Does it? A pure resistance doesn't change its resistance value with frequency.If it is how you say "we know it does", kindly demonstrate it or link to an example please.

The skin effect can cause the effective resistance to increase with frequency. The highest current density is at the outer circumference of the conducting wire,and decreases as we near the center of that conducting wire. As we increase in frequency,the skin depth decreases,and so the effective resistance rises.

I have a feeling as to what your answer may be to this,and if you do answer as such,then i will explain as to how my claim of increasing resistance is valid to the question of a change in impedance.

Your question provoked me to think about modifying the impedance of a coil or transformer, so I tried to engage you to think about it too, hence the questions. I thought we'd explore the concept in tandem.

The reason i asked the question,is because there may be some simple way of checking to see if i can get the impedance to change. The question and investigation into this stems from MHs comment in relation to my last video. He seems to think that the drop in input power,and the increase in output power is the result in the change of impedance of the coil. As far as i am aware,everything that is needed in order for the impedance to change,is not there in the circuits operation. There is no change in the phase relationship of primary EMF and current,there is no change in frequency,there is no change in the output load(which is a pure resistive load)and there for there is no change in effective resistance or reactance.

This is the reason for the question,as from what i know,there can be no change in impedance if one or all of the above do not change. So i asked you in case you new of something else that can change the impedance of a coil.


Brad

The skin effect can cause the effective resistance to increase with frequency. The highest current density is at the outer circumference of the conducting wire,and decreases as we near the center of that conducting wire. As we increase in frequency,the skin depth decreases,and so the effective resistance rises.

Skin effect can certainly play into circuit currents, but since we are dealing with low frequency sine waves here, skin effect can largely be ignored in this case. Skin effect usually pertains to metalic conductors, and I am uncertain as to the effect in resistors themselves. I'll defer to PW on that as he may know the answer.

This is the reason for the question,as from what i know,there can be no change in impedance if one or all of the above do not change. So i asked you in case you new of something else that can change the impedance of a coil.


Brad

I'm willing to explore the possibilities of dynamic impedance changes, but at the moment can't see how it might be accomplished in a simple air core transformer, other than bringing ferromagnetic material near it.

Skin effect usually pertains to metalic conductors, and I am uncertain as to the effect in resistors themselves. I'll defer to PW on that as he may know the answer.

Skin effect can certainly play into circuit currents, but since we are dealing with low frequency sine waves here, skin effect can largely be ignored in this case.

The exact answer i thought you would post--and this is good.
We can now remove any change in effective resistance from the equation

I'm willing to explore the possibilities of dynamic impedance changes, but at the moment can't see how it might be accomplished in a simple air core transformer, other than bringing ferromagnetic material near it.

What would need to change if a ferromagnetic material was bought close to the air core transformer in order for the impedance to change--E.G,inductance?

Im not sure if you have seen my last video on the experiment,but maybe if you watch it,you will understand as to what it is i am referring to. You may relate this to another experiment,where we did not quite see eye to eye.

So in the video,i do test the difference in inductance with and without the magnet near the coil. I also place a large chunk of laminated steel core inside the air core cavity,so as i can get some sort of reference later on as to how much difference raising the inductance by a large amount makes on the P/in=P/out results. I think it is safe to say that the inductance increase is so small with the magnet in play,that it is not the cause of the effect.

Have a good hard think about it Poynt--about what drives the magnet oscillator,and how it could be possible to get the results shown. I will add that(although mentioned in the video),the input RMS value is kept at a constant throughout the test by the voltage regulation function of the FG--as can be seen in the scope shots below,where Ch1 is the voltage across the primary coil,and CH2 is the current flowing into the coil,measured by way of voltage drop across a 3 ohm CVR.

https://www.youtube.com/watch?v=mlb79xSh93w

Brad

Poynt, PW:

I suggest that you don't do anything yet with respect to Brad's question because it appears that Brad hasn't even done the work himself.  He believes his little experiment with the oscillating post that has a magnet on it, which is oscillating in front of a coil driven by the function generator, is showing "magical work coming from magnets" once again based on the two scope shots.  Now he is coming here asking for a spoon-feeding session and he is expecting, yet again, to see you guys do the work and validate his theory.  We all know how that one will end up.

Here is an earlier quote from Brad about his experiment:

Now,lets see your books and laws work that one out MH--and remember,this is a very simple setup that anyone can make,and verify my results-i think Mags already has--not sure on that though.

Your so happy to sit there and criticize my work--point out faults that don't exist ,dismiss PMs being able to do any work--then lets see your books explain the result's.

The P/in for each test-without and with the oscillating magnet are there in the scope shot's. Voltage and current is in phase--easy to calculate P/in.
P/out from the secondary is there in the video for both cases--so work it out MH-give ya books a good work over,and see what you come up with.
The change in inductance test was done in the video,and clearly shows that with the large laminated block increasing the inductance by a huge factor,still did not come close to the results of the oscillating magnet. So we can rule out any inductance increase. Then along with that fact,and there being no phase shift between voltage and current,or no change in frequency,and also the frequency being very low,and resistance staying the same,would take care of any sort of change in impedance or reactance.
So what else do your books have MH?

Well in fact in both of the scope shots there is a slight phase shift between the voltage and the current, and the two phase shifts are not the same.  That may or may not be significant in determining what is going on in the experiment.

I also explained to him that when he added the oscillating post and magnet to the system, the electro-mechanical impedance of the setup changed, and that's why he was getting different results.  From the quote above, he is saying that he disagrees that the impedance is changing.

So Brad adds the oscillating post and the current draw decreases and If I recall correctly there is also more power being dissipated in a five-ohm load resistor attached to the transformer secondary and the phase on the secondary voltage also changes.

I told Brad before he draws any conclusions to do a full power audit in both cases and see where the input power is going.  I also told him that he could use an optical system to understand the phase relationship between the oscillating post and the voltage from the function generator so he could understand what is going on there.

So at least it appears that Brad has done none of this.  All that he did was look at a kind of glorified "numbers in boxes" deal and arrive at a conclusion.

So there is no point in doing any kind of analysis for Brad until he actually tries to do the analysis himself first.

MileHigh

What would need to change if a ferromagnetic material was bought close to the air core transformer in order for the impedance to change--E.G,inductance?

One would think inductance, yes.

Have a good hard think about it Poynt--about what drives the magnet oscillator,and how it could be possible to get the results shown. I will add that(although mentioned in the video),the input RMS value is kept at a constant throughout the test by the voltage regulation function of the FG--as can be seen in the scope shots below,where Ch1 is the voltage across the primary coil,and CH2 is the current flowing into the coil,measured by way of voltage drop across a 3 ohm CVR.

https://www.youtube.com/watch?v=mlb79xSh93w

Brad

I did watch the video a couple of days ago.

An increase in impedance would certainly cause a drop of input current and possibly an increase in output.

What other introduced element can cause the circuit to appear as though the impedance has increased (i.e. a decrease in current)? How about an opposing voltage, i.e. cemf?

The input current is determined by the potential difference across the primary impedance, with the assumption that the opposite end of the primary is at gnd potential (see "normal case"). In this case Vpri is Vfg=3V. Now what happens if another FG is connected to the bottom of the primary? See "cemf case". Now Vpri is Vfg1-Vfg2=2V.

Nothing was changed in terms of the transformer impedance, but the input current is clearly going to be lower in the case when cemf is introduced.

Is this happening here and in the rotor example (pretty much the same in concept)? Is the moving magnet also causing a higher output? I don't know for certain, I'm just speculating at the moment in an attempt to explain the reduced input current without changing the impedance.

I choose my words carefully....I never stated that an inductor is a pure resistor. 


Please do not make the mistake of thinking that I am not informed of the difference between a pure resistor and a reactance, in this particular instance, an inductive reactance.


Regards

And please dont make the mistake that i referred to a pure resistance,as i clearly stated effective resistance.


Brad

So please do not do what MH dose,and add confusion by way of saying things are wrong by pointing out things that were never part of the question.

I have to laugh at that one considering the near-insanity with respect to Brad pointing out all sorts of things that were never part of the two wine glass questions and using that as a vehicle to play the "wrong" card on me.

Please cite an example or two of what you are referring to with respect to me Brad.

Bill:

The Budgie from Hell will haunt your dreams for the rest of your life:

https://www.youtube.com/watch?v=sH7XSX10QkM