Relationship between electrical continuity and flux resistance

[Scott S.]

I am wondering how these two are related...

If I take a steel base plate and touch a rod magnet to it, obviously that is a very low resistance to the flux and low electrical resistance

What if I raise the magnet by one inch, and then connect the plate and magnet with a 42 ga wire? Electrically this would read very low resistance, but it seems like the flux resistance would be high?

Or what about putting a sheet of paper on the plate, then setting the magnet on the paper?

What equations govern this?

[R.G.]

Electricity and magnetism are different. They do interact, but it's always a sideways interaction.

With electricity, you take a source of electrical pressure (like, say, a battery) and you can connect things between the + and - terminals and a current will flow, proportional to the resistance in the path between the + and - terminals.

With magnetism, you take a source of magnetic pressure - like a permanent magnet - and the magnetism flows from N to S (or S to N, depending on how you look at it).

This is where things start getting different. Everything "conducts" magnetic flux, even free space. There are no magnetic insulators, only varying degrees of magnetic "conductance". Iron is the best example of a magnetic field "conductor" and it conducts a magnetic field only about 20,000 times as well as a vacuum.

Iron happens to be an electrical conductor as well, but air, water, wood, hamburgers and anything else is also a magnetic conductor, just not as good as iron. Whether something conducts electricity depends on vastly different details than whether it conducts a magnetic field.

So to answer your questions:

If I take a steel base plate and touch a rod magnet to it, obviously that is a very low resistance to the flux and low electrical resistance

Yes. But it is only a coincidence. The M-field and E-field conductances are entirely separate things.

What if I raise the magnet by one inch, and then connect the plate and magnet with a 42 ga wire? Electrically this would read very low resistance, but it seems like the flux resistance would be high?

Yes, the electrical resistance is low and the M-field resistance is high-er. Copper is not any better at conducting an M-field than wooden sticks, so the M-field changes would be the same whether the copper was there or not.

Or what about putting a sheet of paper on the plate, then setting the magnet on the paper?

This electrically insulates the two, but leaves the M-field only a little changed. You could get exactly the same M-field by subbing in a sheet of copper as thick as the paper.

What I'm getting at is that M-field and electrical field conductances are completely separate.

[Scott S.]

I tried these experiments last night checked the gauss and its all correct.

Electrical flow seems easier to understand - the copper atoms have electrons and the electrons can move through the copper easliy (a great simplification).

I poked around on wikipedia, and it seems that magnetism relates a different atomic phenomenon. For the dipole magnet as in pickups, there is a magnetic moment that relates to number of electrons in the outer shell

http://en.wikipedia.org/wiki/Magnetism

http://en.wikipedia.org/wiki/Magnetic_dipole

The first article discusses that the magnetism caused by electron flow is governed by Maxwell's equations, that is what I guess I was remembering.

So, the atomic structure of a given material will determine the flux resistance (permeability), and although atomic structure also affects electrical resistance its two completely different phenomena.

I hope I have at least some of this right....

[David Schwab]

Also remember that any conductor around a magnetic field will have a current in it. Either by reluctance, as with pickups, caused by the strings, or eddy currents in metal parts, like base plates, covers, blades, etc.

[R.G.]

Also remember that any conductor around a magnetic field will have a current in it. Either by reluctance, as with pickups, caused by the strings, or eddy currents in metal parts, like base plates, covers, blades, etc.

This is only true if either the conductor and magnet are moving relative to one another, or the magnetic field is changing. A conductor sitting dead still in a non-changing magnetic field has no M-field-induced voltage across it.

It is also true that any conductor with a current flowing through it has a magnetic field going around it which is proportional to the current.

But for beginners, this info just confuses them if they're already confused about what conductance of electricity versus magnetic field is.