Electricity Speeds: How Fast Does It Move?

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    Electricity Speed
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Discussion Overview

The discussion revolves around the speed of electricity, particularly in the context of lightning and electrical signals in conductors. Participants explore various aspects of how electricity moves, including the speed of electrons, the propagation of electric fields, and the complexities of lightning phenomena.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants note that the speed of electrons in a wire is very slow, around a few mm/s, while the speed of the electric field is a large fraction of the speed of light.
  • Others mention that lightning involves various stages, with estimates of its speed reaching several 100,000 mph, but the visible streak of lightning can appear instantaneously or move slowly depending on conditions.
  • A participant questions the apparent discrepancy in lightning speed, suggesting that the visible streak may be influenced by atmospheric conditions and the duration of the flash rather than the speed of propagation.
  • Some participants discuss the analogy of electrons acting like a Newton's Cradle, where the signal is transmitted quickly despite the slow movement of individual electrons.
  • It is mentioned that signals in coaxial cables can travel at speeds between 0.66 to over 0.9 times the speed of light, depending on the dielectric material used.
  • There is a challenge regarding the claim of electron speeds in wires, with references to electron drift velocity and the propagation of electric fields, which can be around 98% of the speed of light in free air.
  • Participants highlight that observed propagation delays in digital circuits contradict the idea of slow electron speeds, emphasizing that signals propagate much faster than the individual movement of electrons.

Areas of Agreement / Disagreement

Participants express differing views on the speed of electricity, particularly regarding the movement of electrons versus the propagation of electric fields. There is no consensus on the specifics of these speeds or the implications for lightning phenomena.

Contextual Notes

Some claims depend on definitions of speed and context, such as the distinction between electron drift velocity and signal propagation speed. The discussion also touches on the complexities of lightning, which may not be fully understood.

leroyjenkens
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How fast does electricity move? It seems to move at different speeds when in lightning form. Like sometimes a bolt of lightning will be instant and then other times you can see it streaking kinda slowly across the sky.
 
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Like a lot pf physics - it depends what you mean!

The speed of electrons moving a long a wire is very slow - a few mm/s, the speed of the electric field moving along a wire is a large fraction of the speed of light.

Lightning is a little more complicated, there are lots of stages in a lightning strike, the leader current, the return current, the ionization etc - but several 100,000 mph would be a reasonable estimate.
 
Like a lot pf physics - it depends what you mean!
True. What I'm talking about is the visible streak that the lightning creates. Sometimes it's so fast, it looks like the entire bolt of lightning appears instantly. Then other times I can see the visible streak go across the sky. I was just wondering why there was a discrepancy.
The speed of electrons moving a long a wire is very slow - a few mm/s, the speed of the electric field moving along a wire is a large fraction of the speed of light.
It's weird, so the electrons actually don't move that fast, but they act kind of like a Newton's Cradle and thus the signal gets sent quickly?
 
Check out this wikipedia article on lightning:
http://en.wikipedia.org/wiki/Lightning

Although it does not address your question directly, this article suggests a lot: namely, we still have a LOT to learn about lightning. The apparent different types of lightning, positive, negative,ball, cloud to ground,cloud to cloud, etc, suggests a lot we do not understand. It would seem possible that leaders in different types of atmosphere, say varying temperatures, humidities, varying degrees of particles in the air,etc might also affect lighting propagation As is evident in the article, many lightning activities are so quick they are largely imperceptible to our senses.

Also note the description of ball lightning which is believed to last longer than other "types"..so what you may see is not a difference is the speed of propagation but in the duration of the flash.
 
leroyjenkens said:
so the electrons actually don't move that fast, but they act kind of like a Newton's Cradle and thus the signal gets sent quickly?
Yes - excellent analogy.
 
Signals move in coaxial cables as a TEM (transverse electric magnetic) waves at about 0.66 to over 0.9 times the speed of light. The velocity of the signal depends primarily on the dielectric constant of the dielectric between the inner and outer copper conductors.
Stanford Linear Accelerator Center (SLAC) produces beams of electrons in vacuum at about 0.999999+ times the speed of light.
 
Electron's move at mm/s in a wire? To a rough approximation of free electrons in an infinite, vanishing, periodic lattice do we not get that electrons go about 10% of c?
 
Not to mention the observed propagation delays in digital circuits would not be consistent with such a slow speed
 
maverick_starstrider said:
Electron's move at mm/s in a wire? To a rough approximation of free electrons in an infinite, vanishing, periodic lattice do we not get that electrons go about 10% of c?

No. Look up electron drift velocity.

As previously noted above, the speed of electrical signals you observe is not due to the motion of the electrons in a conductor but the propagation of the electric field in the space around the conductor. The velocity of this propagation is dependent upon the speed of light through the medium around the conductor; for free air this is about 98% c while for typical plastic insulations it varies between 50 and 75% c.
 
  • #10
maverick_starstrider said:
Not to mention the observed propagation delays in digital circuits would not be consistent with such a slow speed

Signal propagation speed is only very loosely related to electron propagation speed. The electrons move more like a train then individual cars. When a signal is applied it is felt by all electrons in the conductor. Signals propagate much faster then the individual electrons.
 

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