I am sorry for deleting the “Bob Sciamanda wrote:” line after responding
to Brian’s question in my last message. Let me return to Bob’s concern.
Consider a “another source” near the disectable capacitor, perhaps the
column of a Van de Graaff machine. What is the worse possible scenario?
The free charges( +Q1 and -Q2 on the opposite aluminum blocks of our
setup) are no longer equal in magnitude. So what? We are not interested
in free charges on metallic plates. We always get rid of them by discharging
the setup before the removal of dielectric sheets. The observed net charges
are presumably bound to sheets.
how can "the proximity of other conductors (grounded or not) could
complicate the situation"? How can other sources contribute to the
net bound charges appearing on dielectric plates?
Ludwik Kowalski
P.S.
Most of us are familiar with electrophorus of Volta, the precursor
of high voltage machines. Or with a parallel plates air capacitor in
which the distance between plates, d, is changing. Start with two
plates separated by d=1 mm, charge them to 100 V. Then separate
them so that d=100 mm. The d.o.p. will jump to nearly 10,000 V,
assuming Q=C*V=cost.