* * *
b) Mark Shapiro said (see below) that the conservation of charges should
be used. This would be OK if the electric neutrality of a battery could
be taken for granted. I suspect that explaining what is going on in a
battery, or in a power supply, is harder than explaining a capacitor.
In fact, I usually treat the equality of charges as a "self-evident
truth" and students accept this without questionning. But this time
the why-this-happens question was asked and I must answer it tomorrow.
Unless something better is suggested I will talk about the conservation
of charges (a never contradicted law of nature) hoping that nobody will
challenge the remark that the electric neutrality of a source can be
taken for granted. I know this to be true but I can not say that this
is also a law of nature. If I am really pressed I will say "ask your
chemistry professor". I know, however, that the topic is usually not
covered in the introductory chemistry courses, except in the form of
"as you know from physics, ...."
Ludwik Kowalski
* * *
Ludwik,
In accordance with your philosophy of preferring experimental
arguments, have the students make a battery from a NEUTRAL system
consisting of two (dissimilar) metal electrodes, an electrolyte and a
container.