That said, even if we consider a perfect setup and a real discrepancy, my take here would be that KVL could still perfectly apply. We would just have to consider the loop having extra voltage sources from any induced voltage. That wouldn't defeat it, but make us consider that our circuit model is incomplete.
That said, even if we consider a perfect setup and a real discrepancy, my take here would be that KVL could still perfectly apply. We would just have to consider the loop having extra voltage sources from any induced voltage. That wouldn't defeat it, but make us consider that our circuit model is incomplete.
Simply put:
You don't get to pick and choose when you follow a law and when you don't.
This is physics, not politics~~
Tim
Not sure I got your point, nor that you got mine.
I've yet to agree with KVL not being met, until I get a consistent and formal proof of that.
Any electrical circuit made of physical, non-ideal components and non-zero length, non-zero impedance connections between them will get inductive and capacitive coupling with its surroundings. If you devise the real, physical circuit that it actually is...
physics is a domain where this is strictly prohibited.
I have a hard time believing that Lewin is "just trolling" or trying to get students to think as some have suggested, after reading his responses to Mehdi and others on his original video. I think this link will work, if not just look for ElectroBOOM's comment on the video, it should be near the top: https://goo.gl/JsKHb8.
If Lewin has a more subtle point he's trying to make, he's doing a good job of hiding it.
In electric engineering terms we say, it DOES matter how I twist or coil the leads of my voltmeter.
He'll do a video when he gets back from vacation in a week
In electric engineering terms we say, it DOES matter how I twist or coil the leads of my voltmeter.
In the real world it can (and in this case demonstrably does) matter how you twist or coil the leads. There is transformer coupling happening which is not shown on your theoretical circuit.
He'll do a video when he gets back from vacation in a week
As a relevant point of interest, you cannot have a half-turn transformer winding. It is always an integer number of turns. You have to connect the ends of your 'half turn' winding together somehow, for current to flow. Making the wire longer, as in including the test leads of a meter for example, does not alter the fact that the circuit still completes the same magnetic path as a complete turn would do. The longer wire intercepts a more diffuse magnetic field but over a longer distance, and the induced EMF is the same as if it were a tightly wound turn.
In the case of an induced emf the potentials in a circuit are no longer determined, they depend on the path and thus Kirchhoff's Loop Rule is not valid. Kirchhoff's Loop Rule is a special case of Faraday's Law (namely when phi/dt=0). Thus Faraday's Law is always valid.
For case 2 we say "in a variable field a voltage is induced in the voltmeter's leads", or "the leads act as voltage sources, too", or whatever, which is nothing more than (a wrong way of) saying that "the path DOES matter when moving charges in a variable (non-conservative) field".
If this were intentionally done to make his students think about the problem, his video would congratulate the student who figures out the omission/trick of how he produced this result
He even takes this argument so far to the point of saying that Kirchoff's voltage law does not apply to circuits with inductors, because they have a changing magnetic field:
http://web.mit.edu/8.02/www/Spring02/lectures/lecsup4-1.pdf
If you want to play this "path" game, and insist that voltage is not by default the lowest energy path between the two points, then you have to say that the voltage between those point is undefinable, no?
He even takes this argument so far to the point of saying that Kirchoff's voltage law does not apply to circuits with inductors, because they have a changing magnetic field:
http://web.mit.edu/8.02/www/Spring02/lectures/lecsup4-1.pdf
Thanks for the reference. This helps making it much clearer what he was meaning - especially on page 3.