3 ms·

u/cogman10 comment reads to me as if they are saying that EM radiation and light travel at different speeds.

Tuna-Fish 2y ago
They travel at the same speed, in the same medium. c is the speed of light in a vacuum, all EM radiation travels slower in any other medium. The complicating factor here is that when you have electricity flowing in a wire, the fields are generally mostly outside the conductor, not in it. That is, the signal propagation delay depends more in what you are using as an insulator around wire than the material of the wire. This has had practical consequences in the past; if you replace the insulating jacket of one wire in a twisted pair with a slightly different material, on long runs it will ruin your signal.
mr_toad 2y ago
EM radiation, whether radio or visible light is photons, and photons only have one speed. However, electrical conduction is the movement of electrons, not photons.
- Tuna-Fish 2y ago
  > EM radiation, whether radio or visible light is photons Is the only part that's not wrong in your post. Photons only have one speed in empty space. They slow down when traveling through any medium other than vacuum. > However, electrical conduction is the movement of electrons, not photons. Electrons move because they influence each other through their fields, which are transmitted by photons. Electrical conduction happens at the speed of the fields, not at the speed of the electrons. When you push one more electron into one side of a conductor, an electron flows out the other side when the fields reach the other side, not when the electron does. (As an analogy, consider a rubber hose full of steel balls. When you slowly push an additional ball in from one side, another ball starts to fall out of the other side as you push the first ball in, perceptually instantenously⁰, regardless of the speed you are pushing the new ball in. (0): After a delay of (length of tube)/(speed of sound in steel)
  - tatjam 2y ago
    I'm not a physicist, but as far as I know, outside of general relativity electromagnetic perturbations always travel at the speed of light (i.e. to affirm that photons always travel at c is correct). It's only after the fields interact with electrical charges (atoms and their electrons for example) that a secondary field is induced as these charges begin to oscillate. This field will add over the original field, "shielding" an external observer from the original oscillation and apparently slowing down the propagation of electromagnetic waves. There's a very good video by 3Blue1BRown that explains this kind of weird concept way better than I could: https://www.youtube.com/watch?v=KTzGBJPuJwM https://www.youtube.com/watch?v=KTzGBJPuJwM

They travel at the same speed, in the same medium. c is the speed of light in a vacuum, all EM radiation travels slower in any other medium. The complicating factor here is that when you have electricity flowing in a wire, the fields are generally mostly outside the conductor, not in it. That is, the signal propagation delay depends more in what you are using as an insulator around wire than the material of the wire. This has had practical consequences in the past; if you replace the insulating jacket of one wire in a twisted pair with a slightly different material, on long runs it will ruin your signal.

mr_toad 2y ago

EM radiation, whether radio or visible light is photons, and photons only have one speed. However, electrical conduction is the movement of electrons, not photons.

Tuna-Fish 2y ago
> EM radiation, whether radio or visible light is photons Is the only part that's not wrong in your post. Photons only have one speed in empty space. They slow down when traveling through any medium other than vacuum. > However, electrical conduction is the movement of electrons, not photons. Electrons move because they influence each other through their fields, which are transmitted by photons. Electrical conduction happens at the speed of the fields, not at the speed of the electrons. When you push one more electron into one side of a conductor, an electron flows out the other side when the fields reach the other side, not when the electron does. (As an analogy, consider a rubber hose full of steel balls. When you slowly push an additional ball in from one side, another ball starts to fall out of the other side as you push the first ball in, perceptually instantenously⁰, regardless of the speed you are pushing the new ball in. (0): After a delay of (length of tube)/(speed of sound in steel)
- tatjam 2y ago
  I'm not a physicist, but as far as I know, outside of general relativity electromagnetic perturbations always travel at the speed of light (i.e. to affirm that photons always travel at c is correct). It's only after the fields interact with electrical charges (atoms and their electrons for example) that a secondary field is induced as these charges begin to oscillate. This field will add over the original field, "shielding" an external observer from the original oscillation and apparently slowing down the propagation of electromagnetic waves. There's a very good video by 3Blue1BRown that explains this kind of weird concept way better than I could: https://www.youtube.com/watch?v=KTzGBJPuJwM https://www.youtube.com/watch?v=KTzGBJPuJwM