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The speed of electricity and the loses

  1. Jan 22, 2013 #1
    Hi im "new" here.

    Uh so the speed of electricity in copper is about 95-97% of the speed of light.

    Now to clarify. That is the speed it uses (say DC) from one place to another.

    And the reason for the loses in speed is due to the electrons having mass. So when one bumps the other the other takes some time to get moving. Is this correct?

    So.. those five percents it loses in speed.. thats energy, does it go over to heat? hence the slower speed in lesser leaders -> more heat generated.

    I see no other explanation.
     
  2. jcsd
  3. Jan 22, 2013 #2

    Simon Bridge

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    Welcome to PF;

    electrons in a wire move surprisingly slowly. Don't know what you mean by "electricity".
    electrons do lose energy as the travel, but they start out slow as well.

    So - to understand your statements we need to know where you are getting your figures from.
     
  4. Jan 22, 2013 #3
  5. Jan 22, 2013 #4

    jim hardy

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    check this link, which was referenced at the one you just posted.
    http://en.wikipedia.org/wiki/Telegrapher's_equations

    in paragraph "Role of different components" is an animated graphic that might be worth a thousand words.
    Observe how fast the wave moves compared to the actual charge carriers.
    It's like shouting down a tube - you don't move much air. But the minute rarefaction and compession of the air goes at speed of sound.

    any help?

    Now have at those equations....

    old jim
     
  6. Jan 22, 2013 #5

    dlgoff

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  7. Jan 22, 2013 #6
    Also keep in mind Rf frequencies as well as DC signal can be delayed by interence with other frequencies (cross talk )
     
  8. Jan 22, 2013 #7
    Also keep in mind Rf frequencies as well as DC signal can be delayed by interence with other frequencies (cross talk ) . Also in the case of RF there is also reflective wave effects. Factors such as these create propogation delays in signals. Dialectric strength also plays an important factor
     
  9. Jan 22, 2013 #8

    jim hardy

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    i dont think so.


    the reason for the variation in speed is same as for speed of sound,
    speed of sound depends on what it's moving through and in any medium it's √(stiffness/density)

    electric waves have speed in proportion to a similar ratio,
    where stiffness and density are mechanical analogues to electrical characteristics of the wire and the medium surrounding the wire.
    Geometry has an effect too.

    95% to 99% is typical for air insulated transmission lines
    60% to 80% for plastic insulated.


    See if this helps any:
    http://en.wikipedia.org/wiki/Wave_propagation_speed
     
  10. Jan 23, 2013 #9
    Speed figure is a bit high, depending on the geometry of the conductor, but 70% of c seems a workable figure. This is the speed of propagation of the electromagnetic wave - the fields of electrons are mutually repulsive so push one at one end of the wire just a little and that push is propagated down the wire by each electron moving just a little bit along the wire, repelled from the previous by its field repulsion. Each individual electron moves only a little to create a wave that travels at speed. The electrons don't move fast at all.

    The push is lossless. No energy is dissipated. The energy losses come from interactions between the electrons and the metal matrix. Hence in a superconductor where there are no lossy interactions between the electrons and the matrix there are no losses at all.
     
  11. Jan 23, 2013 #10

    Simon Bridge

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    Well there is an answer in there for almost every reasonable take on OPs question.
    @MatsNorway: any of that help?
     
    Last edited: Jan 23, 2013
  12. Jan 23, 2013 #11
    Lol Im not the OP. MatsNorway is.
     
  13. Jan 23, 2013 #12

    Simon Bridge

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    So edited just failed reading/comprehension 101 :blush:
    If we both delete these responces, the mistake will be lost to history?
     
  14. Jan 23, 2013 #13
    Im out in the field so Id have to figure out how to do so from my phone app lol
     
  15. Jan 24, 2013 #14
    What is a bit high? the article on Wikipedia about wave propagation speed claimed 95-99% lets assume ideal conditions. Who would be a naked solid wire in a lab where that number would pop up.

    How something not leading electrisity like rubber insulation can affect the results i dont really grasp.


    Does the drop in speed comes from a longer way to go? as it can`t go in a straight line in the copper but must go via sertain structure ends/shapes.

    So if the resistance does not provide a drop in speed.. what does the resistance do to the electricity wave/push as you called it.
     
    Last edited: Jan 24, 2013
  16. Jan 24, 2013 #15

    jim hardy

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    The delay comes from inductance and capacitance, as explained in the wiki link.

    Inductance and capacitance oppose flow of current, but differently than resistance.

    Resistance turns energy into heat so it disappears from the wire.

    Inductance and capacitance merely impede its movement of energy, delaying it.
    Insulation has capacitive properties different from air , and straight wire has inductance. That's why geometry and insulating material have an effect.

    You really ought to study the basics . Try this guy's explanations.

    http://amasci.com/elect/elefaq.html
     
  17. Jan 24, 2013 #16
    We always used a starting figure of 70% or 2/3 of the speed of light in a good cable. This is the speed of propagation of the electromagnetic wave, the speed of the electrons is tiny. Think of a row of ballbearings representing electrons. Push one end of the row slowly, the ballbearing at the other end moves immediately. So although the individual ballbearings move slowly the push is felt at the other end very quickly. Now think of the ballbearings as electrons and the push as the electromagnetic wave.

    The speed is a function of the geometry of the cable/transmission line and the properties of materials used, including resistance. Loss of energy as the wave travels does not affect its speed, all you get is a smaller wave travelling at the same speed. In other words the energy losses simply reduce the wave amplitude. Losses may be from resistance in the conductors and from radiation.

    Non-conductive materials can react with electrical and magnetic fields. The molecules in some materials can twist to follow an electric field, then when the field is reversed switch the other way. This has two primary effects - it tends to reduce the strength of the field because it tends to partially cancel it, and the there may be hysteresis which converts the electromagnetic energy into heat.
     
  18. Feb 18, 2013 #17
    Thank you for the help guys.

    I made a new thread regarding mechanical discussion at work. check it out.
     
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