Date: Tue, 11 Jul 2006 02:58:22 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: cigrette lighter or silver socket - amp problem with air
compressor
In-Reply-To: <gk56b2hj45njs9pjscc5j6h4pnvgevgssk@4ax.com>
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At 08:30 PM 7/10/2006 -0700, BA wrote:
Hmm...may I fiddle with this a little? I think there are at least a
few points there that may be a bit confusing.
Lessee...ok. Electrical circuit is very like a plumbing circuit, but
mebbe even better to think of a hydraulic circuit, because the
purpose of each is to do work rather than supply a
substance. Hydraulic circuit transmits mechanical work as the
product of pressure drop and the actual quantity of hydraulic fluid
that flows through the point where work is being
extracted. Electrical is very nicely analogous: it transmits work as
the product of *potential* drop and the actual quantity of electrons
that flows through the point where work is being
extracted. "Potential" is an electrical word that means, well,
pressure. You can see the word itself refers to the
intensity/fury/projected ability/puissance/potency etc. to imbue each
electron in the flow with the ability to carry out *that* much work
by actually pushing on the next in line. When you get up to a
pressure drop of 25,000 volts or so the shove is so hard that if
there's a gap in the wire terminated with a one-inch ball at each end
the electrons will leap across an inch of dry air to escape the
crowding from the electrons piling up inside the ball. Even with
that force electrons are so small that it takes a great many to
accomplish anything noticeable on our scale, which is why we don't
die every time we scuff our feet on the carpet. ONE AMPERE is the
flow rate that will suffice to accomplish ONE WATT of work at a
pressure drop of ONE VOLT, and the number of the Holy COULOMB of
Antioch is verily the same [ok, they're not the same, but from this
distance they might as well be, just the same as how all those
Left-Coast people think I live in New York City and I'm equally
convinced the Angelinos and the Albucolloquians wave to each other in
the street every morning] as Avogadro's number which was once
tattooed on your skull somewhere in high-school chemistry. Roughly
600 000 000 000 000 000 000 000 New Yorkers storming the subway every
second, so heedless they warm the place up from rubbing against
it. And the amount of obsticality or RESISTANCE lying about that
will extract ONE WATT of power every second from ONE AMPERE (which is
6x10^23 electrons every second) under the maddening goad of ONE VOLT
of pressure drop is -- ONE OHM.
Oh yeah...capacitor is like a section of pipe with a rubber diaphragm
blocking the middle. Shove fluid in from either direction and it
gets harder and harder as you stretch the diaphragm one way or
t'other, and . You can store work that way, by pressing against the
springiness of the capacitor. You can also transmit work continously
right through it even though it blocks any continuous flow. I'll
take that hall pass, Tonstant Weader And if you need to store more
work than you can ram into a big capacitor, or maybe you need it to
come already stored...arrange to hang onto those electrons chemically
instead of just by overt shoving and you have invented a PRIMARY
(comes already filled with all the work it's going to be able to
supply) or SECONDARY (BYO electronic seltzer bottle and CHARGE IT
whenever it runs low) BATTERY. Which looks amazingly like a big
capacitor if you squint just so; and a very very large capacitor
looks remarkably like a rather small battery. A ONE FARAD capacitor
will accommodate ONE COULOMB of electrons AKA ONE Amp-SECOND if you
apply ONE VOLT of pressure across it. And to the eye-popped disbelief
of those of us old enough to know why the electron has a cross on his
tail (see NOTE below), they're actually making capacitors lately the
size of a New Jersey blueberry that have a capacity of ONE FARAD and
voltage rating of a few volts. If there was an article of faith in
my generation I believe it was that we would never get close enough
to a one-farad capacitor to see the whole building at once...'stonishing.
[Note:] Answer: Ben Franklin guessed -- wrong. And so for hundreds
of years people quite knowingly did all their electrical calculations
upside-down and backwards serene in the knowledge that the answers
worked perfectly well. Around ?1975? some bright spark struck a blow
for correctness and got the tech schools to teach negative current
instead of positive current to the new crop of baby techs. And now
any time technicians want to talk electricity with each other, they
have to agree ahead of time whether to talk positive or negative
current. And the answers are the same as before, except when someone
accidentally shifts midstream to whatever form they growed up
with. I'm sure someone must be very proud.
And if you like this little story I'll try to do another piece of it
in a week or two. But in fact if you wanted to stretch a bit and
were bored with crosswords, it's pretty remarkable how far you could
get with those two paragraphs, a suitable stick to scribble with and
a month lease on a deserted beach. Preferably one where the tide
didn't erase it every night.
>Capacitance is a well that's somewhere along the pipe. For a while,
>the water fills the well and doesn't continue along the pipe. But if
>you fill up the well and keep adding water, then the water simply
>keeps on flowing in the pipe. If you increase the pressure, the water
>doesn't fall into the well but just goes straight through the pipe
>(that's a blown capacitor!).
>
>A resistance is a narrowing of the pipe. (Or, a widening of the pipe
>which would provide less resistance rather than more).
>
>Amperage is how much water is flowing through the pipe.
>
>Voltage is how much pressure there is on an end of pipe caused by the
>pressure of the water on that end of the pipe.
>
>Batteries and generators are water pumps.
>
>Any more that I've missed out?
>
>
>
>If you don't understand it using the plumbing analogy, then there's
>another lovely analogy. It's in the book "There Are No Electrons:
>Electronics for Earthlings" ISBN 0962781592.
>
>
>B&S
>'87 Westy 'Esmerelda Blanc'
>SoCal
--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage," '85 GL "Poor Relation"
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