Inductor Polarity??

[Mark Tillotson]

As normally occurs that the capacitance of the coupling cap is several order of magnitude larger than the stray capacitance, the cap shorts both ends at the frequencies in which strays are relevant.

Its caps in analog filter circuits than matter most, as one end is usually driven at low impedance (output of opamp) and the other is at a high impedance junction with other R's and C's and opamp inputs - you want the outer film at the low impedance end where those nA's can flow away without affecting the voltage much.

 

[Mark Tillotson]

The figure below shows what I meant, though you might think it's trivial.
Electrons stay at the inner film have higher potential to each other. They have a tendency to travel to the outer film.

No, no charges flow between the films (that's the point of a capacitor), equal and opposite charges accumulate on each side of the dielectric establishing the electric field across the dielectric - but none of this is relevant to stray capacitance of the outside of the component to the surrounds, this happens whether the component is a capacitor, inductor, resistor, battery, or whatever.


The electric field strength is directly related to the areal charge density on the surface of a conductor. In the curved geometry of a cylindrically rolled capacitor this means the charge density will differ between the films slightly as in the diagram, but so too does the field strength due to the field lines concentrating closer to the centre, and everything is stable - the total charge is zero as one film has +ve charges and the other -ve charges.


Note that for metal conductors a +ve charge corresponds to a missing electron, leaving a metal nucleus's charge unbalanced.

 

[DF96]

The figure below shows what I meant, though you might think it's trivial.
Electrons stay at the inner film have higher potential to each other. They have a tendency to travel to the outer film.

You forget that an absence of free electrons behaves in exactly the same way as an excess of free electrons. Hence capacitor leakage does not depend on polarity.

 

[DBruce]

You forget that an absence of free electrons behaves in exactly the same way as an excess of free electrons. Hence capacitor leakage does not depend on polarity.

I am not sure if I read the above correctly. As I have said, the current in copper is carried by free electrons, not electron-holes.

Only electrons can move in copper, and if there is any leakage path, only electrons can travel through it. So if electrons are put at the outer film (more negative side), it would be harder for them to travel through the leakage path (from the outer to the inner) than in reverse, because there is an extra potential difference to overcome.

Edit & add:

Imagine this, two free electrons find a leakage path and travel through it, during their journey to the inner side they find that they are getting closer to each other, but they hate each other...

 

[DBruce]

No, no charges flow between the films (that's the point of a capacitor),

I am talking about the leakage current.

 

[Mark Tillotson]

BTW any leakage in films capacitors is normally extremely small, picoamps.


Any leakage is through the dielectric, and it will be carried by whatever charge carriers can travel through the insulator, be it electron, hole or proton - yes protons (hydrogen nucleii) are mobile in many materials(*). At the interface with the metal plates electrochemical reactions will occur if necessary to convert flow to electron flow in the metal.

Insulators and semiconductors can support electron-hole pairs (there's no sharp distinction between semiconductor and insulator, its a matter of degree and temperature). Diamond is an insulator at room temperature, a semiconductor when heated.

(*) protons are charge carriers in water, and presumably many hydrated materials like wood, for instance. The ability of protons to hop from water molecule to molecule is what makes moisture the enemy of static electricity, as in humid conditions most materials support a surface scattering of adsorbed water molecules.

Protons hop from one water molecule to another given suitable energy conditions

 

[DF96]

Imagine this, two free electrons find a leakage path and travel through it, during their journey to the inner side they find that they are getting closer to each other, but they hate each other...

If you are correct then not only would leakage be polarised in film caps, but also an isolated film cap would eventually develop a voltage across it as the electrons try to migrate to the outer foil. I have not heard of such phenomena.

Anyway, you are asserting this new idea. Please make it concrete by estimating the size of the effect. Then we can judge whether it has any relevance to real circuits.

 

[DBruce]

If distance between electrons are changed, the potential is changed.

What is the value of electrostatic potential energy of two electrons separated by 3 angstrom in a vacuum? - Quora

What is the size of the effect? I have no idea!
Since it's only small leakage in the film capacitors, but it's Amps in spiral inductors, I would assume the inductor polarity is more audible to us. And if people are telling the truth when they say that they can hear the difference when crossover inductor polarity is swapped, then...

 

[DF96]

OK, no attempt at serious defence of your idea, just the usual audiophile woffle.

 

[Osvaldo de Banfield]

Why not to return to the original inductor thread, or it has already converted in another cap thread, and there are dozens of this.