On Jun 26, 2007, at 12:40 AM, Michel Jullian wrote:
Ah, you were counting on the "ground around", it makes sense now,
but then you must make sure there is some, e.g. your plate mustn't
be more than two or three times as wide as the gap distance and
mustn't cover the table entirely, otherwise the only ground your
emitter will see is the plate, or indeed you must use a ring or
something.
But anyway the slit plate experiment is better, it doesn't count on
the "ground around" and it works in steady state.
It's quite easy to measure a small DC current BTW, all you need is
a current to voltage amplifier which will let you measure tiny
currents to a virtual ground without an intervening resistor
(budget deflates ;-), see http://hyperphysics.phy-astr.gsu.edu/
hbase/electronic/opampvar2.html
It can be made inexpensively using a cheap FET input (near infinite
impedance) op amp such as the TL071. Use e.g. a 1 Meg resistor for
feedback, so you'll get -1mV per entering nA. You can protect the
virtual ground input against arcing by clamping it to actual ground
with two antiparallel diodes.
This is a nifty approach. I like it. It's similar to using a
voltmeter as a nano-ammeter. Have you done this?
The big problem, though, is still who wants to do the overall
experiment.
Also, I still think an AC signal might be useful for detecting
filaments, and maybe determining something about their size and
makeup. Their conductivity should be a lot higher than air or air
with drops, especially at lower frequencies. It would also be
important to measure the liquid flow rate.
Regards,
Horace Heffner
