On Wed, 6 Oct 2004 14:44:17 -0700, "El Conjeturar"
wrote:

How about:
average power =

where V and I are understood to be the effective or rms values of the
voltage and current.

No, no, no! RMS and average are two totally different things!
--

"What is now proved was once only imagin'd." - William Blake, 1793.

Read the URL
http://hyperphysics.phy-astr.gsu.edu...c/powerac.html

it did not say rms equals average

The page was written by a Carl R. (Rod) Nave Department of Physics and
Astronomy Georgia State University

a.. Associate Professor, Georgia State University
a.. Faculty Advisor, Undergraduate Program
a.. Author, HyperPhysics
..



"Paul Burridge" wrote in message
...
On Wed, 6 Oct 2004 14:44:17 -0700, "El Conjeturar"
wrote:

How about:
average power =

where V and I are understood to be the effective or rms values of the
voltage and current.

No, no, no! RMS and average are two totally different things!
--

"What is now proved was once only imagin'd." - William Blake, 1793.

Only quantities which have been arithmetically derived by the equation -

P = Sqrt( Sqr(A) + Sqr(B) + Sqr(C) + . . . )

or its equivalents, can properly be referred to as RMS.

Occasionally, when there is something specially significant in the way a
value been calculated, it may be descriptively convenient to precede its
name with RMS.

But use of the term in a non-arithmetical context s meaningless.

The term 'RMS value' is also used in conjunction with other than electrical
quantities, eg., as in Statistics.
----
Reg.

On Wed, 06 Oct 2004 13:38:19 -0700, Bill Turner
wrote:

On Wed, 06 Oct 2004 18:15:11 GMT, Gary Schafer
wrote:

How about "average power" the correct term.

_________________________________________________ ________

This will be the third time I've asked for an official source for this
"correct" term. If there is no reply, I shan't be asking again.


References:

Same one I gave before in an earlier post.
2000 ARRL handbook 6.6 chapter 6, RMS VOLTAGES AND CURRENTS. Read on
to the pep power paragraph too.

Here is another:
Here are quotes directly from: Electronics Pocket Handbook by Daniel
L. Metzger. Page 13.
This is a nice little book if you ever run across one pick it up.
About 280 pages.

Peak, Average and rms.

1. Use peak voltage or current to calculate maximum instantaneous
power only.

2. Use average current to calculate average power when the voltage is
fixed dc. Use average voltage to calculate average power when the
current is unvarying dc.

3. Use rms voltage and /or rms current to calculate average power when
the load is a linear device (resistor) and both V and I are ac in
phase and of the same waveshape. Use IV, I^2 R, V^2/R.

4. Rms measure is assumed in any ac voltage or current notation unless
peak, peak to peak, or average is specified.

5. The factor .707 for converting peak to rms applies to sine waves
only.

73
Gary K4FMX

Bill, here's the story.

RMS and average are basic mathematical functions whose definitions you
can find in numerous references(*). I'll state them here.

The average value of any periodic function is the time integral over a
cycle of the instantaneous value of the function, divided by the period.

The RMS value of any periodic function is the square root of the average
(mean value) of the square of the function, where the average is defined
as above.

First, let's look at these two values for a sine wave with peak
amplitude of V. The instantaneous value (value at any time t) is V *
sin(wt) where w is omega = 2 * pi * frequency. The integral over a cycle
is zero (since the wave spends equal amounts of time at equal amplitudes
above and below zero), so the average value is zero. Some careless
references will give a non-zero value for the "average" of a sine wave,
but this is really the average of the absolute value (that is, the
full-wave rectified value) of the sine wave. The actual average value of
a sine wave with no DC offset is zero. (If it has a DC offset, the
average value is simply the value of the offset.)

The RMS value of the sine wave is the square root of the average of the
square of the original sine function, which is V^2 * sin^2(wt). If you
graph this, you see that it looks like a rectified sine wave -- it never
goes negative. If you go through with the math to get the average of
this squared function, you get the nice value of V^2 / 2 for the
average, hence V / sqrt(2) ~ 0.707 * V for the RMS.

Now let's apply that sine wave to a resistor and look at the power.

The *instantaneous* power, that is the power at any instant, dissipated
by the resistor is v * i = v^2 / R where v is the instantaneous value of
the voltage: v = V * sin(wt). So v^2 / R = V^2 * sin^2(wt) / R. Look
familiar? So what's the average power? Using the definition of average,
the average power is the integral over a period of the instantaneous
power, divided by the period. In other words, it's average value of V^2
* sin^2(wt) / R. Looking at what we did to get the RMS voltage above,
you can see that the average power is simply the square of the RMS
voltage, divided by R.

That's why the *average* power is the square of the *RMS* voltage
divided by R. It's important to realize that this holds true for any
periodic voltage function -- square wave, triangle wave, what have you.

You can use the basic definition of RMS to calculate an RMS value of
power from the instantaneous power, but it's not useful for anything. A
resistor dissipating 10 watts of average power gets exactly as hot if
that average power is supplied by DC, a sine wave, or any other
waveform. That's not true of the RMS power -- different waveforms
producing the same average power and causing the same amount of heat
will produce different RMS powers. So average power is a very useful
value, while RMS power is not.

The only thing that makes RMS voltage or current useful at all or
worthwhile calculating is its relationship to the useful quantity of
average power.

(*)You were asking for references -- you can find the definition of
average on p. 254 and RMS on p. 255 of Pearson and Maler, _Introductory
Circuit Analysis_, and average on p. 423 and RMS on p. 424 of Van
Valkenburg, _Network Analysis_. You'll also find an explanation in both
books similar to the one I just gave. These happen to be the two basic
circuit analysis texts I have on my shelf -- you should be able to find
the same explanation in just about any other circuits text.

Roy Lewallen, W7EL

On Thu, 07 Oct 2004 09:04:08 -0700, Bill Turner
wrote:

On Thu, 07 Oct 2004 01:28:13 -0700, Roy Lewallen wrote:

You can use the basic definition of RMS to calculate an RMS value of
power from the instantaneous power, but it's not useful for anything. A
resistor dissipating 10 watts of average power gets exactly as hot if
that average power is supplied by DC, a sine wave, or any other
waveform. That's not true of the RMS power -- different waveforms
producing the same average power and causing the same amount of heat
will produce different RMS powers. So average power is a very useful
value, while RMS power is not.

_________________________________________________ ________

That goes against everything I've ever read about RMS power, at least
for sine waves. I have always heard that a certain value of RMS power
produces the same heating as the same value of DC power. In your
statement above, you say that's true only for average power, not RMS,
and is true for *any* waveform, including sine waves.

Is there a new world order?

Bill,

If you read carefully in any of the handbooks where they discuss the
resistor heating by AC compared to DC you will see that they say "RMS
VOLTAGE that causes the same amount of heating in a resistor as the
same amount of DC voltage". They do not say the same amount of RMS
power.

Since a constant DC voltage would equate to average power in a
resistor, then if the same amount of AC RMS voltage causes the same
amount of heat it has to also be average power that it produces.

73
Gary K4FMX

Bill Turner wrote:
On Thu, 07 Oct 2004 01:28:13 -0700, Roy Lewallen wrote:


You can use the basic definition of RMS to calculate an RMS value of
power from the instantaneous power, but it's not useful for anything. A
resistor dissipating 10 watts of average power gets exactly as hot if
that average power is supplied by DC, a sine wave, or any other
waveform. That's not true of the RMS power -- different waveforms
producing the same average power and causing the same amount of heat
will produce different RMS powers. So average power is a very useful
value, while RMS power is not.


__________________________________________________ _______

That goes against everything I've ever read about RMS power, at least
for sine waves. I have always heard that a certain value of RMS power
produces the same heating as the same value of DC power.

I'd be interested in where you've read this. It's wrong. I suspect that
if you go back and read carefully, you'll find that it's the RMS value
of the voltage or current that causes the same heating as the same DC
value, not the RMS value of the power.

Incidentally, I should mention that "RMS power" is used by the makers of
audio amplifiers. About four years ago, this topic came up on
rec.radio.amateur.antenna, and Jim Kelley commented about it:

Jim Kelley wrote:

I found out the answer to this usage of RMS power. The audio folks
have co-opted the RMS idea to mean the following: If the signal is a
single sine wave, then RMS power is understood to mean the average
power output due to that sine wave. It is deceptive to the following
extent: An amplifier with a certain "RMS power rating" may go
completely flat on peaks that are only a little greater than the RMS
rating. Anyway, the use of the term is pervasive.

So the term is sometimes used in the consumer audio world, although
incorrectly. One shouldn't look to the audio consumer world for accurate
technical information about anything.

In your
statement above, you say that's true only for average power, not RMS,
and is true for *any* waveform, including sine waves.

Let me demonstrate my statement about the average power being the square
of the RMS voltage divided by R for any waveform.

Call the voltage time waveform v(t). This was V * sin(wt) for my sine
wave example, but let it be any periodic waveform. The RMS value of the
voltage Vrms is, by definition, sqrt(avg(v(t)^2)). Applied to a
resistor, the power time waveform p(t) is v(t)^2/R, so the average power
is avg(p(t)) = avg(v(t)^2/R) = avg(v(t)^2)/R. (The 1/R term can be moved
out of the average since it doesn't vary with time -- the time average
of 1/R = 1/R.) From the definition of RMS voltage, you can see that
avg(v(t)^2)/R is simply Vrms^2/R. This was demonstrated without any
assumption about the nature of v(t) except that it's periodic.

The RMS power caused by that v(t) waveform would be sqrt(avg(p(t)^2)) =
sqrt(avg(v(t)^4/R^2)) = sqrt(avg(v(t)^4))/R. This is different from the
average, with the size of the difference depending on the shape of the
waveform.

Is there a new world order?

No, but hopefully there's some new knowledge being gained.

Roy Lewallen, W7EL

"Bill Turner" wrote in message
...
On Wed, 6 Oct 2004 16:15:23 -0500, "Steve Nosko"
wrote:

3- I disagree. An adjective or modifier isn't "needed" but it sure can
help
if there may be confusion as to just what the subject is.

__________________________________________________ _______

I think we're having a semantic-fest here. Steve says an adjective
isn't "needed" but can help if there may be confusion.

Well, if it helps avoid confusion, isn't it "needed". Or is confusion
ok?
--
Bill W6WRT

Oh, I suppose, but I maintain this is something you determine within the
discussion, then move on to cover the important aspects of the issue at
hand. After moving on, you won't have to keep saying "Average Power' (or
whatever is decided upon) each time you want to refer to it. You will just
need to say "power", since you have defined the term. This is a
semantic-fest, rather than a discussion of how to determine power. I've
been in many, many discussions, where once the subject is defined, the word
"power" is used repeatedly, never with any adjectives and no one had any
problems.

You guys are too tied up in what is "official". It is what is in common
usage that matters. define your terms and move on.
73
--
Steve N, K,9;d, c. i My email has no u's.

"Bill Turner" wrote in message
...
On Wed, 06 Oct 2004 18:15:11 GMT, Gary Schafer
wrote:

How about "average power" the correct term.

__________________________________________________ _______

This will be the third time I've asked for an official source for this
"correct" term. If there is no reply, I shan't be asking again.

--


What is official to you? It appears you are not sure what the word
'average' means.

Ask Jeeves gave quite a few official looking references for a search of
"average power"
http://ask.com/
See the ones that look like dictionaries of glossaries.

See the "graphics version":
http://www.abdn.ac.uk/physics/bio/fi20www/tsld016.htm



A search via Google and some poking around just gave me:
hyperphysics.phy-astr.gsu.edu/ hbase/electric/powerac.html
http://mitglied.lycos.de/radargrundl...r/pr22-en.html

http://www.twysted-pair.com/dictp.htm


http://www.csgnetwork.com/ohmslaw2.html

Power used by the human body on this one:
http://www.csgnetwork.com/ohmslaw2.html

Look Ma, No adjectives:
http://www.ffldusoe.edu/Faculty/Dene...0&%20%20energy



This should confuse you even more.
http://www.tpub.com/content/neets/14...s/14192_15.htm

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.


--
Steve N, K,9;d, c. i My email has no u's.

"Bill Turner" wrote in message
...
On Thu, 07 Oct 2004 01:28:13 -0700, Roy Lewallen wrote:

You can use the basic definition of RMS to calculate an RMS value of
power from the instantaneous power, but it's not useful for anything. A
resistor dissipating 10 watts of average power gets exactly as hot if
that average power is supplied by DC, a sine wave, or any other
waveform. That's not true of the RMS power -- different waveforms
producing the same average power and causing the same amount of heat
will produce different RMS powers. So average power is a very useful
value, while RMS power is not.

__________________________________________________ _______

That goes against everything I've ever read about RMS power, at least
for sine waves. I have always heard that a certain value of RMS power
produces the same heating as the same value of DC power. In your
statement above, you say that's true only for average power, not RMS,
and is true for *any* waveform, including sine waves.

Is there a new world order?

--
Bill W6WRT


Bill,
Please be careful here. You are confusing yourself. The passage you
quoted here is indeed correct, but I believe you are interpreting it
incorrectly because you are thinking of the term "RMS Power" as the "loosely
defined" term in the audio world also spelled "RMS Power".
The above passage is indeed correct IF you understand that it is
referring to an RMS value of the power waveform. (one of the links I posted
previously shows a power waveform in the "graphics version" link) This is a
mathematically defined "Root Mean Square" value of the power waveform. THIS
does indeed have no use. Calculating the Root-Mean-Square of a power
waveform does NOT produce the average power we think of as heating the same
as DC. We don't do it and in the Engineering community we don't use that
term at all. We talk about the 'true' or 'average power' to make things
clear, if needed.
However, the term bandied about in Audio circles which is also spelled
"RMS Power" means something completely different. One term - two meanings.
It has been used (as I gather from earlier posts) to mean what would be
correctly describes as: the average power produced by a channel of an audio
amplifier under sinewave signal conditions. This describes what is
technically called "Average Power", but the audio folks saw a need to have
something to hang their hat on we=hen talking about this measurement and,
unfortunately picled something just to confuse you, Bill.
This is two different uses for the same phrase. The first is a
mathematically defined value (the same math used to get RMS voltages) and
the other is a commonly accepted meaning in a specific field.

Both can be correct IF you understand which deffinition is in use.

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.




--
Remove 'X' to reply via e-mail.
Linux 2.6.7

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. . .

Bill Turner wrote:
On Sat, 9 Oct 2004 18:37:01 +0100, "Ian White, G3SEK"
wrote:

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

_________________________________________________ ________

I am mildly curious how long this error will be propagated. Surely it
will still be around after I'm gone, but will engineers five hundred or
a thousand years still be defying logic?


Faraday established the convention that "current" flows from "positive"
to "negative" in 1834.

Thomson discovered the electron in 1897, and found it had a negative
charge.

But even then, it was already far too late to think about changing the
convention about "current". Scientists who had to work with electrons
would have to learn to live with it.

And if it was already too late in 1897...

Not a big deal, but it is fascinating to me how nobody will take the
bull by the horns and fix it.

There really ain't much that's needful of fixin'. Electrical engineering
was growing and thriving before electrons were discovered, and a century
later, everything still works. Even "electronics" hardly ever has to
think about electrons, or the sign of their charge. We're doing just
fine, thank you.

It's an untidy world, Bill. Please get over it... soon :-)



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

I think the question is why should engineers, who have designed
everything from communications satellites to cell phones to the computer
you're using, your ham radio rig, and countless other things over the
past couple of hundred years, change their methods? Because Bill isn't
able -- or willing -- to understand the difference between charge and
electrons?

Sorry, you haven't managed to convince even one engineer, and you've got
millions to go. Good luck.

Roy Lewallen, W7EL

Bill Turner wrote:
On Sun, 10 Oct 2004 09:04:30 +0100, "Ian White, G3SEK"
wrote:


It's an untidy world, Bill. Please get over it... soon :-)


__________________________________________________ _______

When I was a little boy, that argument would not have worked with mom.
I still had to clean my room.

If only mom had been an electrical engineer... "Gosh mom, my room has
always been like this. Why change things now?"

:-)

--
Bill W6WRT

"Bill Turner" wrote in message
...
Where I draw the line is those few engineers - and I've met some - who
believe that current really, really does flow from plus to minus, and
it's a *real* flow, not just some mathematical concept.

Hole flow in semiconductor devices, which represents a positive charge
current, and certainly can be from 'plus to minus,' is arguably 'real.'

I would agree with you that anyone who seriously misunderstands any of this
and claims to be a practicing electrical engineer should be viewed with a
little skepticism. :-) If you're working with numerous such individuals, it
might be time to look for other jobs...