The Romer-Lewin ring with inductors (part 4a) - Scope measurements step by step
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- Опубліковано 22 сер 2024
- This is ridiculous. I cannot even join two two minutes videos! I have to split part 4 in three or four parts.
This video shows all voltages on the scope: the exciting 20 Vpp voltage, the EMF of a single turn, and the voltages along the opposite branches of the ring.
While looking at the scope screen with all three signals present with the same phase, some of you might be tempted to draw the conclusion that KVL still works since the purple signal (the EMF of a single turn) equals the sum of the yellow signal ( the voltage across the half ring with the small inductor, taken with inverted polarity) and the blue signal (the voltage across the half ring with the large inductor).
That would be an incorrect conclusion, since when traversing the ring there is no place where the EMF can be located: all we have is two half rings with two voltages that do not add to zero: KVL fails!
The sum VH + (-VL) = EMF is Faraday's law.
Note:
Clearly, I am not the first to have used a toroidal transformer to demonstrate non- uniqueness of voltage. The father of all toroidal transformer experiments (with resistors) is this one, from the MIT OCW
• Chapter 10.0.1: Non Un...
It is featured in the textbook by Haus and Melcher, "Electromagnetic fields and energy" (chapter 10, page 2), and also in Zahn's "Electromagnetic field theory - A problem solving approach" (paragraph 6.2.3 "Transformer Action").
Both books are freely downloadable on the MIT OCW website.
The toroidal experiment is also featured in Purcell's EM textbook, as an exercise: (ex. 7.4, solved on p. 710 in the third edition).