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Re: more on capacitors



On Thu, 19 Feb 1998, Mark Shapiro wrote:

Don,

The bypass capacitors in a divider chain don't usually have either
of their plates connected to ground. They still supply charge to the
photomultiplier tube.

But the capacitors cannot supply net charge to the tube. They might
produce a current in the tube, but if the current takes a closed path,
then no net charge can leave or return to the capacitor.


The fact that some of that charge may end up back
on the other plate in no more relevant than the fact that current that
comes out of one terminal of a power supply goes into the other.

But it's extremely relevant. With power supplies, if no current (charge,
actually) is allowed to return to the other terminal, then no charge will
be able to exit the first terminal.

Would we
say that a power supply never supplies current just because the NET
current out it is zero?

They don't supply current. Current is not substance-like. I'd say that a
power supply causes *a* current to appear. Water analogy: I wouldn't say
that a water pump is a supply for current, I'd say that a water pump can
move water, or that it can cause a current to appear.


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