Bill Turner wrote:
On Fri, 08 Oct 2004 16:01:04 -0700, Roy Lewallen wrote:

It's a common mistake to equate "current" or "charge" with "electrons",

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What other kind of current is there besides the flow of electrons? Even
the flow of "holes" in a semiconductor is propagated by the absence of
electrons.

And isn't charge merely the presence or absence of electrons? I'm not
talking mathematical concepts, just the actual physical happening?

One last try...

When you look at the history, "current" and "flow of electrons" truly
*are* two different things. They come from two different centuries of
science and engineering.

"Current" came first. As people invented electrical devices such as
batteries, electromagnets, motors and generators, the concept
developed that "electric current" must in fact be a flow of charged
particles.

However, you can't experiment on a battery without labeling the
terminals, so the convention that "current flows from positive to
negative" had to be established very early (by Faraday, I believe).

The new technology of electrical engineering forged ahead for several
decades without ever needing to know what those fundamental charged
particles were. Faraday himself never knew. When the electron was
finally identified, it was found to have a negative charge - which meant
that what people had been calling "current" is actually a flow of
electrons in the opposite direction.

But by then there was absolutely no question of changing the conventions
of what "current", "positive" and "negative" mean. Those conventions
remain unchanged to this day.

That was how we were taught it in school, at age 12:

"Here's all the history" (as above, only with dates... which I've
forgotten).

"Hard luck that the electron turned out to have a negative charge. It
makes life a bit more complicated."

"'Current' is not the same as 'flow of electrons', because they're going
in the opposite directions. Be careful to say the one you actually
mean."

"Don't worry, you'll learn to cope with it" - and so we did.


It's only hard if you insist on *making* it hard.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek