To summarise, then,Cells and batteries of cells are voltage sources produce fixed voltages. They maintain a constant potential difference chemically (at least until they are depleted of energy, or over-charged to destruction). Their chemical and current sources providephysical construction are such that charges at one end tend to have a fixed currents, but don't otherwise provide any levelamount of controlpotential energy with respect to charges at the other thanterminal. How that happens is for the chemists to know.
The relationship between voltageOther ways exist to produce a fixed potential difference, such as charge pumps, and current is embodied by Ohm's law for resistorsit's sufficient to design a circuit that constantly monitors some potential difference, and if it changes, take some action to restore it. "Pump faster or pump slower", in the same way you occasionally pump air into a varianttyre that has a slow leak, to maintain constant pressure.
At the moment I can't think of Ohm's law which deals with changesany current sources that are able to self-regulate like chemical cells, although probably some such thing exists. However, it's possible to build regulators that maintain a constant current flowing through them, in the same way that voltage regulators do; monitor and current for everything elseadjust. (There are also formulae which deal with
At the relationship betweenrisk of confusing voltage andsources with current for inductors and capacitorssources, which introducein practice it's probably easiest to think of a current source as something that varies its own potential difference to whatever value is required to obtain the variable timerequisite current through whatever's connected to it (and, but that's another topic altogetherconsequently, itself). With resistorsThe result is the behaviour you would expect from a current source; current through it remains fixed while the voltage across may vary. As long as there's no functional difference, this relationshipthere is called "resistance"no distinction between a current source and a voltage source that varies voltage to maintain constant current.
It is not appropriateBy that same argument, you might consider a constant voltage source to apply Ohm's lawbe something that varies current, andto whatever amount produces exactly the concept of ohmic resistancecorrect fixed potential difference across it. Again, a variable current source that maintains a constant potential difference is functionally identical to a fixed voltage source. Both practically and mathematically there's no distinction.
However you envisage these sources, or tothey each only represent a currentsingle quantity in the simultaneous equations that you derive for any system. When you see a voltage source in a schematic, becauseall you know about it, until you solve for all the relationship betweenother variables, is the voltage andacross it. For a current for themsource in a schematic, all you know (until the system is not directly proportionalsolved) is the current through it. How they work is actually irrelevant in the analysis.
You can, howeverCells aside, attribute to them the properties of dynamic resistancebuild practical, whenactive voltage and current sources is not trivial. When you consider their response to changessee a source in eithera schematic, it represents an abstraction of something that, in practice, may have substantial complexity, consisting of transistors and/or op-amps, and other elements, whose role is to make continuous adjustments to maintain some fixed voltage or current.
In that case an idealthe analysis, though, their behaviour is truly trivial. When you see a voltage source can be considered to have zero resistancein a schematic, and an idealyou know the potential difference between two points. That's all. When you see a current source, you know the current in that path. That is considered to have infinite resistanceall.
