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https://www.youtube.com/watch?v=jbi7gJTPSXk

Please check 1:33.

Many people said that all the electrons are just shifted at the same time when a current flows in the wire. So electricity can move with the speed of light.

If I have $3\times 10^8m$ wire and force a current at one end of that wire, it will take $1s$ for electricity to flow. In case of $6\times 10^8m$ wire, it will take $2s$. Why does it take more time in case of the longer wire? If actual electrons don't need to flow to the other end of the wire, why is the velocity of electricity limited to velocity of light?

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  • $\begingroup$ Because to shift every electron at once you have to change electric potential at once. But changes in em field take time $\endgroup$ – kakaz Dec 22 '19 at 9:59
  • $\begingroup$ Thank you for your answer. By any chance, is there any book or paper which deals with the actual velocity of electric potential in the ideal conductor? $\endgroup$ – superkappy Dec 22 '19 at 10:13
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    $\begingroup$ To have your formulas correctly displayed like $3\cdot10^8m$ you can check this site: math.meta.stackexchange.com/questions/5020/… $\endgroup$ – NiveaNutella Dec 22 '19 at 11:12
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You think of the electrons as a bulk material, which we are able to shift at once. This is not true. Rather think of them as small balls, which bounce into each another: The electrons in the wire bounce into each another all the time, even if you are not applying a voltage. Without voltage we don't get a current, because they shift as often to the left as they shift to the right. If you apply a voltage across the wire, this changes. There exists a small difference between shifting to the left and shifting to the right.

The key message of this picture is, that the shifting needs time. Here is an animation for sound waves (lower picture): The wave needs some time to travel from one end to the other, but the particles stay mainly at the same position. While this comparison has many flaws, I hope it helps you to understand "bouncing into each another" sentence.

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  • $\begingroup$ Thank you for your answer. Please, check the followings. www1.astrophysik.uni-kiel.de/~hhaertel/PUB/Voltage-PdN.pdf Fig.6 matterandinteractions.org/wp-content/uploads/2016/07/… Fig.8 According to many papers and text books, there are ring type excess surface charges in the wire to build the internal electric potential when a current flows in that wire. Your "bouncing into each another" means both building internal ring type excess charges on the surface and domino-like sequential electron shift simultaneously? or just one between two phenomena? $\endgroup$ – superkappy Dec 26 '19 at 16:30
  • $\begingroup$ Did you look at the video in my answer? My answer has nothing to do with "ring type excess charges on the surface", and neither does Andrews. It's a simple picture which intuitively explains why electricity travels with approx. the speed of light. $\endgroup$ – Semoi Dec 26 '19 at 16:49
  • $\begingroup$ I checked that video. I found 4 type answers to electricity speed problem. 1. Photon related explanation. 2. All electrons are shifted in the wire but changes in EM field take time. 3. Excess surface charge makes potential distribution in the wire and that potential shifts all the electrons in the wire. 4. Electron-to-electron coordination via communication. Your answer and Andrew's are type 4 answers. I just thought above four type answers should have a thread of connection. For example, due to the electron push, excess surface charges are distributed with the speed of light in the wire. $\endgroup$ – superkappy Dec 27 '19 at 7:20
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A battery or something gives a push to an electron at one end of a wire. This electron pushes its neighbours, then they push their neighbours, and so on. Each such push is conveyed via the electroagnetic field associated with any given electron. The speed at which the push propagates is the speed at which the electromagnetic field around each electron can adjust to the movement of its electron. That speed is the speed of light.

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