When I press a key on my keyboard, it will alter the flow of electrons in a wire connecting to send data to my computer. Let's say it sends the bits: 100000000100000000100000000100000000, which is a few letters encoded in binary and ASCII.
These electrons somehow move down the wire, to a chip, that detects where my data should go with transistors, or as I understand it, little switches that can be controlled with another wire. The chip will detect where my data is heading, and send it in the right direction.
So the question is, if I make a HTTP request from Europe to a server in USA, do some of electrons from my PC, in 200 ms the response takes, travel across the Atlantic ocean to USA and come back to me?
Best Answer
When you push an electron into one end of a wire, they all jostle around a bit, and a different one pops out the other end.
In a conductor (e.g., any metal) there is a certain fraction of the electrons that are not bound to any particular nucleus and these roam freely throughout the conductor all of the time, even when there's no external voltage applied. Applying a voltage simply causes a net "drift" of this sea of electrons in the direction of the electric field. The speed of this drift is orders of magnitude slower than the speed the electric field propogates (which is basically the speed of light).
The answer to whether any particular electron might make it from one end of the wire to the other depends on the length of the wire and the signaling frequency. The drift speed divided by the signaling frequency would give you the average distance an electron might travel in one cycle. (I hesitate to call this "wavelength", but it's the same concept.) If the wire is shorter than half of this distance, some electrons are making the whole trip.
Signaling frequency is important, because in the example you give, both USB and Ethernet use AC signals at rather high frequencies. The electrons really don't move very far at all.
And to address your other point, about electrons from the input of a module appearing at its output — no, this is rarely true. Capacitors, transformers, tubes, FETs and most bipolar transistor circuit configurations prevent this. There are many places in your transatlantic trip where the direct flow of electrons is deliberately blocked, so no, "your" electrons definitely don't make it across the Atlantic.