True but pointless. We know what we mean. Even 'current' is a borrowed term used as an analogy as is 'potential' or even 'pressure'. If we have voltage surely we should only speak of amperage.
N
Oh, I agree. I just think it helps to be a bit patient. Not that I'm all that good at patience, myself. But we should try. We have all been rookies, once or twice.
-- Al Brennan "If you only knew the magnificence of the 3, 6 and 9, then you would have a key to the universe." Nicola Tesla
That's going a bit far. "Meaningless" means no meaning, and that is not really an accurate description for the terms AC and DC. They have a pretty well understood meaning, despite some suggestions in this thread.
"quotes with no meaning, are meaningless" - Kevin Aylward
Kevin Aylward snipped-for-privacy@anasoft.co.uk
Since we are quibbling her on terms, lets get this bit straight shall we.
"Current flow" is wrong. Its simply "current" or "charge flow". "Current" already contains the notion of "flow".
Kevin Aylward snipped-for-privacy@anasoft.co.uk
Actually, the ones with the requirements, assertions, and definitions are codes and organizations such as the NEC and the IEEE, and the bothersome universities that teach the stuff.
On this point:
You are talking about transients, and if you intend for the questions to be rhetorical, then I think you should demonstrate some expertise in the subject matter that shows why the questions' answers must be obvious. I don't think they are, so I will answer the questions:
The behavior of the flashlight in your example is neither AC nor DC, it is transient. The first case is the instantaneous step function caused by the closing of a source to a circuit. The second case is a long-term curved ramp caused by the decay of a voltage source. AC and DC analyses are steady-state. AC analysis will never apply to the example. DC analysis must be performed prior to the transient analysis in order to provide a steady state model for the application of time-sensitive mathematics.
There is quite a bit of information available on the web about circuit analysis. Your curiosity is to be commended; you might consider a web crawling adventure, or even an education in the field.
And hey operator jay, what do you operate? Not electrical substations, I wouldn't guess.
-- Al Brennan "If you only knew the magnificence of the 3, 6 and 9, then you would have a key to the universe." Nicola Tesla
No, both do not - only one of the 1 volt/.6 volt examples given has an _alternating_ direction component - both examples do have a _variation_ in their magnitude component. ( This is not a new discussion - and all of the dozen or so engineering and physics texts and training manuals I have researched on the matter adhere to the "alternating is reversing" definition of AC. It has been custom and practice for at least 40 years.)
1) the 1 volt dc with the .6 sine variation does not alternate its direction of flow. Its flow only varies in the magnitude of the charge flowing always in one direction. It has no alternating current ( i.e, it has no regularly reversing, i.e. _alternating_, charge flow direction) 2) the 1 volt sinewave with the .6 volt dc does reverse charge flow direction. It is alternating in its flow direction. It also varies in its magnitude.The direction of the description vector must alternate in order to have Alternating Current. If it does not change direction but only varies in magnitude, the descriptive vector is not alternating, it is merely varying in magnitude.
3) Impedance laws apply equally to varying DC and to AC.
Interesting! I thought John's response to the op was called for. The OP is going to get himself into trouble with the attitutde he's exhibited. In my opinion, John saw through the BS and called a spade a spade. I don't know whether the OP got it or not - but John made it clear that the BS wasn't fooling anybody.
I'll have to go back and read it again in light of your post.
Ed
'Alternating' is not the same as 'altering'. "Alternating current" is an electrical current where the magnitude and *direction* [emphasis added] varies cyclically.
One may 'alter' the magnitude of a DC current without it becoming 'alternating current'
daestrom
It is true by most definitions of 'Alternating Current'.
'Alternating' means both magnitude and direction vary over time. A current that varies in magnitude but not direction is not 'alternating'.
Only by your apparent definition. But your definition does not agree with the established industry.
By adding a capacitor in series, you have altered the circuit. The capacitor filters out the DC component of a the original varying DC voltage applied. The capacitor has a varying DC voltage across it, but it never changes polarity (you can use an electrolytic capacitor that is polarity sensitive without damage).
The current through the resulting series circuit *does* alternate in magnitude and *direction*, even though the voltage applied to the circuit varies in magnitude only. So yes, the 'AC came from somewhere'. But that doesn't mean the applied voltage is AC. Such logic is flawed. There is no 'law of conservation of AC' that says it can't be 'generated by the capacitor'.
Repeating yourself doesn't make you correct.
daestrom
Then you'll have a very difficult time explaining now a transistor amplifier works if it uses AC coupling that involves capacitors.
Which industry? You can't do AC circuit analysis with any other definition.
Capacitors don't generate voltage or current. The circuit alteration merely demonstrates that the voltage and current on one side meets all of your requirements, while the identical charge flow on the other side does not, which indicates a flaw in your specification.
Yes, which leaves the AC that was there all along. It's AC after, and it was AC before. If you do circuit analysis the treatment is exactly the same on both sides of the capacitor.
Exactly. Yet there *is* current through the capacitor, which only passes AC. That AC current isn't generated inside that capacitor. It comes out one side, so it *had* to be coming in the other side.
That's hilarious. DC applied to a capacitor generates AC????
I don't think so.
Won't help your point either. And it makes no difference how many places you find it ill defined either.
-- Floyd L. Davidson Ukpeagvik (Barrow, Alaska) floyd@barrow.com
You were doing pretty good up to that point.
No. But that doesn't mean there is never any AC present in the circuit.
It happens that with a battery powered flashlight that is rare (but predictable too), and of no consequence whatever. It can be ignored in design and operation of the flashlight. But that doesn't mean there is never any AC in the circuit, or that there are no circuits where it is significant.
Every time you flip the switch on or off, there is AC in that circuit.
You can probably prove it too, relatively easy. Tune an AM receiver to a frequency where no station is being received, and hold the flashlight up close to the antenna. Flip it on and off a few times. I suspect, though I haven't actually tried this, that you'll hear a pop in the radio's speaker almost every time you flip the switch. That is because some of the AC produced by flipping that switch is RF.
It's been 24 hours of daylight for quite some time now. The sun hasn't actually gone down for a month (May 10th), but of course we had 24 hours of light long before that. The next time it gets below the horizon will be August 1, and it will be late August before it gets "dark".
The temperature is 30F right now, with a reported 18 mph wind and fog. It was gusting up to 30 mph last night. It probably won't get much warmer than maybe 36F today.
That is actually very comfortable weather, mostly because it is unlikely to rain. I hate getting wet... :-)
-- Floyd L. Davidson Ukpeagvik (Barrow, Alaska) floyd@barrow.com
Given the significant experience of several people involved in this discussion, and the wide variety of interpretations they are giving to those terms, it would seem that just about the
*only* thing one could positively take away from this particular discussion is that, as Don says, those terms are meaningless.-- Floyd L. Davidson Ukpeagvik (Barrow, Alaska) floyd@barrow.com
-- No. With the exception of electroscopes and such like, all voltmeters are really ammmeters and what was being referred to was really a galvanometer
Item 3 is correct. That is because "varying DC" *is* AC.
It is AC even if the axis is shifted far enough to avoid polarity reversals relative only to some specifically defined 0 current.
The reversals are relative... to the steady state condition, not to some magical 0 current where supposedly no electrons are flowing.
Otherwise, instead of two types, you are dividing circuit analysis into three types, two of which are identical in all significant respects other than an arbitrary definition that is meaningless.
It makes no sense to say that "Impedance laws apply equally" and then claim that the two are not identical.
-- Floyd L. Davidson Ukpeagvik (Barrow, Alaska) floyd@barrow.com
-- Yes, it is. If you have proof, instead of just a statement to the effect that it isn't, I'd love to see it.
Strictly speaking, I believe the reactance (part of impedance) equations apply to any variation in current magnitude. Their appropriate application does not in any way require reversing the charge.
1) I think one needs to define the term "alternating current" by its phenomena rather than define it by what applies to "AC". In other words, define AC as alternating current -rather than defining AC as "anything requiring an impedance calculation because of its magnitude variation". ( OK, all scientific definitions require definitions in terms of other defined concepts; thus voltage and charge are defined in terms of force. And yes, any phenomena in its purest defined form uses the fewest of the core units, and only the core units, of the measuring system. And yes, since, unlike in the British ft-sec-lb system, force is not a core unit of the metric kg-sec-m system, one cannot be as "pure" in the metric system with many definitions as one can be in the British system, "decile" convenience notwithstanding)2) There are two phenomena and two descriptive words if one uses the mathematical description of the changes associated with current: changes in current _direction_ and changes in current _magnitude_.
There are three (or more) phenomena if one uses only the two descriptive terms _AC_ and _DC_, well evidenced in this thread: changes in direction and magnitude, changes in magnitude only, or no changes in either magnitude or direction. Three phenomena defined using only two words for those three cannot be specific and exclusive enough for a rigorous definition. The middle condition, the overlap as it were, ends up wanting.
3) In the definition approach to a phenomena, one deals with the descriptive term and the phenomena itself and ignores the present attached effects. Once the definition is had, then the phenomena's interaction with other phenomena can be determined. Yes, having such rigor in a definition can be more complicated in its application.In the application approach to defining a phenomena, one defines by addressing what equations, etc., apply to the condition. In this approach, you end up in circular arguments, chasing your tail. Something always will not fit. Like changes in magnitude without changes in direction.
is
in
i.e.
varying
-- No, if the direction of charge flow alternates between two states, then it's Alternating Current.
Do a reality check on what you are saying! Capacitors do *not* generate AC, and when the rest of your theory depends on the idea that they do, you've made a mistake.
You haven't drawn the schematic of an amplifier. There is no input. Call it what you like, but it isn't an amplifier.
Add the input, and then we know where the AC originated...
Clearly AC. (And if you don't treat it as AC, your circuit analysis will be flawed.)
Because you feed an AC signal to the capacitor, and hence you see an AC signal on the other side.
What's your point? Capacitors pass AC and block DC. All you've done is *prove* that there was AC coming out of the AMP (as well as DC).
And clearly you have an alternating voltage on both sides of the capacitor, and an AC current passing through it. Not generated by it, but passing through it.
It is defined by a differential (which necessarily will have a sign reversal), not "polarity" reversals.
*Any* rate of change (differential) that you can detect, means you have detected AC.There simply is no way to do circuit analysis with any other definition.
Or do we really want three states:
A) DC
B) Varying DC[1]
C) AC[2]
[1] Varying DC is exactly like AC and all functions are identical. [2] AC is exactly like Varying DC and all functions are identical.That is 3 states in your mind, and only 2 in fact.
Not very reasonable from a logical point of view, but that is exactly what we do have because of the historical baggage that we carry along.
Remember when every electrical engineer would tell you that current flows from the positive terminal of a battery to the negative terminal... and every electronics engineer would tell you that when the B battery is connected to a vacuum tube circuit the current flows from the cathode to the anode. Of course the positive battery terminal is connected to the anode, so they can't both be correct.
Of course, then solid state electronics came along, and it became clear that current wasn't even necessarily the movement of electrons, but could also be the movement of a lack of electrons! How does
*that* fit your "polarity" requirements?You are telling me the positive terminal supplies the current, and the return path is to the negative terminal. I'm telling you that electrons flow from the cathode to the anode, and I don't care how many reference books you cite saying that current comes from the positive terminal on that battery.
Same sort of historical baggage.
(And can the spelling flames. If you haven't got any better manners than you do logic, you have no place complaining that I forgot to run the spell check on that article. Your claim that the referenced statement was not the non-sequitur that I pointed out it was didn't hold water according to the very definition
*you* supplied!)-- Floyd L. Davidson Ukpeagvik (Barrow, Alaska) floyd@barrow.com
That fits my definition, but not yours! Are you changing your definition or is that just a momentary bit of logical thought?
The states do *not* have to be plus and minus polarity. Just different current levels...
Sure. But it doesn't need to change polarity. All it needs to do is change level.
-- Floyd L. Davidson Ukpeagvik (Barrow, Alaska) floyd@barrow.com
Exactly.
What value does that have? The problem is circuit analysis, which requires the division between DC and AC, and the only division that makes sense is between non-changing current and changing current.
The problem is defining something with no practical value. If AC is a changing current, that includes changing polarity, and covers the actual significant difference from DC. If AC is defined only as changing polarity, we also have to have an entire separate set of identical functions and definitions, one for "varying DC" and one for "AC". Since the analysis is the same, there is no point in separation of the two.
And "varying DC" is a contradiction in terms to begin with. Do we actually need *four* states:
1 -- DC 2 -- Varying DC 3 -- AC 4 -- Steady ACBoy, that should may first year text books *really* interesting!
Either that or we are back to Don Lancaster's correct statement that they are meaningless terms anyway. They certainly are if that is the way they are defined!
-- Floyd L. Davidson Ukpeagvik (Barrow, Alaska) floyd@barrow.com
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.