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Speed of signal

  1. Apr 9, 2005 #1
    If an AC circuit has a certain frequency of oscillation, let's say undamped, i.e. first order. Then there is a way to figure out the wavelength and therefore speed of the signal? Does that mean that signal does not travel at speed of light all the time, but can potentially?

    Thanks in advance.
  2. jcsd
  3. Apr 9, 2005 #2


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    Staff: Mentor

    The frequency of an AC signal has nothing to do with its propagation speed.
  4. Apr 9, 2005 #3
    then does electric signal travel at speed of light?
  5. Apr 9, 2005 #4
    An electrical signal will travel according to the surrounding media in a typical PC
    card the speed along a track of a pulse will be quite a bit less than light speed -- look
    up 'Transmission Line theory'

    speed = C / sqrt(k) where C = light speed and k is the permitivitty
    of the surrounding dialectric , for buried PC tracks k = 4-5
    Somtimes in chips gold air spaced wires may be used to avoid delays.
    rate of 15 cm per nSEc would give you some idea --- But for sine propagation if the wavelength is longer that this i.e < 1 GHz then the energy transmission rate will be less than the delay because you need to receive
    cyles to be meaningful

    Last edited: Apr 9, 2005
  6. Apr 11, 2005 #5
    If you are doing basic circuit analysis, you can assume your circuits are ideal, and analyze them as though the described situations take effect instantaneously.

    That is you can make this assumption since the signals travel at NEAR the speed of light--- so if the system is physically small the electric signals move through it fast enough so that you can consider them to affect every point in the system simultaneously. You would do well to know that a system that is small enough is called a lumped parameter system.

    In circuit theory, we just assume this is true... however in electromagnetic field theory, we cannot assume this, and you will learn this in your future EE courses in applied EM and antenna theory--- should you choose to go that route in your studies.
  7. Apr 11, 2005 #6
    Ooooh, thanks. I was wondering about lumped circuits...

    Everyone's answer combined gives me a better idea about it!
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