Reboot: Is the "delayed Lenz effect" real or just a misunderstanding?

[tinman]

The experiment is performed every time anyone uses any of a slew of different electronic devices. Like a computer!  And under conditions that are far more precisely controlled than anything you or I can come up with on our benches.

Different _size and shape_ wires will have different _self inductances_ for a given length and/or resistance though. This may cause a detectable phase delay that you might be able to see on your scope at very fast settings.

Just try this. Set your function generator to make a triangle ramp waveform so you can tell precisely where the peaks are. (It's more accurate to use zero-crossings but easier to use peaks.)  Take two resistors of the same type and wattage rating but different resistances. Connect one end of each resistor to the output of the FG. (If your setup is normal, the scope and FG will share a common ground, so for this test you don't have to connect the FG's grounded output lead or the scope probe ground references. If your system is ground-isolated you should connect the black leads of the probes and the shield lead of the FG output together.) Make sure you have the same length of wiring for each resistor/probe combination, no other connection nodes, etc. Take your scope probes and set them both to 10x attenuation so you are using the builtin voltage divider in the probes, connect one probe to one resistor and the other probe to the other resistor. Start at a low frequency. Do you see any difference in where the peaks are of the two signals? Now start increasing the frequency. At the very highest frequencies my FG emits, between 3-4 MHz, I start to see some very slight phase difference between the two signals. At lower frequencies there is no phase difference. This dependence of the tiny phase difference on frequency indicates that this is an inductive effect, not a resistive one. The metal-film resistors I am using have slightly different inductances, which show up as tiny phase shifts in the measured peaks at high frequencies. On my equipment, using a well matched 1 ohm and a 10 ohm I don't even see any phase shift at the highest frequencies my FG will produce. Comparing the 1 ohm and a 100 ohm, I start to see some phase shift at the highest frequencies. Examining the resistors themselves, I see that the length of the metal film portion on the body of the 100R is almost twice as long as it is on the 1R, whereas the 1R and 10R have the same length of the resistive portion.

As MarkE has said, the speed of light, or current, in a material is set by the relative permittivity and permeability constants of the material. The time it takes for current to traverse a given length of material depends on those two constants, and the length of the material. For a given material making up a physical object like a resistor, resistance is often proportional to length! So a current "slowdown" in a resistive material can be due to the fact that the signal is travelling through a longer bit of material, rather than due to resistance as such.  But no resistor is only a resistor, it is also an inductor. No piece of wire is just a piece of wire, it is an inductor and a resistor both. So the results of signal phase tests show the effects of both.

TK,as you have no load on either resistor,you will only be measureing voltage,not current. The resistors must be under load to see if there is a delay between the current flow in either resistor.

[MarkE]

That is exactly what I wanted to point out next.
So the coil placed at the end of this elongated pole piece would exibit a delayed reaction to the EMF.
So Lenz reaction there is instant at the end of the core but only in reference to an already delayed EMF at that point.
All in all CEMF will be delayed as well from the point of view of the 'primary' coil.
So the 'delayed Lenz effect' is real and we just can not come to an agreement how to call it properly.

One needs to take "Lenz" out of the name because the time it takes a field to propagate has nothing to do with Lenz' Law.

I hope my reasoning is sound and well laid out in English (not my native language).

kEhYo

[MarkE]

TK,as you have no load on either resistor,you will only be measureing voltage,not current. The resistors must be under load to see if there is a delay between the current flow in either resistor.

If the hypothesis is that two different resistors of like construction but different resistances exhibit different propagation delays, then one will need large body resistors, very fast test instruments or both.  Due to the Christmas break I can probably get time on a friend of mine's equipment that goes into the GHz.  Do you have a specific situation in mind?

[kEhYo77]

One needs to take "Lenz" out of the name because the time it takes a field to propagate has nothing to do with Lenz' Law.

How do you propose to call this effect then? Make it short please.

[MarkE]

How do you propose to call this effect then? Make it short please.

It is: Induced magnetic field opposition.