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#136747 - 05/04/03 04:51 AM Superimposed Currents
Belgian Offline
Member

Registered: 10/10/02
Posts: 177
Loc: antwerp
Can anybody explain what happens on an atomic scale when you superimpose currents of different frequencies? Maybe C-H?

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#136748 - 05/07/03 10:35 AM Re: Superimposed Currents
Belgian Offline
Member

Registered: 10/10/02
Posts: 177
Loc: antwerp
Y does nobody want to explain it to me?

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#136749 - 05/07/03 05:58 PM Re: Superimposed Currents
Hutch Offline
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Registered: 05/27/02
Posts: 383
Loc: South Oxfordshire, UK
At the atomic scale... Down at this level the distinction between matter and energy starts to get blurred. How far down the atomic scale do you wish to go? On a waveform basis I expect the electon to exibit the equivalence of white noise (every frequency in the universe) with a resultant current of zero. Carefully select your frequences though and it's a different matter. I feel some Fourier analysis coming on.

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#136750 - 05/08/03 02:07 PM Re: Superimposed Currents
Belgian Offline
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Registered: 10/10/02
Posts: 177
Loc: antwerp
I was just wondering if there are electrons going in opposite directions at the same time and can this affect the capacity of the load on the wire?

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#136751 - 05/08/03 06:29 PM Re: Superimposed Currents
Hutch Offline
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Registered: 05/27/02
Posts: 383
Loc: South Oxfordshire, UK
Belgium you are quite right, I think C-H's input maybe required here to deal with the behaviour of electrons outside of the nucleus with all of their orbitals and spin. I would think though on a Newtonian scale that as current (the movement of electrons) is caused by an external field, expressed as a voltage, that the net current induced an instant of time is a function of the resultant frequency product at that instant and that all electrons subject to that field would behave in an identical manner.

Now back down at an atomic level where electrons exist or not, at any instant, in wells of exclusive probability – they could theoretically be doing anything at an instance without any external influence except for the background energy above absolute zero.

I think that I’m about to fall off the end of my limb! C-H…

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#136752 - 05/09/03 09:58 AM Re: Superimposed Currents
C-H Offline

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Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
Hey, guys, I'm not a physicist. Fourier analysis - shrugs...

I think this really is Paul Coxwells field, as he knows telephone systems, where you have several frequencies. (From your voice!) Just to hand over the hot potato...

I don't know the answer, but as the question is interesting, let's see if we can reason us to a result:

The wave in an electrical conductor is moving much faster than the electrons. You can send a wave down a conductor almost without moving the electrons at all. A socket outlet where you have not plugged anything in is an example.

The wave which is easiest to illustrate this with is perhaps the wave among the spectators on a stadion. People don't even move in the same direction as the wave. They sit down and stand up waving, whereas the wave moves sideways. In this case there are only two states, standing up or sitting down. If we had more states, like "standing with hands down", we could send two waves with different speeds at the same time. When there is no wave passing, people sit. When one wave pass, people stand without waving. If both waves pass at the same time, people will stand up and raise their hands. You won't see spectators standing up with their hands above their heads mixed with spectators sitting down.

Back to our socket outlet: Let's say we have wired it up to a 50 Hz and a 60Hz generator in series. Are we going to get heating in the wires because of the different frequencies? Not as long as the circuit is open. Otherwise it would violate the basic principle that electricity needs a closed circuit to flow.

(I don't think this holds true if we have very high frequencies ( kHz ), since the wires will essentially have become a radio antenna.)

In reality, what we have done by superimposing the two frequencies is to create a new waveform. What happens if we plug a resistor into the socket? It will heat up proportionally to the average voltage of the supplying source. We could just as well have heated it with a DC current with the same voltage. This does not hold true for other components, like capacitors.

But, as wires are essentially resistors, the heating of the wires will be the same as if we had used them for a DC current. From this, I conclude that superimposing currents of different frequencies does not case more heating of the wires. It's only the current that matters.

This would indicate that the electrons aren't going in both directions, but rather in just one direction. The atoms in a metal share a common electron cloud, which hold the atoms toghether and makes metals good conductors. (Other materials have ionic or covalent bonds, where the atoms share individual electrons.)

Atoms move at random. (This movement is how heat is stored, and what we call temperature is really how much the atoms move.) It is a reasonable assumption that the cloud of electrons move or change properties at random too, totalling zero current. That is just what Hutch wrote in his first reply.

Superimposing a current with any type of waveform on the random movement simply means that the movement of the cloud will follow the waveform, in addition to the random pattern. Superimposing two currents of different frequency will not cause electrons to go in different directions (apart from any random movement) at the same time since the cloud follows the resulting total waveform. There will not be two separate waves that propagate via different electrons.

Well, that's my take on it. I really hope someone steps in and corrects me now

[This message has been edited by C-H (edited 05-10-2003).]

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#136753 - 05/10/03 03:17 PM Re: Superimposed Currents
Belgian Offline
Member

Registered: 10/10/02
Posts: 177
Loc: antwerp
Wow! C-H, I knew that if I asked you , you would have SOME explanation! Can you clarify some things:
You said "The wave in an electrical conductor is moving much faster than the electrons" How so? Sorry for my ignorance, but what is a wave, then?
"Superimposing two currents of different frequency will not cause electrons to go in different directions ... at the same time since the cloud follows the resulting total waveform. There will not be two separate waves that propagate via different electrons." You say that that the cloud follows the resulting total wave form. Then how are seperate wave signals sent on existing electrical networks?

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#136754 - 05/11/03 01:42 AM Re: Superimposed Currents
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Yes, in telephone and other communications work we're frequently concerned with having many different frequencies transmitted simultaneously, from a single telephone carrying about 300 to 3400Hz up to wideband carrier systems with a bandwidth of many megahertz.

Differential delay is a major concern in some of these networks, where the reactive components of the lines result in different frequencies taking different amounts of time to propagate through the system. In a TV transmission line, for example, an uncorrected delay can result in the color (on a sub-carrier at 3.58 or 4.43MHz) being displaced slightly from the corresponding luminance information.

I have to confess, however, that when it comes down to the level of what's happening to the individual electrons in the copper, it's getting into the realm of particle physics and a little outside my province.

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#136755 - 05/12/03 09:24 AM Re: Superimposed Currents
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
 Quote:

You said "The wave in an electrical conductor is moving much faster than the electrons" How so? Sorry for my ignorance, but what is a wave, then?


A wave is information that is moving forward. Let's say we fill peas in a pipe, one after another. Put the pipe on a table, with both ends open. Push the first pea on one side: This will push the next pea, which pushes the next and so on until the last pea moves. The individual peas have just moved a little, but nevertheless we have transferred the movement all the way to the other end of the pipe. As you can see, the speed of the individual peas is lower than the speed of the pulse (wave).

The same phenomenon can be observed if you stand by the sea: The waves are moving much faster towards the shore than the water itself: You see floating object go up and down, not just rushing towards the shore.

In some cases the wave is in fact moving slower than the particles are. If you are running, the noise you make will always preceed you because the sound (wave) is faster than you. But if you fly an airplane faster than the speed of sound, the molecules in the air will be moving faster than the wave. The result is that the air ahead of the plane are has no idea that the the plane is approaching. Therefore nobody can hear it, until the plane reaches them. (Ok, in reality the air immediately around the plane is moving above the speed of sound relative the surroundings, but below the speed of sound relative the plane. Therefore there is a shockwave immediately in front of the plane where this air collides with the still air)

 Quote:

"Superimposing two currents of different frequency will not cause electrons to go in different directions ... at the same time since the cloud follows the resulting total waveform. There will not be two separate waves that propagate via different electrons." You say that that the cloud follows the resulting total wave form. Then how are seperate wave signals sent on existing electrical networks?


I'll have to think before I answer that one. I'll be back...

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#136756 - 05/13/03 02:21 AM Re: Superimposed Currents
Belgian Offline
Member

Registered: 10/10/02
Posts: 177
Loc: antwerp
Thank you, C-H for your explanations.
I'll try to formulate my question in a different way so that you understand exactly what's bothering me.

When we talk about Frequency in a electrical net (50 or 60 Hz), it is represented in sinusoidal form. So my reasoning is that it can be called a wave, right? Now, this wave, we know in which way that it's propagated. With the electrons going back and forth, which is also the electrical current, right? (Please correct me if I'm wrong.)
Now, my question is what is a simple Radio Wave. How is it propagated in the air or in a cable? Is it also with a electrical current(however small it might be)? If yes, then what happens when you have 2 superimposed waves? How will they keep their identity and how come they don't disturb one to the other?
I hope that my question is clearer. I also hope that I'm not way off, but if yes then I would appreciate if you could explain.

[This message has been edited by Belgian (edited 05-13-2003).]

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