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Thread: Speed of Electricity

  1. #1 Speed of Electricity 
    AAK
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    Sorry for my lack of knowledge on the subject (I am a junior in high school), but I'd like an answer to a question I've asked myself.

    From what I know:
    Electricity flows at C (speed of light in a vacuum), though the electrons themselves do not
    Though some things better than others, everything conducts electricty


    If hydrogen ions (no electrons) can be bonded to create something like a ionized hydrogen (or anything) "wire" and is used in an alternating current, will the speed of electricity in it be C? What I thought is that since there are no electrons in the wire for a battery to push, will the speed of electricity depend on the electron(s) that travel through the hydrogen and back?

    Maybe this is stupid and I'm missing something, but whatever, I'd like to know.


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  3. #2  
    Forum Isotope Zelos's Avatar
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    if there is no charge that can be moved there cant be any electric current, and it doesnt matter what ure using the speed is allways C


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  4. #3 Re: Speed of Electricity 
    Forum Radioactive Isotope mitchellmckain's Avatar
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    Quote Originally Posted by AAK
    Electricity flows at C (speed of light in a vacuum), though the electrons themselves do not
    Though some things better than others, everything conducts electricty
    Very nice question!!!!

    I have a masters in physics and I had to search a bit before I found and answer that satisfied me. I felt surely that the properties of the materials must play a role.

    Well I learned a great deal while investigating this.

    The electrical signal is due to an electromagnetic wave (light) which would have the speed of light in the materal. If the electromagnetic wave travels in copper this would be 41% of the speed of light in a vacuum because 2.43 is the index of refraction of copper. On the other hand, I figure it is likely that the electromagnetic wave travels outside the metal that conducts the electricity in the air that surrounds it and in air, light travels at nearly the same speed as in a vacuum.

    However, electrical signals are usually transmitted in a pair of wires (in which the current flows in opposite directions) and the velocity of the signal is effected by the mutual inductance of the two wires and thus depends on the capacitance between the two wires. The result is that the velocity of the signal is strongly influenced by the dialectric of the material between the two wires, and is thus the 100% of the speed of light for air insulated wires and 38% of the speed of light for rubber insulated wires.
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    For RF (which are basically modulated electrical signals) through copper wires, say RG6 or even .500, velocity of propagation is about .78C. This, of course, depends on the wavelength. Additionally, twin leads will give you a better VOP than coax.
    However, electrical signals are usually transmitted in a pair of wires (in which the current flows in opposite directions) and the velocity of the signal is effected by the mutual inductance of the two wires and thus depends on the capacitance between the two wires.
    Generally, this phenomenon is reduced to a negligible factor by the use of insulated stranded wires virtually eliminating eddy currents, inductance, and skin effect.
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    Forum Radioactive Isotope mitchellmckain's Avatar
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    Quote Originally Posted by CaveatLector
    For RF (which are basically modulated electrical signals) through copper wires, say RG6 or even .500, velocity of propagation is about .78C. This, of course, depends on the wavelength. Additionally, twin leads will give you a better VOP than coax.
    I would appreciate knowing the source of your information because I have found the variety of sources and opinions on this matter to be quite confusing. It is not that I am doubting you a propagation of .5c or .78c would make sense as the result of combined transmission through both air and conductor.


    Quote Originally Posted by CaveatLector
    However, electrical signals are usually transmitted in a pair of wires (in which the current flows in opposite directions) and the velocity of the signal is effected by the mutual inductance of the two wires and thus depends on the capacitance between the two wires.
    Generally, this phenomenon is reduced to a negligible factor by the use of insulated stranded wires virtually eliminating eddy currents, inductance, and skin effect.
    But the sources I read suggested that the insulation actually slowed down the transmission speed depending on the dialecric properties of the material.
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    I would appreciate knowing the source of your information because I have found the variety of sources and opinions on this matter to be quite confusing. It is not that I am doubting you a propagation of .5c or .78c would make sense as the result of combined transmission through both air and conductor.
    The info comes from several years experience in the telecommunications industry, mainly fiber optics.
    This says that VoP is about .75C for RG-6 coax with foam dielectric, which is very common.
    We use a lot of .500 to .875 inch trunk lines in our HFC network. Typically VoP is higher with cables of this size.

    It all depends on the frequency though. The difference in behavior between a signal at 55 MHz or 750 MHz is enormous.


    But the sources I read suggested that the insulation actually slowed down the transmission speed depending on the dialectic properties of the material.
    I'm not sure if you mean insulation, as in a jacket, or if you're referring to the dielectric material.

    If it's the former, it likely has some effect, but I assume it to be rather negligible. It is rational to think that a thinner jacket would slow, or at a minimum, interfere, with the transmitted signals. As jackets or braid(metal strands located between the jacket and dielectric) gets thinner it allows more signals to egress and ingress, generating harmonics, ergo, distortions (Composite Second Order, Composite Triple Beats, Low Carrier to Noise figures). Generally signals bounce between the copper core (which is only a copper jacket over a piece of aluminum) of a coaxial cable and the aluminum shielding. In a perfect world, signals shouldn't even reach the jacket or insulation.

    If your question refers to the latter, dielectric material plays an essential role in determining VoP for coax, not so much for fiber because, well, it's all glass.
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    Forum Radioactive Isotope mitchellmckain's Avatar
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    Quote Originally Posted by CaveatLector
    If your question refers to the latter, dielectric material plays an essential role in determining VoP for coax, not so much for fiber because, well, it's all glass.
    The article I was trying to understand started by talking about separate wires but I guess the coaxial cable better controls the dialetric and capacitance between the incomming and outgoing lines by using the coaxial configuration. I guess parallel wires are more susceptible to interference with the electrical properties of nearby materials.
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    Quote Originally Posted by mitchellmckain
    Quote Originally Posted by CaveatLector
    If your question refers to the latter, dielectric material plays an essential role in determining VoP for coax, not so much for fiber because, well, it's all glass.
    The article I was trying to understand started by talking about separate wires but I guess the coaxial cable better controls the dialetric and capacitance between the incomming and outgoing lines by using the coaxial configuration. I guess parallel wires are more susceptible to interference with the electrical properties of nearby materials.
    I think there are two different discussions here.
    Electricity or electrical signals, i.e. RF, needs only a complete circuit to operate (I’m positive you know this). You don't have to have signals flowing in opposite directions causing inductance or eddy currents.

    With cable and RF, signals do flow in opposite directions, but not in a manner consistent with what you've been describing. Downstream signals flow generally from 55.25 MHz to 7500-850 MHz and upstream, sometimes called the reverse or return, flows counter to the downstream, but through a different part of the frequency spectrum-5 to 42 MHz. There is a large buffer between downstream and upstream, so generally the signals are completely independent of each other.

    I think your sources are talking about the dielectric material only. Capacitance plays a major role there, but "incoming and outgoing" signals don't distort each other. Interference comes mainly from noise ingressing through the cables. I'm not sure that twin leads are more heavily insulated, I'd say it would vary between each specific type, and there are virtually hundreds.
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  10. #9  
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    Hmm, should have studied english in stead of physics. I can't make sence of it all.. what was it about again. :?

    And why does electricity travel faster in Air insulated wires than in rubber insulated.

    Does it stick to the sides, of does air have a positive effect. maybe it cooles better or something?¿?
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