AC Circuits: Signal Speed & Wavelength Calculation

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Discussion Overview

The discussion revolves around the propagation speed and wavelength of signals in AC circuits, particularly in relation to frequency and the media through which the signals travel. It touches on theoretical aspects, practical implications, and circuit analysis methodologies.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the wavelength and speed of a signal in an AC circuit can be determined based on its frequency, suggesting that the signal may not always travel at the speed of light.
  • Another participant asserts that the frequency of an AC signal does not influence its propagation speed.
  • A subsequent post inquires if electrical signals travel at the speed of light.
  • Another participant explains that the speed of an electrical signal is dependent on the surrounding media, referencing Transmission Line theory and providing a formula involving the speed of light and the permittivity of the dielectric.
  • One participant notes that in basic circuit analysis, signals can be assumed to travel instantaneously in ideal circuits, particularly in small systems referred to as lumped parameter systems, while emphasizing that this assumption does not hold in electromagnetic field theory.
  • A later reply expresses gratitude for the insights on lumped circuits, indicating that the combined responses have clarified the participant's understanding.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between frequency and signal speed, with some asserting that speed is independent of frequency while others suggest that it may vary based on the medium. The discussion remains unresolved regarding the exact nature of signal propagation in AC circuits.

Contextual Notes

Limitations include assumptions about ideal circuit behavior, the dependence on specific media properties, and the distinction between lumped and distributed parameter systems, which are not fully explored in the discussion.

Who May Find This Useful

This discussion may be of interest to students and professionals in electrical engineering, physics, and anyone exploring the principles of AC circuits and signal propagation.

EvLer
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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.
 
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The frequency of an AC signal has nothing to do with its propagation speed.
 
Ok,
then does electric signal travel at speed of light?
 
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

Ray.
 
Last edited:
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.
 
Ooooh, thanks. I was wondering about lumped circuits...

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

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