Another basic Q - trace charge or current in a circuit?

The battery is like n electron pump that sucks them in at one end and pushes them out the other. The wire and components are made of electrons. When current flows in the loop, all the mobile electrons (which are vibrating all around in every direction) drift around the loop in unison, at least as long as things change slowly enough that you don't have to worry about the speed of light letting some part of the loop get ahead of other parts.

Current is the net movement of charge past some arbitrary reference point in the loop. individual charged particles, like electrons or protons are attracted by oppositely charged particles and repelled from similarly charged particles. Normal matter (with no surface charge (static) or current passing through it, contains a balance of positive and negatively charged particles, over distances larger than molecules. Non uniform balance over distances smaller than molecules is what holds molecules together by electrostatic attraction.

John Popelish wrote in news:A8udnTL5JqfQFDHVnZ2dnUVZ_t snipped-for-privacy@comcast.com:

So the trick with the battery is to set it up in a way similar to how Diodes are described - one end has an electron surplus, the other has an electron deficit, and (if I understand this correctly) the way the Universe works, is that electrons have a much greater tendency to move towards an electron deficit, than to move away from a material to create such a deficit.

Ok, that makes sense to me, because I understood molecular polarity in Chemistry. I guess I got confused by the terminology; I kept thinking of current in the sense of the common useage of water current or air current, which the average person experiences or interprets as a pressure against oneself (or some object) - but, with electronic current, it seems like it's the direction in which the attraction propagates, so to speak (i.e. the lack of electrons that pulls, towards itself, the surfeit of electrons from the negative end).

Thank you for the explanation! - I've printed it out and put it into my notebook.

- Kris

I think that most people now (certainly scientists and engineers) think in terms of "conventional current" - the flow of mythical positive charges form the positive terminal of the voltage source, through the external circuit, and returning to the negative terminal of the voltage source, although we know that, in most circuits, current is actually a flow of negatively charged electrons.

Long ago, when electricity was invented, subatomic particles such as electrons were unknown, so the early scientists arbitrarily declared that current was a flow of positive charge, and based all their calculations on that belief.

During the vacuum tube era, technicians (who were thought not to be as smart as scientists and engineers) were taught using negative (electron) current, as it is difficult to explain the operation of vacuum tubes (particularly cathode ray tubes!) using conventional current.

It doesn't really matter whether you use conventional (positive) current or electron (negative) current when analyzing a circuit, as long as you don't change concepts in midstream. It is probably best to use conventional (positive) current, as that is what most textbooks will use these days.

Peter Bennett wrote in news: snipped-for-privacy@news.supernews.com:

What happened is that, more I thought about it, the more I got confused by more common experiences of current (wind and water), which is the pressure created by the flow of a substance (wind, water, oil) past a sensor (or person ;) ), becasue the flow of electrons moves from the negative terminal, whereas thre is no such thing as a flow of "positve particles" - which then confused me more because that made it seem like resistors, etc., were "in behind" the components they're supposed to regulate.

So the only thing that makes sense to me is the idea, explained by a few kind folks in addition to yourself, of "attractive force". That makes sense to me in terms of, say, the resistor in my simple example controlling, *not* the electron flow, but rather, the strength of the attractive force from the + terminal.

I know it's a picayune/"split hair" detail ;) , but I sometimes can't accept/"get"/comprehend "the usual explanations" that most people just accept, because "the usual" just doesn't make sense to me. So, I got totally confused by people simply saying "well that's how the current flows", becasue I could never understand how something can flow when it ("positive particles") doesn't exist, and "positve stuff" doesn't exist because positrons are locked into atomic nuclei, and therefore can't "flow" anywhere unless the atoms themselves are smashed apart in an acceletrator. So the common everyday simplistic explanation got me completely confused. In university, when the instructor just gave a heavy annoyed sigh and said "Just accept it!", all that happened was that (typical of my response to simplistic non-explanations), I rejected the subject and lost any and all interest in the subject - until recently that is ;) !

So, teh idea of attractive force, as opposed to flwo of some non-existent "positive stuff", and threfore the idea of regulating attractive force, I can understand. In a way, it's like air, if you have two connected chambers, with one bign at sea-level pressure and the otehr being at vacuum

- if there is a valve between the two, the flow of air will be "attracted" by the vacuum because there is a density gradient of air molecules, and, since teh one chamber is at normal pressure/temperature, it obviously is not "pushing", whcih means that the vacuum is "pulling" - and the air flwo will be regulated not only by the valve, but also, by the degree of vacuum, because a strong vacuum relative to the normal chamber means there is a higher/stronger difference in densities, i.e. a higher density gradient.

Anyhoo, that concept helps me understand that the resistor is placed where it is becasue it controls, not the electrons, and not some supposed "flow" of something ("positive thingies") that doesn't exist, but rather, it the amount of attractive forceor (created by a density gradient of charge i.e., electron density) that one is allowing to be exerted by the low-density area upon the high-density area.

Dunno whether that makes sense to anyone else, but it's the only way I finally "got" what teh resistor is actually doing...

At any rate, I definitely appreciate everyone's input on this :) !

Good point, thanks!

- Kris

But flow of water or air is not normally thought of as pressure (at least, not in science and engineering) but as mass or volume per unit if time passing a given observation point. Think of gallons per minute going over a dam. Amperes of current are coulombs per second of charge passing through a point in a circuit. That charge can be pushed by repulsion from one direction and pulled by attraction from the other direction. The effects Are additive and interchangeable. All the stuff of the circuit is full of charges that move essentially as a nearly incompressible fluid, in most situations. Static charge is an exception, where the surface charge acts like a compressible fluid.

A better way to think of voltage as pressure is to imagine a balance of forces on the movable charges in conductors. When you apply voltage across a conductor, you upset the balance of forces and the charges move in reaction to that imbalance.

In the air pressure analogy, there is no suck. Vacuum does not pull on air molecules at a distance, like gravity does. It just pushes on them less than the higher pressure at the other end of the system. The pressure forces are unbalanced on opposite sides of any particular air molecule, regardless of whether any forces are negative or if all are positive but different in magnitude. The effect is the same.

There is a basic law of circuits (Kirchoff's law) that sys that the total voltage drop around any loop has to be zero. The battery pumps up the voltage difference across its terminals, and the rest of the circuit has to develop reverse voltage that uses that pressure up. Flow through a resistor requires (produces) voltage drop. The resistor in that LED circuit uses up all the extra voltage the LED did not need (drop), while doing so at some particular desired current magnitude. In effect, its resistance sets the magnitude of the current by having waste a particular amount of voltage and having a particular resistance. If the resistor did not fol.ow ohms law (was not a linear resistance) its voltage drop would not be proportional to its current, so it would be harder (more complicated math than simple proportionality) to predict its effect in the circuit.

An LED is an example of a device that is not ohmic (not a linear resistance), since its voltage drop is not proportional to its current, but close to proportional to the logarithm of its current.

It's not so much mythical. For example it's very possible to have positive ions in a gas or liquid and they are certainly mobile and actually physically move. In a solid though it's very correct that positive charges or charge carriers basically don't physically move. In those cases the books typically refer to "effective" charge flow. The idea is that when an electron leaves an atom it leaves behind a "hole" and since the atom now lacks an electron is has a net positive charge so the hole is considered to represent a positive charge carrier. When another atom loses an electron it may come fill the original hole and you can consider the effect as if the electron physicall moved from one atom to the next and the "hole" acts as if it moves in the opposite direction at the same time. So some consider that the hole has caried a positive charge from one atom to another.

The concept isn't really hard but it seems like a very convoluted way to think about things. Thats a very real observation. I think I should also say that what I just wrote was for the benifit of the op.

Actually when you consider things from an energy standpoint the conventional current starts to shine. When you consider that the positive charge ends represents a higher potential energy than the negative end, the conventional current has charges moving from a higher energy to a lower energy which is more satisfying than imagining a charge climbing up hill for no reason.

I can still remember my first brush with semiconductors and conventional current and thinking what moron came up with that? The idea spawned a very interesting response or spoof. Try googling for phrase "Bell Labs" dark sucker. Turns out some clever person cam up with the theory that light bulds didn't actually emit light or photons. Instead they actually suck the dark out of the air. Conventional current seems like Alice in Wonderland logic to nearly everyone who is exposed to it but you eventually get over it.

You could think of it as an excess of electrons or negative charges collected together at the negative terminal, and a scarcity of electrons at the positive terminal. The electrons aren't very social and they don't want to stay together, what with like charges and all. When you give them an opportunity or path to get from the negative terminal to the positive they really, really want to spread out and so they will travel from the negative to the positive. The trick is that in order to move towards the positive terminal they have to move a hole or positive as they progress. So the electrons move along the path from negative and they will "effectively" move the holes from the positive to the negative.

Now quite correct. Positive ions are positively charged and are very common. Actually the positive particles in the nucleus are protons and not positrons and you don't need a freestanding protron to have a moveable positive charge. Say you have an atom with two protrons and two electrons. It will have a net neutral charge. Let that same atom loose an electron and you have a moveable electron or negative charge and the remaining atome has two positive charges and one negative charge so it's not balanced and has a net positive charge. In a solid the atom is fixed in place and can't move even when it loses an electron so your thinking is correct in solids. But consider a rain cloud for example. The are many moveable atoms and molecules in a cloud and they easily lose electrons creating moveable positive charges. Sometimes you can see the consequences of this net charge as lightning.

In a liquid based battery like the one in your car a chemical reaction causes molecules to lose electrons to seperate from molecules and the positive charges move through the liquid while the electrons move in the other direction.

Actually if you look at it from an energy standpoint on the crowded side the molecules have higher energy and the vacuum side has lower energy. When you open the valve they will flow from higher energy to lower energy untill the energy differential doesn't exist. So basically the energy is pushing them into the vacuum. It's kinda like falling downhill form higher energy to lower energy rather than being pulled down hill by the lack of altitude.

Actually the location of the resister doesn't matter. As long as the resister is in the path of the current it has the same effect. The idea is that resisters convert energy into heat so any charge traveling through a resister will lose some of its energy to heat. In fact it will lose exactly the same amount of energy no matter where it gets placed.

If that idea doesn't work then try this. Consider the path from the negative terminal to the positive terminal. Lets say the wire, the resister, and the led all look like uphill climbs to the electron. If the climb is high then not many electrons will make the journey and if you lower the climb then many will make it. Now also consider that each electron has some energy currency as it sets out on the climb. Lets say the resister each require a toll in eneergy to be paid. The resister uses the eneergy it gets to make heat while the led uses the toll to make light. The lower the hill the more electrons make the journey and the more tolls paid so the more heat and light you get. When you make the climb higher you get less electrons making the journey and paying tolls so you get less heat and light.

It's the total climb that determines how many make it and how many tolls will be collected and it really doesnt matter if you climb the resister or the led first. In this climb it's strictly single file so theres no way to go part way up the climb and stop. Every electron that starts the journey will finish the journey.

John Popelish wrote in news:oeudnQyveu--KzDVnZ2dnUVZ snipped-for-privacy@comcast.com:

I'm top-posting just to say Thanks, John, for the clarifications :)

This is all helping a lot, and I appreciate that you took the time to explain the concepts - the formulas are having a lot more meaning now, and the circuits I've been looking at are making more sense.

Thanks again :)

- Kris

My pleasure. This sort of thing is what this group for.

in P-type semiconductos there's a quantum entitiy called a 'hole'. and they carry positive charge. the easiest way to demonstrate this (and prove it's not electrons carrying the charge) is to construct a and test hall-efect cell made from p-type semiconductor.

inside semiconductors holes are as real as electrons.

Bye. Jasen

stan wrote in news: snipped-for-privacy@invalid.net:

I'm topposting becasue I don;t have a reply per se, but wanted to asy Thanks! for the additional information - I'm saving all of these great answers and explanations :)

If I seem "overly enthused" sometimes, well, I guess I am, but it's only because I like to express appreciation to people when they're helpful ((and there are certainly quite a lot of people who jump at the chance to express crankiness, hostility, demanding judgementalism, and/or other negative things - and hey, I enjoy bucking that trend ))

- Kris

I'm aware. I was trying to move the newbies understanding along incrementally. I think we both agree the water pressure model will only get you so far and you encounter problems. The old effective hole flow model will get you along pretty far before you need quantum concepts and is arguably simpler. I could be wrong but I think the OP was basically a learning on his own and not and engineering or physics student. When presented a question about current through a resister and an led it seems inappropriate to start with an Einstein-Bose layer discussion. Do you disagree?

stan wrote in news: snipped-for-privacy@invalid.net:

As the OP, I can say, yup, you're exactly right. I did take 2 semesters of physics in University, but that was back in 1978, plus we just skimmed over the most basic concepts of electronics - and even at that, little was realy explained; it was a matter of "here are a few formulas, figure out these problems, can't do it?, too bad, time to move on to the next chapter".

I started off wanting to make some decently-bright solar light units (with four to maybe six white LEDs) that I could put into my stained-glass pieces

- but I then started looking at more complex ideas (battery charging IC and so on), and then, got curious as to what is actually going on in circuitry, well, at least relatively simple circuitry.

There is no EE or even electronics hobbyist to whom I'll ever pose a job threat , but seriously, I just got tired of teh typical consumer bschtick wherein all electronic/electrical devices are pretty much seen as "magical black boxes". That just doesn't satisfy me any more ;)

It's all grist for the proverbial mill, but, like a water-powered mill, sometimes my brain grinds a bit slowly , which is what happend with the question about current - which I do understand better now, thanks to people generously taking time to offer explanations. In my book, any answer that doesn't say I'm just stupid, and instead makes teh effort of trying to explain concepts, is appreciated

- Kris

Sounds like your professor at least sopke english. At one point I thouht I might just have to move to asia and drift around to pick up some languages before I could get through school. I'm not poking fun at people with accents here, I admire people who speak multiple languages. In this case there were two people from his native India and they reported hes was very hard to understand in his native tounge and in class he was somewhere in between and wasn't really speaking either language. He was incredibly smart and a really good guy. To top it off his handwriting was unintelligable to even his teaching assistant. It was quite a semester :)

He did bring up a good point that hasn't been mentioned yet. If you're going to try and get your head around this stuff I would stick to the simpler passive stuff like resisters, capacitors, and inductors till I wasn't feeling lost, then tackle semiconductors. Before anyone jumps on me I'm not saying that electromagnetic fields are simple, I'm saying you can develop a comfortable grip on capacitors and inductors and do quite a bit of circuit analysis without really needing to solve a wave equation or even knowing who Maxwell was. I'm also saying that figuring out a pn junction can be a bit more challenging than a battery and a resistor.