# What is the speed of electricity ? **URL:** \ **Category:** Factual Questions\ **Created:** [September 20, 2001, 1:28pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781 "2001-09-20T13:28:10Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![berdollos](https://avatars.discourse-cdn.com/v4/letter/b/ed8c4c/32.png) [@berdollos](https://boards.straightdope.com/u/berdollos)\ **Post date:** [September 20, 2001, 1:28pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/1 "2001-09-20T13:28:10Z")
That is my question. ---
**Author:** ![NutMagnet](https://avatars.discourse-cdn.com/v4/letter/n/ea5d25/32.png) [@NutMagnet](https://boards.straightdope.com/u/NutMagnet)\ **Post date:** [September 20, 2001, 1:36pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/2 "2001-09-20T13:36:28Z")
The speed of current approximates the speed of light. The speed of electricity is very slow (3 inches per hour). See [http://www.amasci.com/miscon/speed.html](http://www.amasci.com/miscon/speed.html) ---
**Author:** ![DVous\_Means](https://avatars.discourse-cdn.com/v4/letter/d/9fc29f/32.png) [@DVous\_Means](https://boards.straightdope.com/u/DVous_Means)\ **Post date:** [September 20, 2001, 1:36pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/3 "2001-09-20T13:36:35Z")
I have always worked on the assumption that it was the same as the speed of light, but I’m prepared to be proved wrong. ---
**Author:** ![lucwarm](https://avatars.discourse-cdn.com/v4/letter/l/e19adc/32.png) [@lucwarm](https://boards.straightdope.com/u/lucwarm)\ **Post date:** [September 20, 2001, 1:39pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/4 "2001-09-20T13:39:35Z")
You can conceive of electric current as an electromagnetic wave travelling around the conductor. Under this model, the speed of electricity is approximately the speed of light, depending on the properties of the insulation of the wire. (And note that the actual electrons aren’t moving much at all - think of the speed of water molecules in the ocean versus the speed of a wave) See also: [http://www.straightdope.com/classics/a940722b.html](http://www.straightdope.com/classics/a940722b.html) ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [September 20, 2001, 1:53pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/5 "2001-09-20T13:53:08Z")
In free space, an electromagnetic wave in a vacuum travels at very close to one foot per nanosecond. This is a handy rule of thumb for those of us in the US. In coaxial cable, the dielectric material inside it is what determines the speed, typically slowing it down by a factor of about 0.7. In other kinds of wiring, it’s less precise, but it will be slowed down around the same amount. ---
**Author:** ![Sea\_Sorbust](https://avatars.discourse-cdn.com/v4/letter/s/6f9a4e/32.png) [@Sea\_Sorbust](https://boards.straightdope.com/u/Sea_Sorbust)\ **Post date:** [September 20, 2001, 2:30pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/6 "2001-09-20T14:30:31Z")
I at last begin to understand why I flunked ElectroMagnetics twice and almost a third time (–I’m convinced that the only reason I passed the third try was that the Physics department cringed at the thoughts of my showing up for yet a 4th time). **NutMagnet** , is that [amasci.com](http://amasci.com) ([eskimo.com](http://eskimo.com)) link accurate? Do they really know their stuff? (It sounds as if they do.) Whew! Not to hijack a thread, but does **anybody** really understand what goes on inside an EM field generated by “oozing” electrons? ---
**Author:** ![grimpixie](https://avatars.discourse-cdn.com/v4/letter/g/ecb155/32.png) [@grimpixie](https://boards.straightdope.com/u/grimpixie)\ **Post date:** [September 20, 2001, 2:34pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/7 "2001-09-20T14:34:07Z")
[http://boards.straightdope.com/sdmb/showthread.php?postid=1630049#post1630049](http://boards.straightdope.com/sdmb/showthread.php?postid=1630049#post1630049) ---
**Author:** ![Nyrath](https://avatars.discourse-cdn.com/v4/letter/n/919ad9/32.png) [@Nyrath](https://boards.straightdope.com/u/Nyrath)\ **Post date:** [September 20, 2001, 2:42pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/8 "2001-09-20T14:42:02Z")
> [@](#): > > \*Originally posted by CurtC \* > **In free space, an electromagnetic wave in a vacuum travels at very close to one foot per nanosecond. This is a handy rule of thumb for those of us in the US.** The legendary Admiral Grace Hopper, at her lectures, would often hand out “nanoseconds”. These were lengths of wire cut to about a foot. She would compare this to a microsecond, which would be the equivalent of a coil of wire about a thousand feet long. But she would hammer home the fact that even a nanosecond was a tangible amount, and computer programmers should not waste them. ---
**Author:** ![Popup](https://avatars.discourse-cdn.com/v4/letter/p/94ad74/32.png) [@Popup](https://boards.straightdope.com/u/Popup)\ **Post date:** [September 20, 2001, 2:47pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/9 "2001-09-20T14:47:59Z")
> [@](#): > > \*Originally posted by Nyrath \* > **The legendary Admiral Grace Hopper, at her lectures, would often hand out “nanoseconds”. These were lengths of wire cut to about a foot.** When I worked at CERN many cables were marked, not with their physical length, but with their delay. (this was mainly coax, and the signal speed was more or less [sup]2[/sup]/[sub]3[/sub]c, so there would be about 5ns/m.) ---
**Author:** ![toadspittle](https://avatars.discourse-cdn.com/v4/letter/t/c0e974/32.png) [@toadspittle](https://boards.straightdope.com/u/toadspittle)\ **Post date:** [September 20, 2001, 2:53pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/10 "2001-09-20T14:53:16Z")
Wow. I find all of that really cool, for some reason. ---
**Author:** ![lucwarm](https://avatars.discourse-cdn.com/v4/letter/l/e19adc/32.png) [@lucwarm](https://boards.straightdope.com/u/lucwarm)\ **Post date:** [September 20, 2001, 3:33pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/11 "2001-09-20T15:33:06Z")
> [@](#): > > \*Originally posted by tc \* > \*\* > When I worked at CERN many cables were marked, not with their physical length, but with their delay. (this was mainly coax, and the signal speed was more or less [sup]2[/sup]/[sub]3[/sub]c, so there would be about 5ns/m.) \*\* So make sure you equalize the length of your speaker cables. 😉 ---
**Author:** ![casdave](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@casdave](https://boards.straightdope.com/u/casdave)\ **Post date:** [September 20, 2001, 5:27pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/12 "2001-09-20T17:27:00Z")
…and now to murk things up somewhat. Electrons in circuits travel neither far nor fast, it’s the energy that is transferred that travels fast. Each electron carries a charge which its dumps onto the next in line, it’s a little like the desktop toy endless swinging balls, the balls stay still but the kinetic energy travels from one end to the other. Another analogy might be in a hydraulic system where the pipework is filled with oil, a piston operates to push the column of oil and (assuming no pipe flexion or compressibility) instantly oil is forced out the other end which can be put to work, the oil hasn’t actually travelled from the piston all the way through the tubes, just the force of the displacing piston, so in that sense the energy travels far faster than the oil itself. This is very loose description and has a great many holes in it because some sub-atomic parts can also be waves and particles partly dependant on measuring techniques, electron have a tendency to migrate, however, they do travel along path one would expect and also against it too. Thing is that even if there was not an external source of voltage potential, electrons can drift around within a material. Most of what has been described by previous posters relates to electro-magnetic waves and while this is an electrical force it is not every electrical force.(ish) ---
**Author:** ![Sea\_Sorbust](https://avatars.discourse-cdn.com/v4/letter/s/6f9a4e/32.png) [@Sea\_Sorbust](https://boards.straightdope.com/u/Sea_Sorbust)\ **Post date:** [September 20, 2001, 5:44pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/13 "2001-09-20T17:44:08Z")
So if the electrons are moving really sloowly, and there’s nothing else physical moving around inside the wire, what causes the resistance and the heat-energy that makes light? And if it’s all because of the “current” (which somehow I always thought were the electrons—or a sequence of pool-ball-like bumpings of one electron into another, like a many-car rear-ender), which is a field(yes? no?), why does the speed down the wire vary? Does all this mean that the answer to the OP is: “Depends.”? And if so, what are the various factors involved that influence the speed of the “electricity”? And is what **casdave** says, that the electrons don’t travel very far (ever?), correct? Don’t they HAVE TO go from one electrode to the other?? (Thence to cycle back around again and again?) 😕 ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [September 20, 2001, 6:20pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/14 "2001-09-20T18:20:40Z")
In her later years, she would hand out picoseconds. They were little packets of pepper. ---
**Author:** ![Chas.E](https://avatars.discourse-cdn.com/v4/letter/c/e99b99/32.png) [@Chas.E](https://boards.straightdope.com/u/Chas.E)\ **Post date:** [September 20, 2001, 6:31pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/15 "2001-09-20T18:31:34Z")
> [@](#): > > \*Originally posted by tc \* > \*\*When I worked at CERN many cables were marked, not with their physical length, but with their delay. (this was mainly coax, and the signal speed was more or less [sup]2[/sup]/[sub]3[/sub]c, so there would be about 5ns/m.) \*\* I once read an article by Seymore Cray about the design limitations of supercomputers, he also asserted that an electrical charge only travels at [sup]2[/sup]/[sub]3[/sub]c in copper wire. ---
**Author:** ![Ring](https://avatars.discourse-cdn.com/v4/letter/r/6a8cbe/32.png) [@Ring](https://boards.straightdope.com/u/Ring)\ **Post date:** [September 20, 2001, 7:06pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/16 "2001-09-20T19:06:36Z")
I’m sure this is _much_ more than you wanted to know but here it is anyway. Please accept my apologies. As stated above, the energy is transported in the electric and magnetic fields _outside_ the conductor at the speed of light in copper = 1 / sqrt( permittivity\*permeability). Inside the copper the wave speed is about 400 m/s assuming the source is around 1 MHz. The fields outside the conductor travel at relativistic speeds, but there is a very abrupt transition at the surface of the conductor to the lower speed. It’s not discontinuous but very nearly so. The energy flow is determined by the Poynting vector which is proportional to the cross product of the E field with the B field. Since the E field is radial and the B field is circumferential the PV points in the direction of the current flow. (Right hand rule.) On the other hand, the E field _inside_ the conductor (or on the surface) is in the direction of the current flow so power would only flow into the conductor (this is what causes the I[sup]2[/sup]R heating loses.) ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [September 20, 2001, 8:23pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/17 "2001-09-20T20:23:20Z")
Chas E. wrote: > [@](#): > > I once read an article by Seymore Cray about the design limitations of supercomputers, he also asserted that an electrical charge only travels at 2/3c in copper wire. It may be a minor point, but it’s interesting, that the speed of propagation depends not on the metal conductor, but on the insulating material around it. The speed of light in a non-magnetic material is slowed by one over the square root of the relative electrical permittivity. The permittivity is around 2 for most insulators, so the speed is around 0.7c. Water has a permittivity of 81, so a cable using water as the insulator would have a propagation speed of around 0.11c. ---
**Author:** ![Sea\_Sorbust](https://avatars.discourse-cdn.com/v4/letter/s/6f9a4e/32.png) [@Sea\_Sorbust](https://boards.straightdope.com/u/Sea_Sorbust)\ **Post date:** [September 21, 2001, 5:50pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/18 "2001-09-21T17:50:31Z")
“[The] speed of propagation depends not on the metal conductor, but on the insulating material around it”? **CurtC** , I don’t know about **berdollos** , but I think that I’ll give up on _ever_ being able to understand the answer to even a simple ElectroMagnetic question like the OP: “What is the speed of electricty?”. ---
**Author:** ![bbeaty](https://avatars.discourse-cdn.com/v4/letter/b/c0e974/32.png) [@bbeaty](https://boards.straightdope.com/u/bbeaty)\ **Post date:** [September 21, 2001, 9:56pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/19 "2001-09-21T21:56:27Z")
> [@](#): > > \*Originally posted by Sea Sorbust \* > **So if the electrons are moving really sloowly, and there’s nothing else physical moving around inside the wire, what causes the resistance and the heat-energy that makes light?** The resistance is really fierce. It’s like pumping tar through a stack of window screens. Even though the electron-stuff flows slowly, it creates lots of heat when it “rubs against” the electrical friction of the light bulb filament. > [@](#): > > **And if it’s all because of the “current” (which somehow I always thought were the electrons—or a sequence of pool-ball-like bumpings of one electron into another, like a many-car rear-ender), which is a field (yes? no?), why does the speed down the wire vary?** Yes, electric current is just a flow of electric charges (electrons.) But note that there are TWO speeds: the speed of electron flow, and the speed of waves along the column of electrons. Analogy: pull on the end of a long chain, and the far end of the chain will jerk at nearly the same time. The chain itself moves slowly towards you, but the “ripple” moves very fast in the opposite direction. > [@](#): > > **And is what casdave says, that the electrons don’t travel very far (ever?), correct? Don’t they HAVE TO go from one electrode to the other?? (Thence to cycle back around again and again?)** Here’s the big secret: electric circuits are like slow-moving drive belts. The electrons are like the rubber molecules in the belt. Wires are already full of electrons all the time (in fact, all metals are full of electrons.) Hook a bunch of wires into a big circle, and you’ve created a drive belt. Install an electron pump (a generator), and you can make the entire “belt” move along. Add a pinch-point, and you’ve got yourself an electric heater. When you start the pump, the belt moves very slowly, yet the entire belt begins moving at almost the same time. More about this at:\ ELECTRICITY MISCONCEPTIONS [http://amasci.com/miscon/elect.html](http://amasci.com/miscon/elect.html) [http://amasci.com/elect/elefaq.html](http://amasci.com/elect/elefaq.html) \ ---
**Author:** ![Sea\_Sorbust](https://avatars.discourse-cdn.com/v4/letter/s/6f9a4e/32.png) [@Sea\_Sorbust](https://boards.straightdope.com/u/Sea_Sorbust)\ **Post date:** [September 25, 2001, 3:57pm UTC](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781/20 "2001-09-25T15:57:10Z")
What you say, **bbeaty** , is very believable. Thank you very much. 🙂 I shall reade more (I like your site, BTW). [Next page](https://boards.straightdope.com/t/what-is-the-speed-of-electricity/82781.md?page=2)