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... :-)
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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.
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Floyd L. Davidson
Ukpeagvik (Barrow, Alaska) floyd@barrow.com
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.
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Floyd L. Davidson
Ukpeagvik (Barrow, Alaska) floyd@barrow.com
With high frequency and amplitude, a sine wave could be very steep at 0 and 180 degrees. It could also turn sharply at 90 and 270, like the corner of a square wave. You would need low frequency and amplitude for a sine wave to approximate the flat peaks of a square wave.
That part is simple enough for me, but I don't understand harmonics. If you overdrive an amplifier with a sine wave, the output will resemble a square wave. I know the output can be broken down into the input frequency and its odd multiples. I'll have to accept it on faith.
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.
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!)
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Floyd L. Davidson
Ukpeagvik (Barrow, Alaska) floyd@barrow.com
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 AC
Boy, 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!
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Floyd L. Davidson
Ukpeagvik (Barrow, Alaska) floyd@barrow.com
You might want to look into the basis of Fourier analysis. It all falls out of a very simple mathematical property of the sine wave.
If you take any periodic waveform, and multiply its value at every point in time with the value of any frequency of sine wave at the same points in time, over all time and add up (integrate) all the products and divide by the total time (an infinite amount of time), only sine waves that fit an integral number of cycles within the period of the waveform will produce nonzero results (infinite integral divided by infinite time). In fact, it can be shown that you get the same quotient for harmonics if you use any integral number of periods of the waveform, including one period. Testing an infinite number of waves is only necessary to show that non harmonics always produce a zero contribution. For instance, if you test a sine wave that fits
1.000001 cycles into a cycle of the waveform, you don't reach the first zero result till you include a million periods of the waveform (and you get more zeros at every integer multiple of a million cycles, with a smaller and smaller cycle of results between those millions as the number of cycles increases because you are dividing by larger and larger times).
Harmonics (sine waves that fit an integral number of cycles within the waveform) will produce a finite result representing that frequencies contribution to the waveform. (Actually you have to test both the sine and cosine against the waveform to cover all possible phase shifted versions of the sine. Any phase shifted sine can be broken sown into sine and cosine components. Another nice property of sine waves.) Since only harmonics contribute to the total wave shape, you can skip all the other frequencies, and just evaluate the part each harmonic contributes to making the total waveform.
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Well, Floyd, Take a look at the schematics below and you may notice
that while the first one (the one without the cap in series with the
load) puts out a sinusoidally varying unipolar signal, (DC) the second
one (the one _with_ the cap in series with the load) puts out a
sinusoidally varying bipolar signal. (AC)
Now, since the only difference between them is the cap and one puts
out a varying DC signal while the other one puts out a true signal,
then the cap _must_ be generating the AC signal. If you have a
problem with 'generating' then perhaps 'converting' would be more to
your liking. I doubt it though, you seem to be in this only for the
argument and I'm sure you'll come up with reason why you're unhappy
with 'convert'.
No, rather the problem is that many of the fundamental physical sciences and most of electrical engineering use the concept, and it is not used merely by a small corner of circuit analysis. The definition has to work for all the sciences where it may be used. E.g., many switches use the "AC as reversing" concept for quenching contact arcs during switching (as the current passes thru zero as direction reverses) and the defintion of AC as varying DC falls flat for that purpose. Install an AC designed switch on a varying DC circuit, and you may well have a safety switch contacts welded shut. Here, AC DEFINITELY means reversing direction.
I believe the equations are not DC-AC specific - the "AC" term drops to zero if the change in magnitude drops to zero. Your rationale of using the equations does not hold up.
changing in direction or magnitude?
You suggest we use AC is defined as: "regularly or irregularly varying uni- or bi- directional current if it varies at a frequency that could have an effect for that application; unless it is digital, where then the one-time rise time and the fall time of each state change is calculated as AC, too, even though it 'alternates' once for each pulse"
vs.
AC is defined as:
charge flow that changes direction.
which leaves the calculations for reactance out of the definition.
attached
We define air, and black holes, and impracticality. The circular logic that has your AC/DC missing half the paramters of the phenomena also has no use for defining air since we only feel wind, for not defining black holes which have no practical value since we have never seen one, and no use for the definition of impracticality because by definition it has no practical value.
If
not if we consider the two paramters that make up the phenomena - direction and magnitude. And if memory serves me correctly, the "AC" equations are rigorous, and apply equally well to your one-voltage DC when the frequerncy drops to zero- the reactance term of the changing magnitude goes to zero.
Since the analysis is the
no, just two - reversing flow direction, and varying magnitude.
Because the reactance equations only apply to varying magnitude, and they do not apply to reversing direction.
If one has never heard of the ocean, one finds the ocean meaningless. And for the memebrs of that society, they also would find ocean-going boats useless. because they have to define the ocean thru their own experience. As I understood, scienctific method is designed to remove personal views from science. Thus the definition,must stand alone, and since we can't see all that is ahead, science has to fall in behind a definition of that phenomena in pure terms.
imho.......
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Alternating-direction Current, aka Alternating Current
Reality check! Capacitors are passive devices. They do *NOT* generate signals.
All that has happened is the capacitor does not pass DC. You haven't generated AC on one side, you've merely removed the DC.
I don't see how that could be any more obvious. You did take a high school physics class, didn't you? *Use* what you learned!
Okay, so you not only need to restudy high school physics, but differential equations too.
If you had read the definition you posted, you might have noticed that it perfectly described the remark that I was commenting on. It had nothing to do with the discussion.
You are the one stooping to spelling flames.
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Floyd L. Davidson
Ukpeagvik (Barrow, Alaska) floyd@barrow.com
Nothing I said was a flame. And I'd suggest you go practice (a *lot*) before you try me on for a flame war. Especially if you think *that* is a flame.
Apparently I read a lot better than you write.
You write a lot of things that are not valid.
Do you understand that is not significant? The reactance of circuit components, the fundamental significance of AC circuit analysis, does not depend upon polarity alternation in any way. What else is there to talk about? How many chocolate drops should be in each chocolate chip cookie? I await your essay on *something* of significance.
But please, that is the *end* of discussion on your confusion about AC.
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Floyd L. Davidson
Ukpeagvik (Barrow, Alaska) floyd@barrow.com
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