EEVblog > The AmpHour Radio Show

#562 – Electroboom!

(1/194) > >>

bsfeechannel:
Dave, KVL doesn't hold under a varying magnetic field.

Repeat it until enlightened.

Mehdi now comes with yet another explanation for his lack (which he admits) of understanding of electromagnetism : the old vs new definition (i.e. what he thinks is the definition) of voltage.

As for Lewin's experiment, it was just Faraday's experiment with fancy test equipment. Faraday did what Lewin did, using an unshielded galvanometer with completely unshielded probes and using an electromagnet to generate the varying magnetic field.

If Lewin was wong in anything, Faraday was also wrong. And that's not the case for about the last two centuries.

So, give up this nonsense already. Please.

jesuscf:

--- Quote from: bsfeechannel on October 21, 2021, 03:16:01 pm ---Dave, KVL doesn't hold under a varying magnetic field.

--- End quote ---

Really?  So according to the statement, AC circuits (with transformers and such) can not be solved using KVL!  You better go tell the whole electric power industry that they have been analyzing circuits under the effects of magnetic fields incorrectly for the last 160 years!!!

bsfeechannel:

--- Quote from: jesuscf on November 03, 2021, 05:22:25 am ---
--- Quote from: bsfeechannel on October 21, 2021, 03:16:01 pm ---Dave, KVL doesn't hold under a varying magnetic field.

--- End quote ---

Really?

--- End quote ---

Really.


--- Quote ---So according to the statement, AC circuits (with transformers and such) can not be solved using KVL!
--- End quote ---

AC circuits can be solved with KVL as long as you maintain all the varying magnetic fields away from the path of the analyzed circuit. This is what happens with a transformer for instance. All the varying magnetic fields are inside the transformer core, not inside the path of the circuit.


--- Quote --- You better go tell the whole electric power industry that they have been analyzing circuits under the effects of magnetic fields incorrectly for the last 160 years!!!

--- End quote ---

I don't need to. The whole power electric industry never made the mistake of analyzing a circuit under a varying magnetic field using KVL. In fact the whole power electric industry started out because of Faraday's discoveries which was solely explained by Maxwell's equations. And that's what we use to this very day.

thinkfat:
I think Lewins model on which he applied KVL was incorrect. The lines in a circuit diagram don't interact with a magnetic field.

If you watch the original lecture, the error creeps in when he assumes "A1=A2" and "D1=D2", but this just doesn't hold.

bsfeechannel:

--- Quote from: thinkfat on November 05, 2021, 04:12:26 pm ---I think Lewins model on which he applied KVL was incorrect. The lines in a circuit diagram don't interact with a magnetic field.

If you watch the original lecture, the error creeps in when he assumes "A1=A2" and "D1=D2", but this just doesn't hold.

--- End quote ---

What is absolutely amusing about the people who can't accept that KVL doesn't hold under a varying magnetic field is the disparity of explanations.

For Mehdi at first, Lewin's experiment was flawed because of bad probing. When he tried to replicate the experiment and couldn't get a different result no matter how good probing he did, he tried to reinvent the theory creating what he calls the new definition of voltage.

Dave came with a Deus ex-machina called "Practical Engineering". It's a completely irrational explanation with absolutely no basis on science.

Cyriel Mabilde came with the "masked" EMF, which he states is much simpler to understand than the real thing which is Faraday's law.

Others tried to manipulate the math to make it appear that the voltages found in such a circuit actually add up to zero.

Now Lewin doesn't know how to apply Kirchhoff's law to a circuit, and, worse, doesn't know how to draw diagrams.

So summarizing, KVL always holds because Lewin didn't know how to probe the circuit, because he's adherent to the "old definition of voltage", because he's a physicist and not a practical engineer, because he doesn'1 know how to manipulate the math so that you make Maxwell's equation of magnetic inductance to always show a zero on one o the sides of the equal sign and finally because he doesn't understand how to model circuits and draw diagrams.

The truth is that "KVL always hold" is a myth, brilliantly debunked by Lewin. And up to this day no one could show that those two resistors in a loop under a varying magnetic field will not show different voltages, no matter what.

You can fool an audience. But, as Richard Feynman said, nature cannot be fooled.

Navigation

[0] Message Index

[#] Next page