basic ac theory question

Realy? Ever heard of insulation transformer, nothing 'stays put' except if it is properly 'nailed' to something.

Have fun

Stanislaw.

On 10 Oct 2006 07:18:07 GMT, in message , jasen scribed:

How much charge is in a piece of wire with eight trillion electrons and no difference in potential across the ends?

You're quibbling over the use of the word "energy" as opposed to "force?" Or is the misunderstanding more fundamental? If this website is to be believed:

"The exertion of work by an external force would in turn add potential energy to the object."

then yes, the potential exerts force, which although you like to say "Nope," this in no way contradicts my statement that the application of this force is adding energy. Unless you misunderstand what I mean by "imparts?" Or maybe I misunderstand what you mean by "Nope?"

Er, so why does the definition of "ampere" refer to the movement of charge instead of the movement of potential? This is an interesting re-definition you've made. Please elaborate.

Missed the bit of sarcasm there, you did.

Are you trolling? This statement is a direct contradiction of one you made just a few sentences ago! Clean up your act!!

What?

On Mon, 9 Oct 2006 17:29:06 -0400, in message , "Tom Biasi" scribed:

Hey, thanks. I'm practicing for retirement, when I plan to go into teaching. So this is like work-study. Heh.

On 10 Oct 2006 07:21:49 GMT, in message , jasen scribed:

You have a fundamental misunderstanding of the discussion, and perhaps a fundamental misunderstanding of the relationship of current and voltage. In alternating current, it is just as Stosh says, the current, in *both* conductors, moves as a sinusoid, swinging back and forth on positive and negative half-cycles. Neither "stays put" if you like to use that term.

Where he makes a mistake is in referring to hot and neutral as exchanging places. Now the discussion moves into the realm of voltage, where indeed the black wire is always hot and the white wire is always neutral. The distinction being that the voltage in the white wire is "nailed" to ground potential, but the current is still moving, and certainly does not "stay put."

And the bird on the wire analogy is badly flawed. The current under the bird's feet is alternating 60 times per second. The voltage potential with respect to ground on the bird is also changing, at however many thousands of volts, positive to negative, 60 times per second. The bird is not adversely affected because the bird's relationship to ground potential is essentially zero. Neither the potential nor the current "stays put." A further problem with the analogy is that, in many transmission lines, neutral is not even present.

^^^^

60 cycles per second = 60 positive and 60 negative for 120 transitions.

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Michael A. Terrell
Central Florida

In my retirement I plan to go 'out' of teaching.

Quite a bit, actually - it's just that there is an equal amount of positive and negative charge. If all of those eight trillion electrons could magically be removed (that's a pretty small piece of wire, by the way), how much charge would there be then?

Fundamentally, "charge" refers to a basic property of subatomic particles, namely that property which causes them to produce an electric field. (Or at least that is one aspect of it - the fundamental force involved is the electromagnetic force, which also is responsible for magnetic fields.)

We can short this whole argument to ground (no pun intended..:-)) by simply noting that "current" (which is what "amperes" are used to quantify) is not technically the movement of charged particles themselves, necessarily, but rather the EFFECTIVE movement of charge. The addition of that one little word lets us talk reasonably about alternating current; even though there is no real net movement of charge carriers in one direction over the other, there IS a flow of "energy" which can be quantified by using notions of current, etc., just as if everything was "flowing" in one direction (as in the case of DC). This is just one of those areas where our mental model than uses a stream of water (or whatever) as an analog for electricity starts to look a little problematic. But once you remember that it really IS just a model, and not precisely a description of the real thing, the problems go away.

Bob M.

On Wed, 11 Oct 2006 21:11:36 GMT, in message , "Bob Myers" scribed:

But the ability of a conductor to conduct current is not dependent upon how many electrons it has, but rather how easily those electrons may be induced to move. A piece of glass and a piece of copper with equal amounts of electrons will have an equal *net* charge of zero in the idealized absence of an electric field. When a field is introduced - the application of a potential from one end to the next, the copper will much more easily acquire net charge differences at the molecular level. So, let's modify my statement to say that a piece of wire with no electric field present will have no net positive or negative charge.

So let's apply this to the statement I replied to:

"charge is a a number of electrons (or equivalent)"

That's very inaccurate. Let's get down to fundamentals, and look at how current is defined in a physical model. I'll substitute English letters for the Greek that is standard in the definition

I = pn*q*vd*A

vd = Drift Velocity pn = Number Density - Charges per unit Volume q = Magnitude of the charge on each moving charge A = Cross-sectional Area perpendicular to the flow.

So, charge can't be said to be a "number of electrons" unless there is some quantity that produces a charge due to the presence of potentially free electrons - IOW you won't have net positive or negative charge until something gets electrons moving. Am I correct so far?

Well I think that definition is pretty good, and I don't think it differs much from what I am trying to say. My comment comes from being a bit baffled by seeing current being referred to as the movement of potential, instead of the movement of charge. I'd like to see that explained. I mean, I can see that across a conductor that is conducting charge, that in taking slices of that conductor and measuring potential, one can see that potential changes over the linear distance of measurement. But how can that lead to a definition of current as being a movement of potential?! I just don't think that's right.

Let's take an example from a thread from a month or so ago, regarding the propagation of an electric field through the air. It can be seen and measured that the field strength decreases with distance from the transmitter. May that be considered a movement of potential? It is a travel ling electric field, but it is not current. Indeed, several posters were insisting that it's not even electricity. So, can we reconcile that definition? Or not?

On Wed, 11 Oct 2006 17:26:33 GMT, in message , "Michael A. Terrell" scribed:

I just *knew* somebody would do that! Ok, for the record, one alternation is one half cycle. Hmph.

what potential is it at? what is its capacitance?

no I'm just plain wrong there, the potential difference exerts force. (causing a flow)

the word work is significant there

also the energy doesn't go into the electrons - it ends up heating the wire

current propogates at speeds approaching C also. but charge doesn't move that fast (in conductors).

yeah I made a mistake above. potential exerts no force, a potential difference is needed for there to be electromotive force.

if you want to produce a charge on a glass surface rub it with silk.

Bye. Jasen

Yup, send that signal to a Xformer, full wave bridge and then to a decoupling cap!, you'll have 120 cycles of AC with 240 transitions! :)

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No, you have all 120 half cycles in phase instead of on both sides of the zero line (less two diode drops), but there are no transitions because the level never crosses the zero line when using full wave rectification.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

put the full wave into another xformer, you will get 120 cycles. using the cap, you would need a load R on the bridge side, i forgot about that.. common method of doing frequency doubling back in the old days.

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Real Programmers Do things like this.
http://webpages.charter.net/jamie_5