Re: All that glisters is not gold

[brian whatcott <inet@INTELLISYS.NET>]

Tom gives me just the opening I need to correct a previous footnote
 on metal resistivity values.
(The strong alloy I was referring to earlier was of Al not Ag,
see below).

But to answer his question with all due humility, I note that resistive
differences are not principally assigned to differences in the number of
conduction electrons, but rather in their 'mobility'.
In this respect, it's helpful to tweak the iconoclasts who take pleasure
in reminding us that electrons do not travel down a wire at near the speed
 of light, (though energy usually does), about a statistical feature of
 electron motion, so to speak.

   Notwithstanding their strictures about the snail's pace of DRIFT
velocity - it is quite permissible to visualize electron velocity as
several million meters per second (electric field or no...)

   The model for resistance in metals is the probability that an electron
will collide with an ionic barrier. Ref 1 holds up nickel vs. nichrome
as an example of two materials with very similar numbers of conduction
electrons, but widely different resistivity (20:1)

He will understand I hope that this model description eschews explicit
reference to quantum effects about which I am unable to talk coherently
:-)

Brian

ref 1: EncBrit 15th Ed. "Solid State of Matter"

At 20:38 2/9/99 -0500, you wrote:
> In a similar vein, I have read that statistically, an atom of Ag has 1+
> electrons that are easily displaced by an external E-field, while Cu's value
> is more like 0.9 electrons.  How does this relate to resistivity?
> Tom McCarthy

 (corrigendum)
> > Some values for the pure materials:
> > Cu   1.7E-8 ohm.meters  (for comparison 70:30 brass abt 8E-8)
> > Ag   1.6E-8              incorrect! (strong alloy  5E-8)
> > Au   2.4E-8
> > Al   2.65E-8             corrected! (strong Al Alloy as high as 5E-8)

Cold working copper (into the HARD DRAWN form), provides a value of 1.77E-8
ohm.meter. The difference is ascribed to locked defects in the lattice.
brian whatcott <inet@intellisys.net>
Altus OK