Hi Jon:
I too would like to know the answer to this interesting question! I
always thought that electricity was the movement of charged particles
within an electric field. Let me elaborate.
A sealed vessel filled with air has atoms in it. These atoms have the
same number of electrons as protons. Under these circumstances, no
electric flow can exist. The electronic bonding forces are very strong,
but can be over come with enough energy. When an electron in the outer
orbit of an atom receives enough energy it can become a free electron
and if under the influence of an electric field it will be attracted in
a direction opposite to its own charge to an electrode or anode. It is
also free to move into the external circuit creating the electric
field.
The atom which has now lost an electron takes on a net positive charge
of one and it too can be influenced by the same electric field. It will
move in the opposite direction to that of the electrons moving towards
the cathode. Unlike electrons, these ions are too large to enter into
the external circuitry. So they are always present inside the vessel.
Under these circumstances, we see two kinds of electric current flow
electrons and ions. This is the theory I know from reading and study at
the university and talking to physicist friends at the Tektronix CRT
development labs.
Furthermore, what happens if we reduce the number of atoms inside a
vessel? It would only make sense to me that since there are fewer atoms
around there would be a reduction in the number of electrons and ions to
constitute an electric current.
A concept called "the mean free path" is often used in vacuum
laboratories to describe the hardness of a vacuum. In a closed vessel,
the average distance a particle can move without colliding with another
particle is the mean free path. The fewer particles available in a
closed vessel, the longer the mean free path. Pressure is also related
to the number of free atoms inside a vessel. Most vacuum tubes are
evacuated to 1 X 10^-3 TORR which is the pumping limit of mechanical
pumps. Add in series with the mechanical pump an oil or mercury
diffusion pump and you can get down to 1 X 10-7 or -8. Other
techniques, besides physical, exist to increase this hard vacuum. The
idea here is to chemically lock up atoms so that they are no longer free
to move inside their vessel. Gettering is the common method. A very
active metal is placed inside a physical carrier called a boat and not
allow to be open to its environment until the high vacuum is reached and
the vessel seal off. An RF induction heater then opens the boat and the
material (usually Barium) is splattered against the glass. If a free
particle comes in contact with the Barium, is then enters into chemical
bond with the active barium and stays there. This particle is no longer
free to move around to become a part of the electric current.
So if all of the particles were removed from a vessel, where do we find
the charged particles which constitute an electric current?
My conclusion is that no electric current exists if you don't have
particles! Be they electrons or ions.
Now if there is a new theory. It needs to be told because this is the
only one I know about which adequately explains electronic current
creation and flow.
If your friend wants to persuade you over to his point of view, then I
think he needs a new theory!
73's John
-------------------------------------------------------------------
Jon Ogden wrote:
>
> Hi all,
>
> I got a question. I had a discussion with a ham friend of mine on our
> way to Dayton this weekend. We were talking about the *gas* theories in
> tubes and tube arcing. His comment was that from his experience, he has
> determined that the voltage breakdown potential of a vacuum is LESS than
> that of the voltage breakdown potential in air. He said that while doing
> some EMC testing of a product he has designed for his company, he found
> this to be the case. He had to simulate lightning strikes at high
> altitude and thinner air. The breakdown potential was much less at
> higher altitude (thinner air) than at the thicker air of sea level. The
> arcs happened at less voltage at high altitude. So he has made the
> conclusion that if the breakdown potential of thin air is less than
> regular air, the breakdown potential of a vacuum is less still. I don't
> know if this jump can be made.
>
> Can someone help explain this? All my instincts tell me that a vacuum
> has the highest breakdown withstanding potential. I seem to remember
> hearing once though that thin air ionizes easier than "thick" air so
> perhaps that explains it.
>
> Thanks a lot.
>
> 73,
>
> Jon
> KE9NA
>
> --------------------------------------------------------------------------
> The Second Amendment is NOT about duck hunting!
>
> Jon Ogden
>
> jono@enteract.com
> www.qsl.net/ke9na
>
> "A life lived in fear is a life half lived."
>
> --
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--
Best 73's John
Amateur Radio K7JB -- Portland Oregon 97229
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