Steve Nosko wrote:

Then I found this !!
Looking for average power? eBay has great deals on new and used electronics,
cars, apparel, collectibles, sporting goods and more. If you can t find it
on eBay, it probably doesn t exist.

Be thankful you weren't looking for 'average length'.

73, Ed. EI9GQ.




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Bill,

Did you read what I wrote?

Or perhaps you don't believe it? If not, just pick up any textbook on
basic electric circuit theory, where you'll find essentially the same
explanation.

Roy Lewallen, W7EL

Bill Turner wrote:
__________________________________________________ _______

Ok, I grant you that, but as I see it, in a resistive circuit RMS
voltage causes RMS current to flow and the resultant power is RMS power.
Why not?

If DC volts x DC amps = DC power

and

Peak volts x peak amps = peak power

then why does not

RMS volts x RMS amps = RMS power?

If you want to say that RMS power is the same as average power, I can
live with that, but why say that RMS power is a meaningless concept?

Oh well. You guys have given it a good try, but I remain unconvinced.

Perhaps we should move on to the question of whether current flows from
plus to minus or minus to plus. A lot of otherwise good engineers
actually believe it to be the former. I love to hear them explain how a
vacuum tube works. :-)

--
Bill W6WRT

"Bill Turner" wrote in message
...
I'm becoming convinced this is more a question of semantics or of
somebody's arbitrary definition than one of actual fact.

I'm think it's more a question of consistency. If you define RMS voltage
and current a certain way (that we're all in agreement with), it stands to
reason that "RMS foo" should have a comparable definition. As Roy has
shown, using that same definition makes "RMS power" of questionable utility.

The fact that 'the audio guys' don't use that definition is unfortunate and
something to be aware of, but arguably not something to be encouraged. :-)
(On the other hand, getting the audio guys to agree to _any_ definitions can
be dicey... their usage of 'RMS power' was motivated by other terms such as
'PEP' -- peak envelope power -- that have almost nothing to do with the
utility of the amplifier whatsoever. It's not uncommon to see '100W PEP'
amplifiers that come with little wall warts capable of delivering no more
than, say, 3W average power.)

Certainly there is such a thing as RMS power. It just isn't useful for
anything. The definitions I used aren't arbitrary at all, but widely
accepted and agreed upon. It's true that some amateurs and consumer
audio marketers have chosen not to use the accepted definitions, but
their inventions shouldn't be given equal weight to ones which have been
used for centuries and are universally accepted by the math, physics,
and engineering communities.

What's the problem with current flowing from plus to minus? I believe it
was Ben Franklin who realized that there are two polarities of charge,
and arbitrarily called one plus and one minus. If he had made the other
choice, positive or negative charge would indeed flow the other way.

I've been through technical school, where current was considered to flow
from minus to plus, and engineering school, where the opposite
definition was used. You can use either method and arrive at the correct
answer, but you end up with quite a few more minus signs with the
minus-to-plus convention. Since engineering is highly mathematical, the
plus-to-minus convention makes sense for engineering because of the
somewhat simpler equations that result.

I've always thought that tech schools used the minus-to-plus convention
because it made it easier for students to get an intuitive feel for how
a vacuum tube operates. (It's hard to imagine positive charge leaving
the plate and condensing on the hot cathode!) Now that fire-fets are
(like some of us) largely relics of the past, and the importance of good
communication between technicians and engineers is recognized, I'd be
surprised if the minus-to-plus convention is still being taught even in
tech schools -- if anyone has any recent information about this, I'd be
interested to know.

Roy Lewallen, W7EL

Bill Turner wrote:
On Fri, 08 Oct 2004 11:08:35 -0700, Roy Lewallen wrote:


Did you read what I wrote?


__________________________________________________ _______

Yes, of course.

I'm becoming convinced this is more a question of semantics or of
somebody's arbitrary definition than one of actual fact.

My real disagreement is with the statement "There is no such thing as
RMS power". The rest of the arguments here I have no real quarrel with.
As far as I can tell, all the math presented here is correct, with the
exception of the fellow who the wrong factor when converting RMS voltage
to peak power.

To each his own.

Now, what about that current flow from plus to minus? :-)

--
Bill W6WRT

On Fri, 08 Oct 2004 12:36:06 -0700, Bill Turner
wrote:

On Fri, 08 Oct 2004 11:08:35 -0700, Roy Lewallen wrote:

Did you read what I wrote?

_________________________________________________ ________

Yes, of course.

I'm becoming convinced this is more a question of semantics or of
somebody's arbitrary definition than one of actual fact.

My real disagreement is with the statement "There is no such thing as
RMS power". The rest of the arguments here I have no real quarrel with.
As far as I can tell, all the math presented here is correct, with the
exception of the fellow who the wrong factor when converting RMS voltage
to peak power.

To each his own.

Now, what about that current flow from plus to minus? :-)


You may be reading what people wrote but you are doing selective
reading. You are only letting through things that agree with your
preconceived beliefs and blocking out the logic.

You have the bandwidth cranked in too tight, the notch filter set too
deep on the wrong side of the pass band and the noise blanker on. You
are complaining how bad the signals sound but if you read the manual
you may be able to clear the problem. :)

Roy said that there is rms power but that it has nothing to do with
average power that we get when rms voltage and current are multiplied.

I and others have said that there is no such thing as rms power. That
is not a stand alone absolute fact obviously but in this context it is
meaningless.

You can find the rms value of any periodic wave just like you find the
rms value of voltage or current. But finding the rms value of power is
of no value. And you don't get it by multiplying rms voltage by rms
current. Again, once you multiply an rms value by another rms value
the answer you get is not rms.

Rms is not a title. It is the result of a mathematical operation.

Average power and rms power are not the same.

73
Gary K4FMX

It's too bad you've chosen to limit your thinking in this way, but as
long as you can fit everything that interests you into the box you've
created, I guess it doesn't cause you any problems. I'd think you'd have
to avoid such topics as lightning and positive ion generators, though.

It's a common mistake to equate "current" or "charge" with "electrons",
but probably no more common than lack of understanding of what RMS and
average mean. A lot of people seem to manage to maintain a more-or-less
consistent view of electricity while carrying around some pretty
mistaken ideas. In my experience, though, now and then they end up
really stumped by something, while someone with a more complete view of
basic electrical physics has an easy time understanding and analyzing
what's going on. We all make our choices.

Roy Lewallen, W7EL

Bill Turner wrote:

On Fri, 08 Oct 2004 13:59:57 -0700, Roy Lewallen wrote:


What's the problem with current flowing from plus to minus?


After much head-scratching, the only problem I can see is that it
doesn't. It flows from minus to plus.




I believe it
was Ben Franklin who realized that there are two polarities of charge,
and arbitrarily called one plus and one minus. If he had made the other
choice, positive or negative charge would indeed flow the other way.


Murphy triumphs again.

What you say about the mathematics being made easier I can agree with.
The trouble is, some engineers take it a step further and say "yes,
current *really* does flow from plus to minus." I then ask them to
explain how a vacuum tube works, especially why it needs a hot cathode
to "accept" electrons. Blank stares.

Ah, well.

--
Bill W6WRT

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",

_________________________________________________ ________

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

It's a universal tendency for people to simplify things in order to
understand them. That's fine, as long as they realize that their
understanding is based on a simplification, and they don't try to apply
it to areas where the simplification is no longer valid. While the idea
of charge flow as electron flow works just fine in a vacuum tube, it
isn't at all true in general.

Current is the rate of flow of charge, which as I'll explain isn't the
same as the flow of electrons. Charge can be positive or negative. A
shortage of electrons in an atom's valence shell results in a positively
charged atom (a positive ion), and an excess of electrons in a
negatively charged one (a negative ion). In a conductor, electrons are
quite free to move about. In a semiconductor, they're not, and the
crystal lattice can contain either an excess of electrons (N type
material), a deficiency of them (P type material), or a normal number
(intrinsic material). In a vacuum tube, the flow of (negative) charge is
simply the physical flow of electrons, and the flow of positive charge
becomes a mathematical concept, moving the opposite direction. But this
isn't necessarily so in other media. In a wire, for example, charge
flows much faster (near the speed of light) than electrons (which flow
at a rate on the order of a few miles per hour). If you jam a bunch of
electrons into one end of a wire, an equal number very quickly pops out
the other -- but these aren't the same ones that went into the other end
-- those will slowly drift along the wire at a few miles per hour. The
rate of charge flow is dictated by how long it took electrons to pop out
of the other end of the wire after jamming some in the input end, not
how long it takes the added electrons to drift their way along. So in a
wire, for example, charge isn't the same as movement of electrons. If
you try to envision physical current (charge flow) in a wire as being
the same as physical current in a vacuum tube, you'll be misleading
yourself.

Now imagine sucking a bunch of electrons out of one end of the wire.
There'll be an electron-poor region at the wire end. A "wave" of
electron-poor region will propagate to the other end of the wire at
nearly the speed of light, and a bunch of electrons will be sucked into
the other end of the wire. The propagation of this wave of an
electron-poor region is the physical flow of positive charge. Envision,
if you must, sucking water through a drinking straw that's already
filled with water. Bear in mind, though, that this isn't an exact model
of what's happening, so be careful in using it.

It's important to be able to separate the concepts of moving charges and
moving electrons, if you're going to have the versatility of
understanding things other than vacuum tubes, like positive ion
generators, lightning, charge flow in a semiconductor, or even a wire.
Once you do, it becomes just as easy to envision positive charge flow as
negative charge flow. If you can't do this without imagining physical
marble-like particles carrying the charge, you have no hope of
understanding an electromagnetic field, or other more abstract and
mathematical concepts.

Roy Lewallen, W7EL

-- A quick web search brought this brief explanation of how electrons
behave in a conductor:
http://hyperphysics.phy-astr.gsu.edu...ic/ohmmic.html. I'm
sure it would be easy to find a lot more good information (as well as
some pretty bad stuff) if anyone is interested enough to look.

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",


__________________________________________________ _______

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?

--
Bill W6WRT

It's a universal tendency for people to simplify things in order to
understand them.

=============================

The universal tendency on this newsgroup is to overcomplicate things to
further confuse matters. (If that's possible).

There's nothing better than a very few carefully chosen words of plain,
simple, factual English language.

Responders should very carefully edit and summarise what they have to say
before hitting the 'send' key.

I hasten to say, Roy, you certainly do not fall into the 'careless'
category.

I am at present on Californian red Zinfandel. Where it got its name from I
can't imagine. But on the side of the bottle it says it should be consumed
within 1 year of purchase. There is still 364 days to go.
----
Reg, G4FGQ

Correction:

The speed of electron flow in a conductor is more like a few feet per
hour rather than a few miles per hour as I said, at reasonable current
levels and wire sizes (but depending on the current and the wire
diameter). The numerical example for copper shown at the web site I
mentioned shows an electron drift velocity of 4.3 mm/s for a 1 mm
diameter wire with 46 A current (which would probably explode the wire).
This works out to about 51 feet/hour. At the more reasonable current of
3 A, the electron drift velocity drops to 0.28 mm/s, or about 3.3 feet/hour.

The electron drift velocity is so slow because, even though an ampere of
current is a seemingly staggering 6 X 10^18 electron charges per second,
there are vastly more free electrons than this in even a small wire.
(Again see the web site example, where the density is shown to be about
8.5 X 10^28 electrons/m^3, or about 6.7 X 10^22 electrons in the 1 mm
diameter, 1 meter long wire in the example.)(*) Carefully using the
drinking straw analogy again, imagine a very large diameter drinking
straw (lots of free water "electrons"), where an ampere of current is
represented by a tiny trickle of water. If you suck water out one end at
the rate of "one ampere", it takes a long time for the actual water
molecules at the other end of the straw to work their way up the straw.

(*) You can, in fact, calculate the drift velocity somewhat more simply
and perhaps more intuituvely than the author of that page did, knowing
only the electron density and the size of the wire. From the wire size
you can calculate its volume as 7.85 X 10^-7 m^3. Multiplying this by
the electron density, you get the total number of free electrons it
contains, about 6.7 X 10^22. So the wire holds 6.7 X 10^22 / 6 X 10^18 ~
11,000 coulombs (ampere-seconds) of available charge. If we move charge
through at the rate of 46 amperes as in the first example, it would take
11,000/46 ~ 240 seconds for an electron to move from one end of the wire
to the other, a rate of one meter/240 seconds or about 4.2 mm/sec.
Within roundoff error, this is what the author calculated.

Roy Lewallen, W7EL

Roy Lewallen wrote:

. . .
In a wire, for example, charge
flows much faster (near the speed of light) than electrons (which flow
at a rate on the order of a few miles per hour). . .
. . .

-- A quick web search brought this brief explanation of how electrons
behave in a conductor:
http://hyperphysics.phy-astr.gsu.edu...ic/ohmmic.html. . .