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On 08/22/2003 12:02 PM, Vern Lindberg wrote:
>> What is the conductivity of the water used?
An excellent question.
>> Unless it is high purity
>> it may be acting more like a conductor than an insulator, and the
>> capacitance determined by the gaps between water and plate.
Quite so.
On 08/22/2003 12:31 PM, Wolfgang Rueckner wrote:
>
> I find no difference in the results between distilled and regular tap
> water.
That doesn't dismiss Vern's question ... in fact
that's a dead give-away that you're being swamped
by conductivity in both cases!
Remember that even the purest water contains
nontrivial amounts of OH- and H3O+ ... namely
a 0.1 micromolar concentration of each.
The conductivity of the purest water is
distinctly nonzero. Answering Vern's question
in my head I get an RC time constant of
something like 150 microseconds, so if you do
the experiment at 1kHz or below you're asking
for trouble, no matter how pure the water is.
I strongly recommend you answer Vern's question
before proceeding.
Huge hint:
http://www.google.com/search?q=electrical-conductivity+ultrapure-water+ohm+OR+ohms
Another hint:
timeconstant = R C = (R*length) (C/length)