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Re: Sparks (and ions)

On Sun, 6 Sep 1998, Ed Schweber wrote:

Fair enough. But wouldn't the ultimate flow of charge through our bodies be
electrons migrating from atom to atom. Admittedly this is not a single
electron making the entire run from foot to finger, but is anything lost by
thinking of it as a single electron.

Hi again Ed! Nope, yours is a description of a wire. In electrolytic
conductors, charged atoms migrate and electrons do not. I think it's OK
to imagine that negative ions are carriers of electrons. But then I would
insist on describing the positive ions as CARRIERS OF PROTONS. Whenever
positive ions flow, the electric current is made of flowing excess
protons, protons which are missing the electrons which normally act to
"shield" them. This is very different than metal wires, where protons
(positive ions) do not participate in the electric current.

I realize that many educators will absolutely hate the term "excess
protons", since it implies that protons can be added to or subtracted from
atoms in order to give them a net electric charge. However, suppose that
a neutral atom has one electron and one proton. If I remove the electron,
then what is left? A positive ion remains, made from a single, bare
proton! Where hydrogen ions are concerned, there is no question that
protons can flow But what if instead the atom had ten protons and ten
electrons to begin with? If I remove one electron, then the result is a
positive ion having ONE EXCESS PROTON. All the other electrons and
protons electrically cancel, but one proton does not.

Some people believe that positive charge does not have an existence
independent from electrons, they believe that all positive charges
actually are "electron deficeit". While it's true that we usually create
an imbalance of positive charge by removing electrons, the resulting
positive charge actually takes the form of protons: protons which have
lost their adjacent electrons which had been cancelling them out.
Removing the electrons hasn't CREATED the positive charge, instead it has
exposed some postive particles which were already there within the
material.

You might want to check out these parts of my "electricity misconceptions"
page:

"ELECTRICITY" IS MADE OF ELECTRONS?
http://www.eskimo.com/~billb/miscon/eleca.html#made

WHICH WAY DOES THE "ELECTRICITY" REALLY FLOW?
http://www.eskimo.com/~billb/amateur/elecdir.html


>You're leaning in the right direction [in talking
>about induced charges]. Another way to say
>the same thing When you bring your
>surrounding E field and make it much stronger,
>and when the field is intense enough, a spark
>occurs.

But which is cause and which is effect. Is not the "compression" of the
electric field a result of the induction?

Yes, but don't they both occur simultaneously? Analogy: if I squeeze a
small balloon in my fist, is the rising air pressure within the balloon
caused by the tension in my hand, or is the tension in my hand caused by
the rising pressure? With the doorknob, maybe we could say that the
decreasing distance between the charged fingertip and the neutral metal
knob causes both the increasing induced surface charge AND the compressed
equipotential lines in the space between finger and knob.

>But the increasing force upon the "CHARGES" :)
> never grows strong enough to make them leap
>from your finger. Instead the electrostatic force
>applied to the air molecules causes the air to
>'ignite' and turn into plasma, which is a conductor

That's an interesting possibility that never occured to me. But will the
E field actually grow large enough to create a plasma.

Yes, that's what electrical breakdown is: when the field grows strong
enough that electron-avalanches start converting the gas into a weak
plasma.

Is it easier to pull
electrons from neutral oxygen and nitrogen molecules than it is to pull them
directly off a negatively charged finger?

Yes. Air undergoes electrical breakdown at, what, 15KV per cm? I don't
know the field strength required for field emission, but I know that it is
much, much higher. For example, a mechanical relay is useless for
voltages above a few hundred volts because the switch contacts will arc
across. But immerse the same relay in a hard vacuum, and it acts as a
high-voltage insulator when open. Vacuum relays are one type of
high-voltage relay. Add some sharp points, or crank the voltage way, way
up, and you will eventually get significant current from field emission.


Also, what would account for the light from the spark in the plasma
model? I had always assumed that the "jumping electrons" collided with the
H2 and N2, knocking their interior electrons electrons to a higher energy
level and that the light was emitted in the subsequent decay. In the plasma
model, I imagine that the free electrons would also emit EM radiation when
they reattach to the atoms molecules after the conditions to maintain the
plasma no longer exist. But this I suspect would involve primarily the
outermost electrons and I don't know if the resulting radiation would be
visible light.

Yep, I'm pretty sure that much of the light comes from flourescence of the
gas because of electron bombardment. Sparks give off a line spectrum, and
some of the lines are in the visual range. I don't know if the emission
frequency from the outermost electrons cause visible light. But because
the light is a line spectrum, there must be all sorts of energy levels
involved. If the spark temperature is high, there must also be a
continuous spectrum from the white-hot gas. I don't know if the major
portion of the light is from heating, or from the line spectrum.


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William J. Beaty SCIENCE HOBBYIST website
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