Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How do the electrons move in a network cable?

  1. Jul 3, 2008 #1
    I spent all day yesterday trying to find the answer to this without success. I know it must be out there, perhaps I just don't know the correct terminology to use in order to find it.

    My question is this:
    When I transfer data from one computer to another, the network card in the first computer does something, which causes the electrons in the cat5 to do something, and the network card in the second computer is able to understand this something as data which is displayed to the user.

    What I want to know is what those somethings are, especially what actually goes on inside the cat5. For example, if I were to graph the current/voltage of the cat5 over time, what would it look like? How would it differ between one piece of data and another? And how does the computer that is receiving the data interpret these currents as being data?

    All I have been able to find are higher level explanations (e.g. "The computer sends a packet..."), nothing that explains what is happening on the physical level. If anybody could help me with this that would be awesome! Thanks!
  2. jcsd
  3. Jul 3, 2008 #2


    User Avatar

    Staff: Mentor

    The key term here is "transmission line". The information travels down the transmission line as an electromagnetic wave:


    Information is typically transmitted with some modulation scheme:


    The information can be baseband (the information is transmitted at about the same frequency as the AC signal in the TL), or it can be mixed up in frequency to modulate an RF carrier wave.

    In any case, the electrons in the two wires of the twisted pair of your Cat-5 cable are just vibrating back and forth a very short distance (less than a mm, I would think, but I'm not going to calculate it right now), at whatever frequency the EM wave is that is propagating down the twisted pair TL. The electrons do not move down the wire carrying information. They vibrate in sync with the propagating EM wave that is transferring the information down the Transmission Line at about 2/3 the speed of light.
    Last edited: Jul 3, 2008
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook