's a matter of knowing when certain approximations can be made and when those approximations no longer hold. --- End quote --- What answer strongly dominates is again dependent on the context. Story 1: Someone is designing some sort of magnetic apparatus that involves pulsing a large electromagnet with some wires running around it, so perhaps the question is what is going to happen to those wires. In this case you model up your apparatus and run it all trough an EM field solver, find what sort of fields are going to be in there, what they do to that wire you care about....etc. Define your path along what you want to measure the voltage. We got the result we need and there we go. Maxwell all the way here. No use what so ever for any of Kirchhoffs stuff. Story 2: Someone is upgrading some sort of existing magnetic apparatus with a large pulsing electromagnet and has issues with wires that for some reason have to run near it. They don't have the CAD models of the thing since the thing was built by a company that shut down that branch of business 10 years ago, so doing an EM simulation would involve a good bit of caliper work to reverse engineer it and the costumer needs this thing working by the end of the week. So perhaps instead haul out that trusty old boatanchor network analyzer, hook it up to the electromagnet and the wire(keeping in mind that probing will be included in the measurement), measure the S parameters of it across the frequency range of interest. Fire up there favorite spice flavor and plonk it in as a transformer with those parameters. Now they can experiment with what circuitry they need to add around it to fix the problem they are having with the electromagnet interference. No Maxwell involved in any of this, it is all Kirchhoff paired with some AC circuit theory and numerical integration methods. No point in playing a fan boy of one or the other. All that matters is that you use the right tool for the job and at the same time understand the limitations of the tool. People often form opinions on there own needs and preferences, but just because something doesn't fit your needs or liking does not make it wrong, especially when that thing is actually the right tool to use for someone else, giving them excellent results. For this reason i find both explanations equally correct. But feel free to continue waging the Lewin vs KVL war on the forums, looks like there will always be someone up for discussion to try and convince towards one or the other side. EDIT: Btw i think Lewins KVL failiure demonstration is a great one. Really provokes some deep thought into what voltage actually is. This is exactly what the students need. Its just that the explanation of why KVL breaks here is a bit lackluster(He claims that KVL is simply wrong and does not work). |
| bdunham7:
--- Quote from: instrumental on January 14, 2022, 02:35:06 pm ---Both sides are correct up to a point; then, one answer strongly dominates the other. It's a matter of knowing when certain approximations can be made and when those approximations no longer hold. --- End quote --- I don't think that's true in the Lewin/KVL 'debate'. It's not like classical physics vs modern physics or anything like that. There's a stark disagreement over whether the voltage between two points in a given apparatus is a uniquely defined single number or can be different numbers depending on 'the path'. The debate devolves from there. |
| SiliconWizard:
And, Lewin's demonstration itself - oh I know, let's not get into that all over again - was flawed IMHO. Let's put another coin in the machine. ;D I think this guy makes a few good points, and exposes them in a calm and structured way: |
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