Contrary to our hope an increase in d.o.p. did not result in the
elimination of irreproducibility. Sign reversals occur without
any obvious patterns at all voltages. What is going on?
To answer this question we decided to simplify the dissectible
capacitor. Instead of working with three surfaces (AL-Lexan,
Lexan-Lexan and Lexan-AL) we decided to focus on a single surface.
The piece of lexan was coated with a conducting layer (carbon) on
one side and placed between Al blocks for one minutes at 1000V.
Then AL blocks were discharged, as usual, and lexan was placed
into the Faraday cup. The net Q was found to be zero. We repeated
the same at 2000 and 5000 V and each time Q was zero. The result
did not depend on which side of lexan (coated with C or not-coated)
was in contact with the grounded Al block.
The next natural thing was to use two identically coated lexan
sheets. We placed them into the dissectible capacitor (carbon layers
toward Al blocks) and exposed to 5000 V for one minute. We were
nearly sure that Q will be zero; we already knew that each half
shows Q=0 when exposed separately. But this did not happen. Here
are the results:
net Q top plate net Q bottom plate
+22 -18
+12 -8
-70 +76
In all three cases the Al blocks were discharged before separating
pieces of lexan (discharging time ~ 5 seconds). Do not attach any
significance to differences between the absolute values of Q in each
line; these are within our experimental errors (parallax, etc.).
We see familiar fluctuations in magnitude of Q, we see a familiar
sign reversal. This seems to indicate that net charges are produced
when lexan sheets are separated from each other. In this case
positive and negative are practically equal. According to the textbook
model there should be no net Q left on two pieces of lexan after
discharging the capacitor. And each half should also be zero after
the separation; we must repeat the test which shows that frictional
electrification does not occur in the process of separating two lexan
sheets in the process at zero volts. We did it last week to rule out the
piezoelectric effect.
Perhaps this was the first step toward sensible data, who knows?
At the very end three more measurements were made on a single
lexan sheet (0.3 mm) which was not coated. With 5000 V the net
charges were Q=-16, -76 and +76 units. A carbon-coated lexan was
again showing Q=0 under identical conditions. It feels good to see
that at least something is reproducible.