Voltage-driven charge-flows

First of all, you must abandon the idea that current travels in transistors or flows inside of wires. Yes, you heard me right. Current does not flow. Electric current never flows, since an electric current is not a stuff. Electric current is a flow of something else. (Ask yourself this: what's the stuff that flows in a river, is it called "current?" Or is it called "water?")

Since a current is a flow of charge, the common expression "flow of current" should be avoided, since literally it means "flow of flow of charge." - MODERN COLLEGE PHYSICS, Richards, Sears, Wehr, Zemanski So what flows inside of wires?

The stuff that moves within wires is not named Electric Current. Intead it is called Electric Charge. It's the charge that flows, never the current. The motion of charges can vanish, and the motion can appear. But the motion itself doesn't flow along, it's the charges which flow. And in rivers (or in plumbing,) it's the water that flows, not the "current." Analogy: we cannot understand plumbing until we stop assuming that the pipes are empty ...while also believing in a magical stuff called "current." We must learn that pipes are already full; that "water" flows inside them. The same is true with circuits. Wires are not filled with "flow of Current," instead they are pre-filled with charge. Charge which can move. Electric charge is real stuff; it's carried by physical particles, and it can move around with a real velocity and a real direction. Charge behaves much like a "stuff," like a gas or a liquid. But electric current is different from charge: charge is like a stuff, but current is not a stuff. (If current is like wind, then charge is like Nitrogen!) If we experiment with concepts; if we decide to ignore "current," and instead we go and carefully examine the behavior of the moving charges in great detail, we can burn off the clouds of fog that block our understanding of electronics.

Second: the charges found within conductors do not push themselves along, but instead they're pushed by "potential difference;" they're pushed by the voltage-fields within the conductive material. Charges are not squirted out of the power supply as if the power supply was some sort of water tank. If you imagine that the charges leave through the negative terminal of the power supply; and if you think that the charges then spread throughout the hollow pipes of the circuit, then you've made a fundamental mistake. If you think that the charges are provided by the power supply, then you've made a fundamental mistake. Wires do not act like "empty electron-pipes." A power supply does not provide any electrons. Power supplies certainly create currents, or they cause currents, but remember, we're removing that word "current." To create a flow of charges, a power supply does not inject any charges into the wires. The power supply is only a pump. A pump can supply a pumping pressure. Pumps never supply the water being pumped.

Third: have you discovered the big 'secret' of visualizing electric circuits? ALL CONDUCTORS ARE ALREADY FULL OF CHARGE Wires and silicon ...both behave like pre-filled water pipes or water tanks. The "water" is the vast population of movable charged particles of the conductor. Electric circuits are based on the "full pipes analogy." This simple idea is usually obscured by the phrases "flow of current," or "power supplies send out current." We end up thinking that wires are like hollow pipes. We end up visualizing a mysterious substance called Current which flows through them. Nope. (Once we get rid of that word "current," we can discover fairly stunning insights into simple circuits, eh?)

If circuits are like plumbing, then none of the "pipes" of a circuit are ever empty. This idea is extremely important, and without it we cannot understand semiconductors ...or even conductors! Metals contain a vast quantity of movable electrons which forms a sort of "electric fluid" within the metal. A simple hunk of copper is like a water tank! Physicists call this fluid by the name "electron sea of metals," or "the ocean of charge." Semiconductors are always full of this movable "charge-stuff." The movable charge is in there even when a transistor is sitting on the shelf and disconnected from everything. When a voltage is applied across a piece of silicon, those charges already within the material are driven into motion. Also note that the charge within wires is ...uncharged. Every movable electron has a positive proton nearby, so even though the metal contains a vast sea of charge, there is no net charge on average. Wires contain "uncharged" charge. Better call it "cancelled charge." Yet even though the electrons are cancelled by the nearby protons, the electrons can still flow among the protons. Cancelled charge can still move around, so it's possible to have flows of charge in an uncharged metal.

OK, since the "pipes" are already full of "liquid," then in order to understand circuitry, we should NOT trace out the path starting at the terminals of the power supply. Instead, we can start with any component on the schematic. If a voltage is applied across that component, then the charges within that component will start to flow. Let's modify the old "flashlight explanation" which we all were taught in grade school. Here's the corrected version:

AN ACCURATE FLASHLIGHT EXPLANATION:

Wires are full of vast amounts of movable electric charge (all conductors are!) If you connect some wires into a solid ring, you form an "electric circuit" which contains a movable conveyor-belt made of charges within the metal circle. Next we cut this ring in a couple of places and we insert a battery and a light bulb into the cuts. The battery acts as a charge pump, while the light bulb offers friction. The battery pushes the wires' long row of charges forward, then all the charges flow, then the bulb lights up. Let's follow them.

The charges start out inside the light bulb filament. (No, not inside the battery. We start at the bulb.) The charges are forced to flow along through the filament. Then they flow out into the first wire and move along to the battery's first terminal. (At the same time more charges enter the filament through its other end.) The battery pumps the charges through itself and back out again. The charges leave the second battery terminal, then they flow through the second wire to the bulb. They wind up back inside the light bulb filament. At the same time, the charges in other parts of the circuit are doing the same thing. It's like a solid belt made out of charges. The battery acts as a drive- wheel which is moving the belt. The wires behave as if they hide a conveyor belt inside. The light bulb acts like "friction;" it gets hot when its own natural charges are forced to flow along. The battery speeds up the entire belt, while the friction of the light bulb slows it down again. And so the belt runs constantly, and the light bulb gets hot.

The truth will set you free ...but first it will piss you off! -anon

Brief review:

1. THE STUFF THAT FLOWS THROUGH CONDUCTORS IS CALLED CHARGE. ("CURRENT" DOESN'T FLOW.)

2. THE CHARGE INSIDE CONDUCTORS IS SWEPT ALONG BY VOLTAGE FIELDS.

3. ALL WIRES ARE "PRE-FILLED" WITH A VAST AMOUNT OF MOVABLE CHARGE

4. BATTERIES AND POWER SUPPLIES ARE CHARGE-PUMPS.

5. LIGHT BULBS AND RESISTORS BOTH ACT "FRICTIONALLY."

One last thing: The difference between a conductor and an insulator is simple: conductors are like pre-filled water pipes, while insulators are like pipes choked with ice. Both contain the "electric stuff;" conductors and insulators both are full of electrically charged particles. But the "stuff" inside an insulator can't move. When we apply a pressure-difference along a water pipe, the water flows. But with an empty pipe, there's nothing there, so the flow does not occur. And with an ice-choked pipe, the stuff is trapped and doesn't budge. (In other words, voltage causes charge-flow in conductors, but it can't cause charge-flow in insulators because the charges are either missing, or immobilized.) Many intro textbooks get their definitions wrong. They define a conductor as something through which charges can flow, and insulators supposedly block charges. Nope. Air and vacuum don't block charges, yet air and vacuum are good insulators! In fact, a conductor is something that contains movable charges, while an insulator is something that lacks them. (If a book gets this foundational idea wrong, then most of its later explanations are like buildings built on a pile of garbage, and they tend to collapse.)

One more last thing before diving into transistors. Silicon is very different than metal. Metals are full of movable charges... but so is doped silicon. How are they different? Sure, there's that matter of the "band gap," and the difference between electrons versus holes, but that's not the important thing. The important difference is quite simple: metals have vast quantities of movable charge, but silicon has far less. For example in copper, every single copper atom donates one movable electron to the "sea of charge." Copper's "electric fluid" is very dense; it's just as dense as the copper metal. But in doped silicon, only one in every billion atoms donates a movable charge. Silicon is like a big empty space with an occasional wandering charge. In silicon, you can sweep all the charges out of the material by using a few volts of potential, while in a metal it would take billions of volts to accomplish the same thing. Or in other words: 6. THE CHARGE INSIDE OF SEMICONDUCTORS IS LIKE A COMPRESSIBLE GAS, WHILE THE CHARGE INSIDE OF METALS IS LIKE A DENSE AND INCOMPRESSIBLE LIQUID. Sweeping away the charges in a material is the same as converting that material from a conductor to an insulator. If silicon is like a rubber hose, then it's a hose which contains compressible gas. We can easily squeeze it shut and stop the flow. But if copper is also like a rubber hose, then instead, it's like a hose full of iron slugs. You can squeeze and squeeze, but you can't smash them out of the way. But with air hoses and with silicon conductors, even a small sideways pressure can pinch the pathway shut and stop the flow.



OK, let's look at the way that transistors are usually explained.

To turn on an NPN transistor, a voltage is applied across the base and emitter terminals. This causes electrons in the Base wire to move away from the transistor itself and flow out towards the power supply. This in turn yanks electrons out of the P-type base region, leaving 'holes' behind, and the 'holes' act like positive charges which are pushed in the opposite direction from the direction of electron current. What SEEMS to happen is that the base wire injects positive charges into the base region. It spews holes. It injects charge.

(Note that I'm describing charge flow here, not positive-charge "conventional current.")

