almarg
7,433 posts 08-23-2017 6:08pm
Hi Steve,
You raise good questions, which get into some complexities that are not obvious.
"The signal," and the energy that it conveys, is conducted through neither of the conductors. It is conducted in the form of an electromagnetic wave, which propagates at a substantial fraction of the speed of light in a vacuum, and propagates through the dielectric which surrounds the conductors. The exact propagation speed is dependent primarily on what is known as the "dielectric constant" of the particular insulation.
Putting aside reflection effects that can occur mainly at RF frequencies as a result of impedance mismatches, and assuming that the load is essentially resistive, that energy propagates in just one direction, from the source of the signal to the load. However, that propagation of the signal and its energy is intimately related to movement of electrons within both of the conductors, which takes place in both directions (the direction alternating in each of the two conductors, assuming we’re not dealing with DC), and which takes place at an ***extremely*** slow velocity that is referred to as "drift velocity." In the case of electrical signals that are conducted via wires (as opposed, for example, to being radiated through the air or a vacuum), the extremely slow movement of electrons within the conductors and the near light speed movement of the signal and its energy are intimately related, as I said, and one would not occur without the other.
A way to visualize it is that at the instant a signal voltage is applied to the source end of a cable, a **very** slow movement of electrons will occur into one of the two conductors at that end of the cable, and out of the other of the two conductors at that end of the cable, corresponding to the +/- polarity of the signal at that instant. At the other end of the cable, and at all points in between, there will be a similar slow movement of **different** electrons, with the response of those electrons being delayed from the response of the electrons at the source end of the cable by the amount of time it takes "the signal" to traverse the corresponding cable length (at near light speed).
What can be referred to as "the current," as opposed to "the signal," can be considered as corresponding to the number of electrons traversing a given cross-section of a conductor in a given amount of time. One ampere of current, for example, corresponds to one coulomb per second, where one coulomb corresponds to the amount of charge possessed by about 6.2 x 10^18 electrons.
So assuming that only two paths exist between the source and the load, namely the two conductors in a single cable, "the current" being conducted by both conductors in response to an applied signal is in fact identical, except that when it is moving in one direction in one conductor it is moving in the other direction in the other conductor. And in the case of audio signals, or any kind of signal other than DC, the directions in the two conductors alternate between each half-cycle of the waveform.
So with the slight possible exception I mentioned earlier about RFI/EMI pickup, in the case of a speaker cable the two conductors are of equal importance. In the case of a line-level analog interconnect, on the other hand, IMO the "ground" or "return" conductor should if anything be considered to be **more** important than the "signal" or "hot" conductor. The reason being that the characteristics of the return conductor may affect susceptibility to ground loop-related high frequency noise or low frequency hum, depending on the internal grounding configuration and other aspects of the designs of the particular components that are being connected.
So given the foregoing it hopefully becomes clear that your statement that...
... when I think about speaker cables, the "energy" in the signal conductor must be very different from the neutral side simply because by the time the signal gets through the speaker voice coil, most of it has been converted into the movement of the driver, so the neutral must be quite different - doesn’t it? ... is not a correct statement because the transfer of energy to the load goes hand-in-hand with current (movement of charge carriers, i.e., electrons) in **both** conductors. With that movement being equally important in the two conductors, and (putting aside the possible ground loop and RFI/EMI effects I’ve mentioned) being identical in the two conductors aside from being in opposite directions at any instant of time.
Hopefully that clarifies more than it confuses :-)
Best regards,
-- Al
Al, Great post! Jim . |
almarg
7,435 posts 08-24-2017 3:12pm
Jim (Jea48), I’m not sure if your most recent post is suggesting that I try to explain why Geoff’s comment is incorrect, or that I refrain from doing so to avoid having this heretofore constructive thread go downhill the way the recent thread on wire directionality has. But I’ll assume the former, perhaps incorrectly. Al, For the latter. I am glad you answered Geoff’s post though. Jim |
@kijanki,
Thank you for the response.
Jim
|
kijanki
3,274 posts 08-24-2017 6:39pm
Dielectric constant of Teflon is about 2. Vacuum has dielectric constant of 1.
Yes, Teflon will slow down electromagnetic wave. Insulator will slow down electromagnetic wave by amount based on its ability to store energy - Permittivity. Dielectric constant is just relative Permittivity. This speed of electromagnetic wave thru typical insulated wire is about 60% of the speed of light in the vacuum. For typical cable it comes to about 5ns/m and it is exactly true for cat5 cable. There is no different electromagnetic wave for audio signals and other signals. kijanki, Can the type of dielectric used cause distortion of an analog signal as it travels through an interconnect? What frequencies, would you say, are affected the most? Example PVC vs Teflon? Tough question.... Can it be measured? Jim |
Al (almarg) and kijanki,
I would trust your "expectation bias" over some others so called facts any day.
Thank you both for your contributions to this audio forum. I never stop learning from what the two of you have to say. Sometimes I may not fully understand, but eventually it sinks in.
Thanks again,
Jim
|
@almarg, AC transmission using wire conductors. Al, Could you please explain in more detail the relationship of the electromagnetic wave, that travels in the space outside of the conductor, (At near the speed of light), and the "current" that travels very slowly slightly vibrating back and forth at 60Hz in the conductor. From what I understand the movement of the current in the conductor is quite slow.... Correct? The electromagnetic wave is caused by the applied source voltage and the "current", "charge", in the conductor? (Amount of current in the closed circuit determined by the resistance of the connected load. I = E/R)..... Correct? Am I correct in saying you can’t have the electromagnetic wave without having current? Install an on/off switch in series in the circuit. Close the switch the current passes through the switch contacts through the load and back to source.... Correct? The bigger the load, the more current in the conductor. The more current in the conductor the larger the electromagnet wave.... Correct? And of course the conductor, wire, must have a current, ampere rating, to safely carry the current in the wire so the wire will not overheat.
IF the wire is too small to handle the amount of current in the wire is it the current that causes the wire to overheat or is it the energy of the electromagnetic wave? Please explain in detail.
.
Not to confuse things, if only a voltage, (potential), is present, an electromagnet field will exist outside of the conductor/s without there being current... Correct?
. I know it is the energy, from the electromagnetic wave, that makes a heating element heat up and gives off its’ heat into the surrounding air around it. It is not the "current" directly causing the resistance element to heat up.... Correct?
I know the amount of energy consumed,(in watts), by the resistance element is determined by the source voltage and the resistance, in ohms, of the resistance element. E / R = I and we know the current..... Correct? The Fuse..... E x I = P E = voltage I = Current, amps
P = power, energy, measured in, watts, VA
A fuse rated at 2 amps with a maximum voltage rating of 250V. herman said it is the energy of the electromagnetic wave passing on the outside of the fuse element link that causes it to melt and blow open when the fuse is overloaded.
OK Isn’t the size, (for lack of a better word), of the electromagnetic wave energy determined by the applied source voltage and the current in a closed circuit? E x I = P. Is not P the energy of the electromagnetic wave? So say the load is 150 watts and a 2 amp 250V fuse is used to protect the load. The FLA of the 150 watt load is, 150W/120V = 1.25 amps. Here is where I get hung up. As you know a 2 amp 250V fuse can be used for any voltage 250V or less. It could be used where the voltage is 24V. The ampere rating of the fuse is still 2 amps. So to me the current has to be some component that causes the fuse to blow when the current that passes through the fuse link and exceeds 2 amps in the time curve set by the fuse manufacture. NOTE I did not say current flow.
WOW,... I know,..... I sure have a lot of questions on my mind. Blame herman.
Very best regards, Jim |
Al, (almarg), Thank you for your responses to my questions. ... if only a voltage, (potential), is present, an electromagnet field will exist outside of the conductor/s without there being current... Correct? I’m not 100% certain, but I believe in that situation an electric field would be present, but not a magnetic field. I would agree, it is an electric field not a magnetic field. . Since the amount of energy that is absorbed from the electromagnetic wave by the conductor in the fuse and converted into heat (causing it to blow if excessive) is proportional to both the energy that is being conveyed by that wave and to "the current," it is reasonable (and of course far more practical) to analyze the situation in terms of amperes and ohms, rather than in terms of joules (a unit of energy) and Poynting Vectors.
And correspondingly, since in the case of electrical signals (or power) being conducted via wires the slow moving "current" and the very fast moving electromagnetic wave go hand-in-hand (as I’ve explained), IMO it would be meaningless to think of one but not the other as being the cause of the fuse blowing. Your second paragraph has to be the logical case. And not just for the "why" the fuse blows. The electrical energy will be greater at 120V than at 24V for a circuit using the same 2 amp fuse for overcurrent protection. 120V x 2A = 240 watts 24V x 2A = 48 watts 240V x 2A = 480 watts Am I correct in assuming watts is a measurement of electrical energy? Jim . |
Al, Thanks again for your response. Thanks, Jim. Regarding...
Am I correct in assuming watts is a measurement of electrical energy? Watts is a unit of power, as you of course realize. Power is a quantity that is defined at a specific instant of time, although its average value over some interval of time can of course be calculated. Energy is defined as the product (multiplication) of power and time, and can be expressed as some number of joules, as well as in various other units. Well I knew watts is a unit of power and I somewhat understood energy and joules. But I guess I didn’t understand the real differences between the two. I do have a better understanding now thanks to you Al. . The electrical energy will be greater at 120V than at 24V for a circuit using the same 2 amp fuse for overcurrent protection.
120V x 2A = 240 watts
24V x 2A = 48 watts
240V x 2A = 480 watts The power and the energy being conveyed to the load will of course be much greater in the 120 and 240 volt cases than in the 24 volt case. But as I’m sure you realize but others may not, the only voltage that the fuse "knows about" is the one that appears between its two terminals, which when it is not blown corresponds to the amount of current it is conducting times its resistance. In the case of audio equipment operating normally that voltage will typically be a small fraction of a volt.
Quote: "But as I’m sure you realize but others may not, the only voltage that the fuse "knows about" is the one that appears between its two terminals, which when it is not blown corresponds to the amount of current it is conducting times its resistance." " times its resistance." I have not ever heard it explained that way before. I honestly have never measured a voltage across the end caps or blades of a good fuse. A blown fuse on the other hand yes, as you stated. I have measured a slight voltage drop across the fuse holder clips, mostly cartridge fuses. A VD across the fuse holder clips indicates poor contact pressure and or corrosion, poor surface area between the fuse caps and fuse holder clips. The only fuse I have on hand is a 4 amp slow blow fuse. I have an older model Fluke 87 True RMS multimeter and I checked for resistance across the fuse link end caps. With the meter set on ohms auto first touching the two probes together the meter reads 000.01 ohm. I got the same exact reading checking the fuse. LOL, I even reversed the fuse and got the same reading. (You know who that was for) I have read posts of guys that buy audio grade fuses that say they do indeed measure a resistance across the fuse link end caps. What you said above does make sense though. I have a good basic understanding how the electromagnetic wave thingy works, I just need learn the lingo better how to express it. Me thinks when talking about electrical power issues and electrical safety codes, like NEC, I will stick with the old school way I was taught and have a good understanding of. Besides that is what the majority of people understand. Especially electricians. As for ICs and speaker cables the old school theory just doesn’t fit the reality of how the audio signal travels from the source to the load. Thanks again Al for all your help, Jim . |
Correction: In my post dated 09-01-2017 8:33pm The only fuse I have on hand is a 4 amp slow blow fuse. I have an older model Fluke 87 True RMS multimeter and I checked for resistance across the fuse link end caps.
With the meter set on ohms auto first touching the two probes together the meter reads 000.01 ohm. That should read, meter reads 000.1 ohm. . |
@kijanki, Thank you for your informative response.
From what I understand the movement of the current in the conductor is quite slow.... Correct?
Electric
current is a flow of electric charge and not the flow of electrons.
(In fluids electric charge is carried by ions and not the electrons).
Number of electrons crossing given point defines amount of electric
charge (current) passing. Motion of electric charge is usually
explained as a row of stacked balls in the tube - when you push them
slowly they will move slowly but when you hit the first one with a
hammer the last one will respond instantly - that's the speed of
electric current (charge). Of course there is plenty of space between
electrons but "stacking" is not physical but electrical (electric
charge).
Quote from link below.
Electric current is not a flow of energy; it's a flow of charge. Charge
and energy are two very different things. To separate them in
your mind, see this
list of differences.
An electric current is a flowing motion of charged particles, and the
particles do not carry energy along with them as they move. A current is
defined as a flow of charge by I=Q/T; amperes are coulombs of charge
flowing per unit time. The term "Electric Current" means the same thing
as "charge flow." Electric current is a very slow flow of charges,
while energy flows fast. Also, during AC alternating current the
charges
move slightly back and forth while the energy moves rapidly
forward.
Electric energy is quite different than charge. The energy
traveling across an electric current is made up of waves in
electromagnetic fields and it moves VERY rapidly. Electric energy moves
at a completely different speed than electric current, and obviously they
are two different things flowing in wires at the same time. Unless we
realize that two different things are flowing, we won't understand how
circuits work. Indeed, if we believe in a single flowing "electricity,"
we will have little grasp of basic electrical
science.
In an electric circuit, the path of the electric charges is circular,
while the path of the energy is not. A battery can send electric energy
to a light bulb, and the bulb changes electrical energy into light. The
energy does not flow back to the battery again. At the same time,
the electric current is different; it is a very slow circular flow, and
the electric charges flow through the light bulb filament and all of them
flow back out again. They return to the battery.
The term "Electric Current" means the same thing
as "charge flow." Electric current is a very slow flow of charges,
while energy flows fast. Also, during AC alternating current the
charges
move slightly back and forth while the energy moves rapidly
forward.
The
energy does not flow back to the battery again. At the same time,
the electric current is different; it is a very slow circular flow, and
the electric charges flow through the light bulb filament and all of them
flow back out again. They return to the battery.
http://amasci.com/miscon/eleca.html#cflowAfter reading your post I went back and checked again what I had read. Then I clicked on the blue high lighted "slow" word. And this came up.
The quick answer
Inside the wires, the "something" moves very, very slowly, almost as
slowly as the minute hand on a clock. Electric current is like slowly
flowing water inside a hose. Very slow, so perhaps a flow of
syrup. Even maple syrup moves too fast, so that's not a good analogy.
Electric charges typically flow as slowly as a river of warm putty. And
in AC
circuits, the moving charges don't move forward at all, instead they sit
in one place and vibrate. Energy can only flow rapidly in an electric
circuit because metals are already filled with this "putty." If we push
on one end of a column of putty, the far end moves almost instantly. Energy
flows fast, yet an electric current is a very slow flow.
Then,
The complicated answer
Within all metals there is a substance which can move. This stuff has
several different names: the Sea of Charge, or the Electron Sea, or the
Electron Gas, or "charge." We often call it "electricity," and state
that electric currents are flows of electricity. Calling it
"electricity" can be misleading because many people believe that
electricity is a form of energy, yet charge is not energy, and currents
are not flows of energy. Also it can be misleading because the Sea of
Charge
exists within in all metal objects, all the time, even when the metal
hasn't been made into a wire and is not part of an electric device. If the
Electron Sea is "electricity," then we must say that all metals are
always full of electricity, and that batteries are simply
electricity-pumps. Better to call it by the name "charge-sea," and avoid
the misleading word "electricity" entirely.
During an electric current, the metal wire stays still and the sea of
charge flows along through it. When the flashlight switch is turned off
and the lightbulb goes dark, the charge-sea stops moving forward. Even
though it stops moving, the charge-sea is still inside of that wire. If
the flashlight is again turned on, but then two light bulbs are connected
in
parallel instead of one, the electric current will have twice
as large a
value, and twice as much light will be created. And most important, the
charge-sea within the battery's wires will flow twice as fast. In other
words, the speed of the charges is proportional to the value of
electric current; small current means slow charge-flow, large
current means
high speed. Zero current means the charges have stopped in place. Note
however
that an electric current does not have just one speed within any circuit.
Charges speed up whenever they flow into a thinner wire. The high current
in a large flash-lantern's lightbulb will be much faster than the same
current in the other conductors in the lantern. Even though an electric
current is a very slow flow of charges, we can't know the actual speed of
flow unless first we know the thickness of the wires, as well as the
*value* (the amperes) of the current in the wires.
Quote:
"In other
words, the speed of the charges is proportional to the value of
electric current; small current means slow charge-flow, large
current means
high speed. Zero current means the charges have stopped in place. Note
however
that an electric current does not have just one speed within any circuit.
Charges speed up whenever they flow into a thinner wire. The high current
in a large flash-lantern's lightbulb will be much faster than the same
current in the other conductors in the lantern. Even though an electric
current is a very slow flow of charges, we can't know the actual speed of
flow unless first we know the thickness of the wires, as well as the
*value* (the amperes) of the current in the wires. " And then he says,
The speed of electric current
Since nothing visibly moves when the charge-sea flows, we cannot measure
the speed of its flow by eye. Instead we do it by making some
assumptions and doing a calculation. Let's say we have an electric
current in normal lamp cord connected to bright light bulb. The electric
current works out to be a flow of approximatly 3 inches per hour. Very
slow!
http://amasci.com/miscon/speed.htmlWow! I'll have to reread it again tomorrow. But I think he is saying the same thing you said. At least some parts of what he is saying. But not others? Thanks again for your response, Jim |
almarg 7,451 posts 09-02-2017 1:14pm I don’t know what the gauge of the leads is, but given that the total length of the two leads is about 8 feet I suspect the lead resistance is a significant contributor to the 0.1 ohms, together with round-off due to the limited resolution. I got the same reading from my Fluke 87. Regarding fuse resistance, you might find the information on page 2 of this Littelfuse datasheet to be of interest. For the 4 amp 250 volt slow blow 6.3 x 32 mm glass fuse which is among the many listed, the "cold" resistance (meaning the resistance with negligible current being conducted) is indicated as 0.0311 ohms. So for a design which puts say half the rated max current through it the voltage drop would be a bit more than 0.06 volts. Al, I will check out the link you provided. So for a design which puts say half the rated max current through it the voltage drop would be a bit more than 0.06 volts. There’s that current again..... Just a guess the more current, the more heat produced by the energy the load is consuming, the more the resistance of the fuse the greater the VD. Correct? Or is it the more energy the load is consuming the greater the current. Which came first the chicken or the egg? At any rate my understanding, it is, the energy the load is consuming, that if it, increases above the rating of the fuse, (given by the manufacture in amperes), the fuse link will melt breaking the circuit. IT IS the energy that melts the link, not the current. Sound about right? I hope. I am still confused on the discussion of current in a closed circuit. Here is part of a response herman posted in response to a post of mine. herman
1,950 posts 05-26-2010 10:21pm
Jea, There are positive and negative charges and they are what they are. They do not change from positive to negative. In the case of a wire there are negative charges in motion but in some mediums there are + charges in motion and in some there are both.
So it isn’t + 0 - 0 + 0 - as in the charges are changing polarity it is L 0 R 0 L 0 as in the negative charges are vibrating left and right around a zero point.
If electric current is the movement of charge what is wrong with using the word current in place of the word charge? Any place you see "current" you can substitute "movement of charge." If you say movement of current you are saying movement of movement of charge. It is redundant.
Look at it this way. In order for something to move it must exist. Current is not a thing or a form of energy, it is a word that describes movement. If water stops flowing the water is still there but there is no current. Did the current just disappear? No, it never existed, it is a concept, not a thing.
With the load consuming power from the supplying alternating voltage source explain the process movement of current to the load.
Thank you, thank you, thank you for asking. That question is a perfect example of why "alternating current flow" is a very bad description of what is going on.
In a nutshell AC current does not move or flow to the load.. That is the very heart of my debate with simply_q.
As stated above current does not move. Current means something is moving. If we switch to charge instead of current then those don’t move to the load either. The charges in an AC circuit merely sit there and vibrate.
Power isn’t moving to the load either. Power is the rate at which we transfer energy. Power is not a thing, it is not energy, it cannot be moved or consumed.
So what’s moving from the source to the load? Energy. A wave of electromagnetic energy moves down the wire and the energy in it is transferred to the load. Charges are vibrating everywhere around the path but energy is flowing in one direction...source to load. It is converted into another form of energy like heat or light, or motion, or it is launched into space if the load is an antenna. Quote: As stated above current does not move. Current means something is moving. If we switch to charge instead of current then those don’t move to the load either. The charges in an AC circuit merely sit there and vibrate. Later on down the page herman posted a responded again to a post of mine. If you say the AC fuse blew because there was too much current flowing through it everybody nods in agreement even though that isn’t true. If you say the wire in the fuse melted because it got too hot after absorbing energy from the electromagnetic wave people look at you like you are insane and want to argue that vibrating electrons constitute current flow.
These really are confusing topics as we have discovered in this thread. People frequently confuse energy and power. Most people think current is a thing when it is not. It was pounded into our heads that current flow is the same everywhere in a series circuit so we incorrectly think charges are flowing through components in an AC circuit. Yea I know, I sound like a broken record, but you asked/
The problem is there are many technically incorrect phrases that are so ingrained that we can’t seem to get away from them. Everybody says it including me but power can’t really be consumed because it isn’t a thing, it is the rate at which energy flows, but if you say an amplifier consumes 100 watts of power everybody nods in agreement. If you correctly say energy flows into that amp at the rate of 100 Joules per second they look at you like you are nuts. https://forum.audiogon.com/discussions/directional-cables?page=3Jim |
Al (almarg), - What is the stuff that flows through a light bulb and comes back out again through the other wire?
The answer to question #1 is ELECTRIC CHARGE. Charge is a "stuff" that flows through lightbulbs, and it flows around a circuit. Normally no charge is lost during the operation of a circuit, and no charge is gained. Also, charge flows very slowly, and it can even stop flowing and just sit there inside the wires. In an AC circuit, charge does not flow forwards at all, instead it sits in one place and wiggles forwards and back.
http://amasci.com/elect/elefaq1.html#aelistIs this guy wrong? regards, Jim |
