2 ms·

(I had to create an account to respond to this) "Light" and "electricity" only travel at the same speed in a vacuum. Neither fibre nor copper wire could reason

by pugz 13y ago

(I had to create an account to respond to this) "Light" and "electricity" only travel at the same speed in a vacuum. Neither fibre nor copper wire could reasonably be considered a vacuum; they have different propagation speeds. Also, we are far removed from "gen 1 of fibre", which was developed in 1970, i.e. 43 years ago. If anything, we're currently developing "fifth gen" fibre optics communications. Everything else you said is spot on, though.

retrogradeorbit 13y ago
Actually zmmmmm is correct about the speeds. The drift velocity of electrons in a conductor is quite low. Somewhere around 1 meter per second (its been a long time since my physics degree so it may not be exactly 1ms-1). But what happens when you close a circuit of a conductor across a potential difference is an electric field is set up surrounding the conductor. This electric field accelerates all the electrons in the conductor at once. This is why even though the drift velocity of an electron in a conductor is very low, when you switch on a light switch the bulb lights immediately. The propagation of the electric field is at the speed of light (its electromagnetism). So "electrons" move slowly but "electricity" moves at the speed of light. Update: found a wikipedia page on it: http://en.wikipedia.org/wiki/Speed_of_electricity http://en.wikipedia.org/wiki/Speed_of_electricity
- pugz 13y ago
  That's true, but light only travels at ~0.67c in a fibre optic cable. That's why I mentioned that fibre optic cables and copper wires are not vacuums.
  - retrogradeorbit 13y ago
    According to wikipedia, electric field propagation through unshielded copper is 0.95c to 0.97c. Electric field propagation through standard coaxial cable is 0.66c.
    - pugz 13y ago
      Hence why zmmmmm was incorrect about the speeds: electricity in the copper wires is travelling faster than light in the fibre optic cables. zmmmmm didn't mention drift velocity, but that wasn't really related to his point.
- Wingman4l7 13y ago
  Thanks for the refresher -- I recall being taught this in HS physics but I've never repeated it because I didn't want to look like an idiot trying to explain how "electrons" don't move at the speed of light.

by pugz 13y ago

retrogradeorbit 13y ago

Actually zmmmmm is correct about the speeds. The drift velocity of electrons in a conductor is quite low. Somewhere around 1 meter per second (its been a long time since my physics degree so it may not be exactly 1ms-1). But what happens when you close a circuit of a conductor across a potential difference is an electric field is set up surrounding the conductor. This electric field accelerates all the electrons in the conductor at once. This is why even though the drift velocity of an electron in a conductor is very low, when you switch on a light switch the bulb lights immediately. The propagation of the electric field is at the speed of light (its electromagnetism). So "electrons" move slowly but "electricity" moves at the speed of light. Update: found a wikipedia page on it: http://en.wikipedia.org/wiki/Speed_of_electricity http://en.wikipedia.org/wiki/Speed_of_electricity

pugz 13y ago
That's true, but light only travels at ~0.67c in a fibre optic cable. That's why I mentioned that fibre optic cables and copper wires are not vacuums.
- retrogradeorbit 13y ago
  According to wikipedia, electric field propagation through unshielded copper is 0.95c to 0.97c. Electric field propagation through standard coaxial cable is 0.66c.
  - pugz 13y ago
    Hence why zmmmmm was incorrect about the speeds: electricity in the copper wires is travelling faster than light in the fibre optic cables. zmmmmm didn't mention drift velocity, but that wasn't really related to his point.
Wingman4l7 13y ago
Thanks for the refresher -- I recall being taught this in HS physics but I've never repeated it because I didn't want to look like an idiot trying to explain how "electrons" don't move at the speed of light.