directional cables?

Herman

Thank you for coming up with an example that conclusively proves my point. That flow is a poor choice to describe what we call AC current.

Conventional wisdom says, as you and others have pointed out, that in order to have current flow you must have a complete path. That is true in DC and because of that it makes sense to use the word flow with DC. However, something different is happening with AC.

Nothing different happening with AC. At least not in this particular context, which I will remind you once again is audio cables. Specifically, analogue audio cables.

Yes, in order to have current flow you must have a complete path. But you're confusing having a complete path with a given electron flowing through the entire length of that path.

I have a battery. And a light bulb. I connect the light bulb to the battery with oh, let's say 100 feet of wire. The light bulb lights up. Ten seconds later, I disconnect the battery from the light bulb. The light goes out.

Was there ever any current flowing during that ten seconds? Of course there was.

However, the drift velocity of the electrons would have been slow enough that no given electron would have traveled more than a small fraction of the path.

Now let's connect the battery again but in the opposite polarity as before. Again, the bulb lights up. And ten seconds later I disconnect the battery.

As with before, no given electron ever travels more than a small fraction of the path. The only difference now is that they're flowing in the opposite direction from before.

Was there ever any current flowing during that ten seconds? Of course there was.

Now let's get fancy and hook up a switch between the battery and the wire that allows the battery's polarity to be switched. I flip the switch to one polarity for ten seconds, then the other polarity for ten seconds. Then back to the original polarity for ten seconds, and so on.

Was there ever any current flowing during those 10 second periods? Of course there was.

Now I do the same thing but at five second intervals. Was there current flowing? Yes. At one second intervals? Yes. At half second intervals? Yes. Quarter second? Eighth second? Sixteenth second? Yes. Yes. Yes.

Hook up a radio transmitter to a cable that is several wavelengths long but has no load, it is open. An EM wave will travel the length and reflect back to the source. Google "time domain reflectometer" for a practical application of this phenomenon.

I'm well aware of how TDR's work. In fact I've owned a couple in the past.

So why isn't that an issue with audio circuits. It would be if the cables were approaching a quarter wavelength but that would be several miles at audio frequencies so it doesn't cause any problems.

Right. But it IS audio circuits that we're discussing here. And my comments regarding current have all been within that context. And if you wish to address what I have said, then address it in the proper context.

I love it when my post gets a lot of responses. Thanks for the interesting comments and debate. TBromgard.

But it IS audio circuits that we're discussing here. And my comments regarding current have all been within that context. And if you wish to address what I have said, then address it in the proper context.

How pompous is that? You give me permission to address you only if I do so in a manner you approve? So radio transmitters used to explain AC are off limits but you want to use batteries and light bulbs? We're discussing AC, not batteries, which are DC. Audio and RF are both EM waves. I was trying to let you down easy with my transmitter example since you are obviously struggling with the EM wave concepts but now the gloves are off. Until you accept the fact that audio and RF are both EM waves that act the same way then you will never get it. I said it wasn't an issue with audio, not that it was fundamentally different. Let me know if you don't have one and I can loan you a good book on transmission line theory and EM waves.

The same principles apply only since the audio cable is such a small fraction of a wavelength the audio amplifier sees the open at the end of the cable as almost an open. Not quite an open but so close that for most discussions it can be considered one. However, there will be a teeny, tiny amount of current since the reflected impedance isn't infinitely high. If you had sensitive enough equipment you could measure the current. The transmitter example I gave was perfectly valid and you would know that if you understood the concepts.

Keeping with the context of this discussion, i.e. audio cables, all your source component does is simply apply a potential difference across its outputs. It doesn't apply an electromagnetic wave as without a completed circuit such as connecting a cable between the source component and the downstream component, there will be no current flow. And without current flow, there can be no magnetic field.

Again. Wrong. At what magic point does the cable get long enough that all of the sudden this magnetic field appears? It is always there but since the cable is so short the wave is very weak. If we happen to hit the right length of open ended speaker cable then the audio amp would see a short and there would be a lot of what we call alternating current. There is no separating the principles of AF from RF.

So it is indeed the "wiggling" that's causing the wave. No wiggling, no magnetic field. No magnetic field, no EM wave.

That is just plain wrong. You can't have an EM wave that does not have both an E and M field. The only difference in audio, RF, light or any other EM wave is the frequency. Light travels through a vacuum with no wiggling electrons yet it has a magnetic field. When I strike a match and it emits light are you saying the waves lack an M field since there is no current or are you are saying there is current in the match?

Yes, in order to have current flow you must have a complete path. But you're confusing having a complete path with a given electron flowing through the entire length of that path.

I just gave you a very specific example where you do not have to have a complete path for alternating current flow so now you have changed the definition of complete path. So now in your world open ended circuits are complete paths?

I give up. I can't hit a moving target. I'll leave you with a quote from the misconception link to show I'm not the only person who thinks like I do.

"What's the difference between AC and DC?

"AC" originally meant "Alternating Current", while D.C. meant "direct current". Over the years the meanings have changed. AC has come to mean "vibrating electrical signals." For example:

* AC is vibration, DC is flow
* AC is dynamics, DC is statics
* AC is like sound, DC is like wind
* AC is like ocean waves, DC is like rivers
* AC moves back and forth like a piston, DC moves continuously forward, like a drive belt.

If you hear people talking about "AC voltage", you need to realize that they are not saying "alternating current voltage". Instead they are saying "vibrating voltage".

With your permission I suggest you give that some thought. You probably think "AC voltage" is a good phrase along with AC current flow. Alternating current voltage? yea, that makes a lot of sense.

Good day.

Herman

How pompous is that? You give me permission to address you only if I do so in a manner you approve?

If I say something in a particular context, and you wish to take issue with it, then yes, I expect you to do so in the same context in which it was said.

So radio transmitters used to explain AC are off limits but you want to use batteries and light bulbs? We're discussing AC, not batteries, which are DC.

Yes, I know we are discussing AC, and yes, I know batteries are DC. But if you alternately change the battery's polarity with respect to the pair of wires feeding the light bulb, you end up with an alternating current. You know, AC.

This is fundamentally no different than your source component, preamplifier or amplifier, all of which are fed from a DC power source, and can even be powered from a battery, yet produce an AC signal at their outputs.

Are you going to argue that audio components are off limits because they use a DC power supply?

The battery in my example was nothing more than a power source. The end result was alternating current in the circuit attached to the power source.

The transmitter example I gave was perfectly valid and you would know that if you understood the concepts.

Your transmitter example was completely irrelevant in the context of what I had said and the argument I was making. We were discussing the appropriateness of using the terms "current" and "flow" as it related to AC. Specifically, in an audio system where the electrical wavelengths are vastly greater than line lengths.

I could have addressed your comments in their own context, but the two situations aren't quite the same and would have to be discussed rather differently than had previously been discussed and I saw that as a distraction which would just further confuse those who may be reading this trying to understand things.

If you can ONLY make your argument by invoking systems which are on the order of the wavelengths involved, then I can only say that your argument isn't holding water. If it did, then you could also make an argument in the context of a system which is a microscopic fraction of a wavelength.

So let's just stick to the original context in which this issue arose.

Again. Wrong. At what magic point does the cable get long enough that all of the sudden this magnetic field appears?

Even with just a short length of cable there will always be some amount of parasitic capacitance which means there will always be some current flow as a result and subsequently a magnetic field.

But talking about parasitics is just a distraction and I'm tired of distractions so let's get this back on track.

This all started with your saying the term "alternating current" made no sense.

I provided definitions of both "current" and "flow" from the Oxford English Dictionary which were quite in keeping with the notion of "alternating current."

Instead of addressing that, you instead went off on some other tangent.

So, no more distractions. Here they are again:

Flow:

"The action or fact of flowing ; movement in a current or stream ; an INSTANCE or MODE of this."

Current:

"That which runs or flows, a stream ; spec. a portion of a body of water, or of air, etc. MOVING IN A DEFINITE DIRECTION."

Again, whether the current is flowing in one direction during one half of the cycle, or in the opposite direction during the other half of the cycle, it is indeed moving in a definite direction. It is an instance of flow. It is a current. An alternating current.

Address this. No more distractions.