- #36
berkeman
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This thread is now stickied because it is such a good debate about models and approaches to a real-world problem. Let's keep the debate technical -- I'm learning from it...
meBigGuy said:No, that is not true. You are thinking of the wavelength at the surface of the conductor where VF has meaning. That is what skin effect is about.
meBigGuy said:Avoiding confusion is the enemy of understanding. You have an incomplete (maybe incorrect) perception (visualization?) of skin depth and accept it because it avoids confusion? What is really confusing is unlearning the oversimplifications.
BTW, I am not an expert in this field, and will never be. But, neglecting that trivial factor (lol):
The wikipedia page has a drawing with current loops that shows eddy currents flowing in every which way inside a wire. How do those "backwards" current flows happen without being related to the wavelength of the signal within the medium? My tendency was to just look at that picture and just accept it, not thinking any deeper about what it meant and what must be true for it to happen.
Then look at the animation in the http://fermi.la.asu.edu/w9cf/skin/skin.html paper. You see the positive and negative field relationships with respect to the skin-depth. Again, try to visualize how you get reversed fields in such short distances.
The electromagnetics to produce those is just beautiful.
Sorry about the overlap and delay in my reply but I am at the far end of a chain of busy radio links. I also have work to do here that must get priority over PF.meBigGuy said:Baluncore:
Could you respond to my question in #40?
meBigGuy said:The thing I still don't get intuitively is Baluncore's statement "It takes time for a surface current flow to soak into a conductor because it sees it's own reflection. " I don't understand the source of this reflection. Is reflection the right word? Or, is there a better way to say this?
meBigGuy said:The thing I still don't get intuitively is Baluncore's statement "It takes time for a surface current flow to soak into a conductor because it sees it's own reflection. " I don't understand the source of this reflection. Is reflection the right word? Or, is there a better way to say this?
meBigGuy said:I'm still not quite getting it. The current density decreases continuously along the depth of the conductor. I'm trying to relate to that. That fits the description above: "(ironically) good conductors of electric current (charge) are poor conductors of 'electricity' (EM field energy) ". I can relate to the concept of reflection at the boundary, I just cannot associate the continuing decrease with reflection. But, perhaps the above is the key, not some sort of "continuous reflection".
sophiecentaur said:I see what you're getting at but I think you need to be careful here because the concept of 'poor conductivity' can imply energy loss and I think the evanescent fields are not totally in phase so little energy is actually lost. Compare the case of total internal reflection between two (ideal) dielectrics where the fields 'behind' the boundary actually carry no energy away from the surface. With a highly conductive metal, the skin effect phenomenon is at its strongest yet the actual loss is least.
Could it be an analogy too far?