On Aug 13, 2007, at 8:18 PM, John Winterflood wrote:
Horace wrote:
<snip>
Suppose the DC power supply, a battery, carries a coulomb of
excess positive charge, or a coulomb of excess negative charge?
Charge can always be detected by the field that is around it -
provided you can get "around" it to measure! Gauss's law (I think
it is) says that if you construct a closed surface and then measure
the electric field all over that surface, then the sum (integral)
of that measurement tells you how much charge is enclosed within
that surface (fields are always measurable without needing to
connect a meter between two points - eg by a field-mill).
However if you can't get all around it, and the charge is arranged
so that the field in the areas where you can measure cancels to
some extent, then it is not (currently) possible to know that that
charge is present nearby. This is the situation within a charged
sphere (or Faraday cage) for instance. While ever you are confined
to the cage, you cannot tell from measurements that you can make
within the cage whether you and the cage are charged to a high or
low potential.
This is the manner in which potential is unmeasurable - you could
be surrounded by a layer of charge and at a very high potential,
but from within the canceling distribution that the charge occupies
on the external surface of the cage, you cannot measure what the
potential (or phi) is within the cage.
A similar case is true with gravity - you can't in principle tell
whether you are floating near to a lot of mass, or in empty space.
If you can make observations outside your enclosure - such as
looking at spectral lines from distant disturbances, and compare
them to the spectral lines from similar disturbances you can
create. Then it becomes possible to know the difference in
gravitational potential between where you are and the distant
observation - as time ticks at a different rate dependent on your
gravitational potential and the spectral lines will be shifted
accordingly.
So it is very likely that there is a similar test that could be
done to measure your electric potential - but in some way you will
have sampled the space outside of your cage by means of the signal
that has traveled from the remote location - through the space with
the field in it - to where you are.
I agree with the above. However, my objective, that which started
the conversation, is to design experiments with some degree of
control of and knowledge of surface (and immediate sub-surface,
within an atom or so) electron fugacity. The objective is to know if
a point on a surface in the experiment has more electrons than
positive charge by the potential it has, or at least to be able to
set the potential of that point to a value were it is clear as to
whether there are excess electrons there or not. My goal was not and
is not to measure absolute potential using a gauge established at
infinity or some other gauge remote from the experiment. The goal is
to be able to use potential as an indication of charge balance at
points within the experiment. My solution to this problem was to use
a grounded Faraday cage as a reference potential for the experiment
within it.
Assuming there is no excess of one charge type or another in the
universe it may be possible in some ideal sense to go far away from
the universe and use a neutral body there to establish a zero
potential, a reference potential. Provided you do not pass through
any Faraday cages, and you can measure potential relative to that
standard at infinity, for any given point P, you can then know by the
potential whether the close vicinity of that surface point P,
actually a volume (dx)^3, has excess charge. That is not my goal, to
use that neutral body potential for a gauge. However, I think by
that standard the potential of the surface of the earth is never
extremely high, in excess of a trillion volts say. This means the
inside of a good grounded Faraday cage, having only grounded
conductors inside (as a starting point), definitely will have for all
practical purposes all neutral matter in a low electron fugacity
state. I can say that with confidence because external fields and
excess charge are all cancelled out by movement of or removal of or
addition of charge on the cage surface. Since removal of even just
the free electrons in the first atomic layer of the cage would
require a field of over 10^11 volts, I can feel confident that the
inside of the grounded Faraday cage remains impervious to any
possible static Coulomb fields outside, and to the potential of that
Faraday cage's surface. The potential of ground inside the cage is a
good reference potential for that purpose. A highly negative surface
in the experiment in that frame of reference will necessarily have a
high electron fugacity.
On the other hand, if electron fugacity should prove important to
cold fusion at mundane voltages (a highly speculative hypothesis)
then cold fusion experiments of the past not done in a grounded
Faraday cage may have had experimental variability due to variations
in the atmospheric gradient and the local ground potential. The
presence of a passing cumulus cloud, for example, could significantly
raise the potential of an external field electrode or impose a strong
electrostatic field. Results with the Szpak cell cell show major
morphological changes to cathodes in even fairly minor fields imposed
by electrodes external to the cell (i.e. 6 kV across the whole cell,
including the cell walls which take most of the potential drop.)
Michel has said on an abstract basis that only relative potential
between plates matters with regard to charge balance, i.e. electron
fugacity. I don't think that is so. Unless the experiment is
enclosed in a grounded Faraday cage and potential is measured
relative to the cage it is not possible to know anything for sure
about electron fugacity, because of atmospheric fields and earth
surface charge. Within the cage a negative surface potential with
respect to the cage, especially if it is large, is in fact an
indication of high electron fugacity at that surface. Outside the
cage, relative potentials are not necessarily an indication of excess
charge of either kind.
At any rate, that is what I think. I hope I made sense.
Horace Heffner
http://www.mtaonline.net/~hheffner/
