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| Veritasium "How Electricity Actually Works" |
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| Sredni:
--- Quote from: TimFox on May 14, 2022, 04:25:09 pm ---Again, in that simple ideal circuit with a finite-value resistor connecting the second (initially uncharged) capacitor to the first (charged) capacitor, and no additional lossy elements (such as capacitor ESR or leakage) the total energy lost by the circuit itself (into heat) is independent of the resistance value, and my earlier statement holds, that it is the same value in the limit as R-->0. Of course, the time required to transfer the charge is directly proportional to that resistor value and the limit as R-->0 of transfer time (to a specific settling fractional value such as 1 ppm, or 14 time constants) is zero. Here, "limit" is the normal mathematical meaning of the term. --- End quote --- My biggest gripe with the R->0 limit is that it necessarily lead to an unphysical model. If charge needs to move from cap1 to cap 2 at a finite distance, the zero transfer time implies faster than light charge motion. Radiation takes you out of this untenable position: the charges move from here to there, but they need to accelerate and decelerate - hence there will be radiation. The two-cap problem is a model breaker. One way or the other, something's gotta give. |
| electrodacus:
--- Quote from: Sredni on May 15, 2022, 01:13:34 am --- My biggest gripe with the R->0 limit is that it necessarily lead to an unphysical model. If charge needs to move from cap1 to cap 2 at a finite distance, the zero transfer time implies faster than light charge motion. Radiation takes you out of this untenable position: the charges move from here to there, but they need to accelerate and decelerate - hence there will be radiation. The two-cap problem is a model breaker. One way or the other, something's gotta give. --- End quote --- Not sure I understand what you want to say. If resistance is zero you still have inductance both in connection between the capacitors and capacitor plates. So current and thus the time it will take charges to move from one capacitor to another will be limited. I do not see the problem with the two capacitors either with resistance or without. The first electric field in between the two capacitor plates on the discharged capacitor will only happen when the first electron gets to one of the plates and it will not be that electron that jumped first the space between the switch contacts when they got close enough but it will be caused by that forming a cascading wave traveling at the speed of light through wire. |
| vad:
--- Quote from: electrodacus on May 14, 2022, 09:17:08 pm --- So no energy is "radiated away" by in this case magnetic field as the electric field exists only between the capacitor plates but that also is not "radiated away" --- End quote --- Maybe in the world of trivial Spice simulations electric field exists only between capacitor’s plates, but not in the real world. A hint: add a second ideal inductor close to that ideal inductor that you mentioned and check if you can measure any voltage across terminals of the new inductor during oscillations. Then think about where does that voltage come from. The same question puzzled Michael Faraday about 191 years ago. He found the answer, and kids now learn the Faraday’s law in the 8th grade (well, at least in the country where I went to middle school half a century ago). Another hint (since you are a Spice fan): by the words “close” and “ideal” I mean coupling parameter’s value 1 in K statement. PS. Dave ought to add more educational videos to his channel. If people did not study electromagnetic induction in school, maybe Dave can close that gap too… |
| electrodacus:
--- Quote from: vad on May 15, 2022, 02:00:37 am ---Maybe in the world of trivial Spice simulations electric field exists only between capacitor’s plates, but not in the real world. A hint: add a second ideal inductor close to that ideal inductor that you mentioned and check if you can measure any voltage across terminals of the new inductor during oscillations. Then think about where does that voltage come from. The same question puzzled Michael Faraday about 191 years ago. He found the answer, and kids now learn the Faraday’s law in the 8th grade (well, at least in the country where I went to middle school half a century ago). Another hint (since you are a Spice fan): by the words “close” and “ideal” I mean coupling parameter’s value 1 in K statement. PS. Dave ought to add more educational videos to his channel. If people did not study electromagnetic induction in school, maybe Dave can close that gap too… --- End quote --- There will be a voltage drop across the inductor even if it had no resistance but the inductor has series resistance as parameter in spice and for the example with 47mH inductor that was set at 0.3Ohm. Capacitors and switch also have series resistance included in the simulation. I'm not a spice fan. Spice is just a tool that if used correctly will provide correct results. The spice simulations I showed get the same results as the experimental tests. There is a reason a transmission line in spice is simulated as a series of LC elements as that is the best approximation of what happens and it is confirmed by the results that are not in contradiction to experimental results including the one Derek made. |
| vad:
--- Quote from: electrodacus on May 15, 2022, 02:14:49 am --- There will be a voltage drop across the inductor even if it had no resistance but the inductor has series resistance as parameter in spice and for the example with 47mH inductor that was set at 0.3Ohm. Capacitors and switch also have series resistance included in the simulation. I'm not a spice fan. Spice is just a tool that if used correctly will provide correct results. The spice simulations I showed get the same results as the experimental tests. --- End quote --- I probably needed to express myself more clear. I asked you to create an ideal transformer by adding the second inductor. Anyway, you are wrong. Changing magnetic field of the inductor induces changing electric field that in its turn induces changing magnetic field, and so on. And all that radiates into the Universe at a speed of light… |
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