Re: IONS

["Ludwik Kowalski" <KowalskiL@Mail.Montclair.edu>]

Chuck Britton wrote:

> Chemists do a demo with a glass rod hooked up to 120 VAC.
> When the rod is heated to a dull glow with a torch, enough
> current flows to maintain the joule heating of the rod.

Like any piece of good information this begs for questions.
The first one has to do with a desire to reproduce the
experiment. How long and how wide is the rod? And how
is it "hooked" to wires leading to the socket of 120 V?

The second is more fundamental. Why does the dielectric
material become a conductor? I suppose that SiO2 are real
molecules, not associations of ions, as NaCl. What is the
dissociation energy of SiO2 and why do Si and O atoms
become ions? The "dull glow" temperature is about 500 C
and this corresponds to k*T=0.066 eV. The bounding energy
of molecules, and bounding energies of electrons (in neutral
separated atoms) are probably about 100 times larger.

The rate of cooling of the glass rod at 500 C is probably
large, perhaps 30 W. This would mean that to sustain the
constant temperature the electric current must be large.
More specifically, i=30/120=0.25 A and R=480 ohms. Very
small in comparison with perhaps 10^9 ohms, or more, at
room temperature. Perhaps the "glass" chemists use is not
pure. But how can it be; they are in the best position to
know.
                         Ludwik Kowalski