Basic Electricity by David Beierl
From VanagonWiki
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.
[edit] List Archive Links
David Beierl - 11 Jul 2006
