How does network interface card work physically?
This may be more a question of physics, so pardon me if there's any inconvenience.
When I study computer networks, I often read something like this
in order to represent a signal, we place some voltage on one end of the wire and the other end will detect the voltage and thus the signal.
So I am wondering how a signal exactly passes through wire?
Here's my current understanding based on my formal knowledge about electronics:
First we need a close circuit to constrain/hold the electronic field. When we place a voltage at somewhere A of the circuit, electronic field will start to build up within the circuit medium, this process should be as fast as light speed. And as the electronic field is being built up, the electrons within the circuit medium are moved, and thus electronic current occurs, and once the electronic current is strong enough to be detected at somewhere else B on the complete circuit, then B knows about what has happend at A and thus communication between A and B is achieved.
The above is only talking about the process of sending a single voltage through wire. If there's a bitstream and we need to send a series of voltages, I am not sure which of the following is true:
The 2nd voltage should only be sent from A after the 1st voltage has been detected at B, the time interval is time needed to stimulate the electronic field in the medium and form a detectable electronic current at B.
Several different voltages could be sent on wire one by one, different electronic current values will exists along the wire simutaneously and arrive at B successively.
I hope I made myself clear and someone else has ever pondered this question.
(I tag this question with network cause I don't know if there's a better option.)