# Please correct my understanding of “how electric works”

Being in Information Tech, I'm good with programming languages, processor logic, and the such. It's only natural I got curious about that outlet I plug my servers into. Here is where I am:

I tried to understand volts and amps. The water analogy seemed okay at first, but I have tons of issues with it. I don't think it's exactly right.

Regardless, this is where I am currently stuck:

Do electrons physically hop from atom to atom in a circuit? Are they really leaving one atom and onto the next, so to speak? Just "slowly" but the pressure of this is what makes my light bulb turn on immediately? Electrons vs. Electric Charge? If so, does a larger charge (voltage?) make the electronics physically move quicker?

I'm trying to understand electricity 101 here and Google presents a LOAD of conflicting data, opinions and arguments.

Please set me on the right track.

• This is more of a physics question than an electronics one. You very rarely need to worry about individual electrons when designing or building a circuit. – David Jun 2 '14 at 21:46
• @David You don't use electron analysis to solve for circuit voltages?! – OJFord Jun 3 '14 at 1:32

Well, electrons hop, but slowly.

Let's get a bit deep in your questions: electricity flows in metals because their atom are bond by the metallic bond. That means that the nuclei are organized in a nice lattice, or at least they are still, while the electrons are free to move. Since we can't really nail down where an electron is we say that the probabilty of an electron being around a nucleus is the same for each nucleus.
When you have a single atom instead its electrons are well organized around it, and only it.

You can try to imagine that as a regular, 3-D grid where each node is a nucleus, and all the electrons are a sort of cloud.

Now, these little guys move very fast. Their speed increases with temperature, but here comes the trick: since they don't prefer a particular direction on average they do not move. And since current is defined as flow of charge per unit of time, well, there still is no current.

Imagine to cut a wire with a surface, and start counting the electrons that are going through it. There would be a lot of them going right to left... And vice versa. So the so called net charge flow is zero.

Now apply an electric field to the wire, i.e. connect it to a battery: the electrons now have a favourite direction, that is the lowest energy direction. Low energy for an electron (negative charge) means high electric potential, so the whole bunch of them starts to move towards the positive pole of your battery. Be careful, this does not mean that they stop moving randomly around, it just means that, on average, they are moving towards plus.

I don't really have an example for that, you know those seeds with a sort of wing on them, on a windy day they can fly for quite a distance: they move randomly but ultimately they follow the wind.

Now you have current: if you imagine to cut your wire again the electrons flow is not balanced any more. The so called drift speed of the electrons is very, very low, some mm per minute. So how is that you don't have to wait hours for your light to turn on? That's because all the electrons of the wire start moving simultaneously. The point is that when you apply an electric potential to a long wire, i.e. you close the switch, the potential is distributed along it. So for each tiny slice of wire you will have a potential difference, thus a drift speed, thus a current. This thing is almost istantaneous, and can be as fast as light (but it's slower).

Hope that's enough for your first question, now the others:

Electrons vs Electric Charge

Well electrons are physical objects, they have a mass, dimensions, and charge. Charge is a physical quantity. That's as you were asking the difference between a mountain and height: a mountain, among other characteristics, has a certain height that can be expressed in meters. An electron, among other characteristics, has a certain charge that can be expressed in coulombs.

Larger charge/voltage $\rightarrow$ faster electrons

First of all charge and voltage are two completaly different things. The higher the voltage, that is the larger the electric potential, the larger the electron speed and then the larger the current. Larger charge means larger current if that charge is moving, if you just use a bigger wire that contains more electrons you will have a larger current only because the resistance of the wire is lower.

Valence electrons in conductors generally form a cloud or swamp within/around the conductor lattice. Each electron has its own potential and therefore wants to stay away from the rest of the electrons (while still attracted to the protons in the lattice of the conductor). These free floating electrons are the water in the hose analogy. When you hook a battery up to the conductor, a "pressure" is exerted on this cloud/swamp of electrons and they start flowing as soon as a switch closes the circuit. Excess electrons from the negative terminal of the battery start moving through the conductor to the positive terminal. Just like a hose full of water though, very shortly after you open the main faucet, you can start washing your car. As long as the hose is full of water, you only have to wait for the pressure wave to travel through the hose (not the water that started at the faucet).

This will allow you to calculate the speed of your electrons. The electrons velocity is directly proportional to the voltage. But the electron velocity isn't generally what one cares about when turning on a lightbulb (it's the pressure wave).

The pressure wave that I spoke of allowing you to get water at the other end of the hose virtually immediately has an inherent speed based upon the material properties of water itself. Similarly, electric waves travel at the speed of light. No increase in voltage will change this.

The reason why some electronics work faster when you apply high voltage is because of inherent capacitance in some circuits. This can be thought of as a hose that has a lot of stretch/flex to it. If you have this hose with a high pressure nozzle on the end, and then have a sensor at the nozzle of the hose waiting for it to reach a certain pressure/speed, you would have to wait for the strechable/flexible hose to expand until it can't stretch any more. At that point, no more water can fit into the expanding hose and so it starts to squirt out of it at high pressure at the nozzle. This is the delay that semiconductor switching has to deal with. It has to wait for the hoses to expand to full size before it will detect the pressure is at a certain value and then take some action based upon that pressure. Note that in this case, the water pressure wave still moved at the same speed, but the pressure at a point (the nozzle) was delayed due to the stretching hose action.

In the case of a lightbulb, since it has very little capacitance, increasing the voltage will not turn it on significantly faster.

In a conductor, the electrons are free to move about. In fact, they are constantly moving about. Just like molecules in a gas or liquid. There movement is partly random, but on average electrons move to even-out voltage levels, just like molecules move to even-out pressure levels.

The average movement of electrons is mainly driven by electro-static forces: charges either attracting or repelling each other. In gasses or liquids, molecules simply bump into each other like with the swinging marbles in Netwon's cradle.

You can compare electrons moving in a conducting wire with the swinging marbles: as soon as the marbles hits at one end, the marble at the other end starts its swing. The propagation of the impact is much faster than the speed with which the marbles themselves move.

In a gas or liquid, changes in pressure are propagated with the speed of sound for that medium. Changes in charge are propagated with the speed of light. Thus electricity will flow (almost) immediately after turning on a switch. Just like water will flow immediately when you open a faucet, regardless of how fast the water flows through the pipe.

Just as with water, the speed with which electrons move is determined by the voltage over the conductor (in water: the pressure difference), and its resistance. One Ampere of current is defined as the movement of one Coulomb or approx. 6.241×10^18 electrons per second through a conductor. Depending on the material, there will be a specific number of free electrons per volume that together supply this movement. From the number of free electrons and the current, the actual average speed of the electrons can be calculated.