Well, due to popular demand, i will explain conventional current flow.

In short, conventional current flow is a farse, created by man. I offer no direct reason for why it came to be, but i can explain the action that takes place.

If a conductive material has no potential difference across it there will be no net imbalance of electrons within the conductor. This is shown in the "open switch" scenario in the animation below. I have it shown as electrons (.) dots, not moving or doing anything in this frame. Trueth be told they are moving about, but in no real direction, simply vibrating according to the temperature that surrounds them.

When the switch is closed, a potential difference appears across the circuit, and the first thing that happens is coulombs of electrons are ripped away creating an elctrostatic "vacuum". (This is what i refered to energized Coulombs wanting to get to their happy place, ie. sitting around and vibrating).

The "electrostatic" vacuum forces the electron beside it to get suck into its place. This causes a similar effect to the next electron, etc, etc, etc. This goes all the way around the loop until the the battery looses its electron it ripped away. And the process repeats itself.

So now your wondering why all my analogies indicate current as flowing in exact oposite of what im now showing you. Well the reason is my analogies were made in the regard of Conventional Current Flow. This is the standard that all electrical people work with. (Only physics people, those die hard keeners, insist on regarding the current flow of electrons for what it realy is).

Conventional current flow is simply the flow of "holes" (electrostatic vacuum points), since "holes" yank the electrons into it in a clear direction. Likewise all that yanking DOES move electrons in the oposite direction, however this is coined "Unconventional Current Flow" for unconventional people (physics majors ;) ).

Below should now see holes moving around the loop clock wise (Conventional Current Flow), while electrons are moving counter clockwise (Unconventional Current Flow).

I would also like to add a note at this point and stress that this is not an issue to get all strung out on. Its good to know, but for "practical" electronics, you do not need to continously remind yourslef of this true nature. Keep your head orientated with the Conventional Current flow direction ;)
Posted on 2003-04-10 19:37:05 by NaN
Likewise, i should also be more honest explaining insulators. But first, a bit more on conductors.

Conductors have an abbundance of electrons (approximately one "easy to get at" electron per atom). They are not extra atoms, just the easiest electron to get your hands on. Its these electrons that are being yanked around under the "electrostatic vacuum", which develop our Conventional Current Flow.

Insulators however, have their electrons barred up and caged. They are not easy at all to "yank" away from their atoms. If no electron is yanked under the electrostatic vacuum induced by the batteries Voltage, then there will be no unconventional or conventional current flow. This is why we say the entire voltage drops across the insulator. There is high vacuum on one side, and no vacuum at all on the other side. Hence, no electrons are moving through the insulator, because the "vacuum" is not strong enought to breakdown their "cage".

Now i realize this sounds a bit odd, because ground is suppose to have the same principal. Well it does, except that ground is in a conductor were electrons can "party" and move freely. In no clear order, an overlooked partier can be kidnapped and pulled into the circuit. This upsets the partying electrons at ground, and demands that the battery give then another electron to party with.

So in this sense ground has no net "Vacuum" of Voltage. They get replacement partiers as need from the battery, so they dont even try to get YOUR electrons when you touch ground, with say your finger. However anywhere else, where there may be a Voltage (or "vacuum"), electrons will be snatched up in any way possible. This is why we insulate wires... to keep us safe.

More on Grounding:

Ground is defined by the negative terminal on a battery, or the 0V point. Either or!. Remember voltage is a potential difference. So in theory for 0V, we could say the positive end wire is ground, after all, the potential across both ends of the wire attached to the positive 12V is: 12-12 = 0V! (Remember, Voltages In parallel are equal, so there difference is 0!)

Does this seem right? Well it can be, if you design it to be. The result would be a NEGATIVE VOLTAGE. After all we are defining ground at the positive terminal by 12V- 12V=0, and so like wise the negative terminal 0V - 12 V = -12V.

This is a weird kind of limbo, if its the first time you've been expose to such trickery ;) . To help keep things "down to earth" (yes, i had to say that :grin: ), its common practice to note where in a ciruit the considered EARTH GROUND will be.

The Earth Ground is a Symbol drawn as:


The earth, being massive, and the biggest party an electron could hang out in is the best referece available for a purely 0V potential. So by assigning a node as earth ground, its without question the 0V starting point for circuit design and analysis.

What about batteries, and flashlights. Well they have what we refer to as floating grounds. Like countries with local governments. Not all contries have to agree on their polocies, however they all have similar infastructures. They all have their own "take" on what ground is. (Common practice is to assume the NEGATIVE terminal of the batteries). However, there is no promise that the negative from two separate flashlights are exactly at the same would be "zero" value that their circuits operate under. There could very well exist a potential difference between each Negative from each flashlight!

For people making USB devices and other computer components, they need to be sure that the ground on their device matches ground on the computer. With out this assurance, electrical damage could occur. So this is a potentially destructive problem! The solution is to offer ground as best and as easily as possible. The Computer cabinet, as well as port pins, are all tied to ground. The idea is to maximize the likelyhood that "common negatives" ( ie Ground ) on both devices are contacted before any other pins with Voltage on them. This ensures that the CPU sees 5Vs when a USB hub offers 5V. If the ground is not made first, the hub thinks its offering 5V's (as referenced by its internal battery) but the CPU might see 15 volts (as referenced from the CPU ground only). This scenario is because the grounds are not made common between each device first, and there exists a potential difference between them.

Look at your USB connectors. You'll see they desparitely try to ensure ground is always the first connection made with any other electronic device. And now you know why! Random voltages are not nice on silicon chips not expecting it ;)
Posted on 2003-04-10 20:31:30 by NaN
More on the topic of floating grounds. If any of you have seen the movie "The Hunt For Red October", there is a good example of this principal at play in it.

When they are trying to board the Red October in the middle of the Ocean, a hellicopter is hovering above trying to lower the hero onto the sub. The hellicopter and all its electronics are woking fine (local to the hellicopter), however, the rotor blades, wizzing through the dense moist air, and ripping easy to get at electrons from the water molecules in the air, and building an overal static voltage all over the hellicopter. Since the hellicopter's local ground would be its body and chassy, all electrical circuit and computer voltages would be 5 Volts higher than ground. Hence all circuits continue to work as they were designed to.

However, since the sea is wrapped around the earth itself, it is the TRUE judge of what ground is! From the sea's point of view, it sees a hellicopter charged to 200,000V all over its body and local ground! Likewise, the hellicopters electronics would then be seen to be operating at 200,005 Volts!

This is why in the movie, they are trying to attach a GROUND ROD from the hellicopter to the submarine first! Doing so would safely discharge the hellicopters gained excess of electrons (and hence local ground voltage). Once done, grounds are made common between both vehicals, and there is no risk of discharge happening through the human instead!

But the movies, are dramatic, and instead some "star-trek ensan" gets zapped as he brushes agains the ground rod before connection is made, and is knocked out! Simply because the ground was not connected first, and the eager electrons chose to use the human as the last leg of their journey.

If you eventually design things for your computer. Remember this tale and be mindfull to ensure your computer sees the same ground your electronics does! You dont want to be knocking out any computer ports, or worse, your processor!
Posted on 2003-04-10 20:46:26 by NaN
To further this conversation a touch further. A person can be viewed as the "other device" interfacing to a computer.

Around here it gets very cold in the winter. I tend to wear my fuzzy slippers when im at home to keep my feet warm. But they statically rip electrons from my carpet with every step i take! So after a trip to the kitchen and back myself may have 10, 000 volts all over my body. All computers are safely grounded to earth ground, so as i come near, the computer see me as a 10,000 V walking battery! I grab my keyboard and ZaP, i discharge through the keyboard, through the keyboad port, and onto the CPU circuitboard ground. (This is not nice to a computer ~ to it, im a lightning bolt!).

So how i remedy this is i have scrapped a small 1/2 centimeter circle of paint away from my CPU case on the top. Every time i sit down to my CPU in the winter, i quickly reach over and touch the top of my CPU and discharge safely into the CPU's chasis, which shunts directly to earth ground. This is totaly safe and has not effect on the computer. So then i can start typing, and be no risk to my CPU.
Posted on 2003-04-10 21:50:27 by NaN
In short, conventional current flow is a farse, created by man. I offer no direct reason for why it came to be, but i can explain the action that takes place.

The man was Benjamin Franklin. You know, that old fat fool with the kite in the lightning storm?

Actually, he was establishing the electrical nature of lightning, and he developed the first effective protection from strikes. Its still used today.

While he was at it, he was modeling what electricity was. He likened it to a fluid froling from one electrical potential to another; either a positive charge going from + to -, or a negative charge going the other way. As he had no theory or way to determine which was the case.... he guessed.

And he guessed wrong.

Everyone learning electronics ever since has to go thru the time where they learn about the "two currents." The short answer is electron flow is what actually happens, but conventional current is what you pretends happens and talk about.

And no, you don't seem any smarter if you insist it flows the other way, you'll just confuse peoiple until you too pretend it goes backwards.
Posted on 2003-04-12 14:25:37 by Ernie