Magnet Myths and Misconceptions

[Pirate88179]

Bill,

I don't believe there is any physical change in the wire from extended use. Sounds like a myth if some are saying there is.

Thanks.  So, any change in the wire was due to external exposure to the elements and not any internal molecular change due to the movement/vibration of electrons.  Would this mean that the electrons move/vibrate in the empty space between the atoms that make up the copper and therefore have no effect on them?  Would it be like hitting a long pipe with a hammer and having the sound vibrations moving along the pipe from end to end?  I am having trouble visualizing this.  So then, the magnetic field surrounding a wire with moving/vibrating electrons is due to the electrons themselves aligning together to create the field and not the atoms of the copper conductor itself being manipulated in any way?  Then this would make the copper conductor an inert host to the activity of the electrons I suppose.

Now I find it harder to understand, if there is no interaction with the conductors atoms, then why do some materials act as conductors and some insulators?  If these vibrations occur in the empty space in the structure of the material then it should not matter what that material is, but we all know that it does.  Materials that make good conductors of electricity, as we all know, make good conductors of heat as well.  This would make me think that the molecular structure of the conductor material is important, but if the electron activity within the conductor has no interaction with the atoms of the material itself, then why would this be?

I just went through all of my electronics books over here where they discuss atomic structure, electrons, conductors and insulators, and I could not find any answer for this.

Thanks,

Bill

[poynt99]

Bill,

Metals are good conductors because they exhibit free (loosely bound) electrons in their structure. Insulators don't have free electrons, so they are poor conductors of electricity.

See this pdf and this Hyperphysics page.

Just because the free electrons in a wire are constantly scattered and colliding as they make their way from one end to the other, doesn't mean the wire becomes worn out. For the electrons that do leave the wire, there are an equal number entering.

[SeaMonkey]

I don't believe there is any physical change in the wire from extended use. Sounds like a myth if some are saying there is.

That's one I've not heard.

Although, it is reported that 'work hardened' copper is not
as conductive as freshly annealed soft copper.

[TinselKoala]

(snip)
TK:

There are a lot of misunderstandings about electric fields and charge also.  In a generator, there is no "charge" in the wires.  There is an induced electric field that pushes the electrons through the wires, without any net charge in the wires themselves.  Likewise, some people talk about voltage being related to charge density, but that's only for static electricity.  You have voltage in the windings of a generator with no excess charge density.  There are two sources of an electric field, the static electric field associated with electrostatics, and the "dynamic" electric field associated with changing magnetic fields.  A so-so analogy for current flow in a wire because of a dynamically induced electric field might be a simple vertical shaft with balls falling through a gravity field.  The gravity field is like the electric field and the balls are like the electrons.

(snip)
MileHigh

Ah... er.... um.... almost.
There is only one field, the EM field. It is the relationship between charge and motion.  There is no difference between a "static" electrical field as in "electrostatics" and the "dynamic"  electric field associated with changing magnetic fields. A generator does in fact separate charge and in a current-carrying wire, charge is indeed separated. Don't believe me? Connect a capacitor across the output of your DC generator and watch what happens.
The changing magnetic field in the generator produces a movement of charge. What happens in the wire that is distant from the changing fields in the generator? The charge pressure that is created by the generator "pushing" on local charges in the wire is transferred -- like charge repels like -- down the wire and at the distal end you see a voltage: charge pressure.
The main differences between "electrostatic" charge and "dynamic" charge (current) are the number of charges involved and whether they are moving or not. A Coulomb is a _huge_ amount of charge. Put a Coulomb of charge onto something where it will be retained and you will have huge electric field effects associated with it. Make that thing smaller and the charge density will increase: voltage increases: until it leaks off due to isolation breakdown and conduction. Put a Coulomb of charge through a conductor every second, and you have one Ampere of current flowing and a large magnetic field associated with it. Flow that current into a capacitor and watch the charge pressure accumulate (voltage on the cap rises). Same field, same pressure, same voltage phenomena, whether "electrostatic" or "dynamic".
You can have currents that consist of beams of electrons in free space, as in Cathode Ray tubes. You can have currents that are transferred by conductive plasmas of ions, as in neon tubes. You can even have currents transferred by large ions dissolved in fluids, as in electrophoresis. But in each case it is the _charge_ that is moved by external fields (which result in the charge pressure gradient, AKA potential, AKA tension, AKA voltage), and which drags whatever material carrier along with it.

[bboj]

And what is a charge?