# Is electricity instantaneous?

My question is basically what exactly is electricity? I've simply been told before that it's a flow of electrons, but this seems too basic and doesn't show that electricity is instant. What I mean is turning a switch has no delay between that and a light coming on. Is it really instantaneous? Or is it just so fast that we don't notice it?

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"I've simply been told before that itsa flow of electrons, but this seems to basic and does show that electricity is instant." Why would this mean that electricity is "instantaneous" ? –  Cedric H. Nov 8 '10 at 10:48
Sorry I meant doesn't rather than does. –  Jonathan. Nov 9 '10 at 8:20

It's just so fast you don't notice it. You won't see the effect of the travel time in something like turning on a light, because your eyes aren't fast enough to register the delay, but if you do even moderately precise experiments involving signal transmission and look at it on an oscilloscope, you will find that the travel time is easily measurable. The speed of signal propagation is close to that of light, or about a foot per nanosecond.

(It's worth noting that this is not the speed of electrons moving through the wires, which is dramatically slower. The signal is a disturbance that propagates more rapidly than the drift velocity of electrons in a conductor.)

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So how is it that data transfer is so slow comparatively in copper? Why doesn't it transfer without a delay say between 2 computers. Could you expand on the second part of your answer which is in brackets? –  Jonathan. Nov 8 '10 at 1:16
The speed of light and the speed of data transfer has no relation. True, electrons flow slower in copper, but these phenomena are not related. –  Vortico Nov 8 '10 at 2:20
Please use SI units. –  ths1104 Nov 8 '10 at 3:19
@Jonathan: The delay in data transfer is a result of the circuits of your network card, and an increasing error rate with cable length that has to be corrected. For the bracketed part: Electrons in a typical conductor only move at some meters per second or slower (say, snail-electrons), but since the electromagnetic field caused by their acceleration/deceleration propagates with the speed of light, it causes the next electron to also accelerate/decelerate almost immediately. You can compare this to a line of magnets, when you push the first one the others will also move but they're all slow –  Tobias Kienzler Nov 8 '10 at 8:34
One example: if you have a decent copper coaxial cable, an electric signal would travel round the world 5 times in a second, or from London to New York in 28 Milliseconds. (This calculation uses the speed given in the link by TheMachineCharmer, here: en.wikipedia.org/wiki/Speed_of_electricity) –  thomastiger Nov 8 '10 at 10:11

NO. Electricity is NOT instantaneous.

Light has finite velocity 3 x 10^8 m/s.

Nothing can travel faster than light. Means everything has finite velocity less than light. Nothing travels instantaneously. Hence electrons have finite velocity too.

How fast does electricity travels? here
Why does it appears to travel so fast? here

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@mplungjan Good one! lol :D –  Pratik Deoghare Mar 29 '11 at 7:48

The speed of conduction of electricity (usually voltage) in a conducting wire is usually determined by the time it takes for the current to saturate the capacitance of the wire or circuit. For example, this is why local processes on the same computer chip run much faster than the same process offloaded to a separate chip, i.e. the circuits have much lower capacitance.

Note that this is completely distinct from the universal maximal propagation velocity of any causal interaction in the universe, as seen by any observer, which also happens to be the speed of electromagnetic propagation in a vacuum, also called "c".

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From the point of view of simple models, one can depict "little particles" called electrons - huge amounts of them - moving slightly through a lattice of atoms because of an external cause that created a force field in the material. The movement of the particles is a drift velocity really quite slow. E.g. in a cupper wire of 1 mm diameter and a current of 3 amperes, the drift velocity of electrons is approx. 1.0 m/hour (for the calculation see the numerical example).

The velocity of the electric signal through the wire is with the speed of light however. To get the idea, one can depict a tube filled with marbles. When you insert a marble at one end, "instantly" another marble falls out at the other end, however the marbles themselves only shift over a small distance.

This is an explanation from the point of view of a particular (simple) model. Things become more complicated, more difficult or impossible to depict in the context of other models, e.g. pure quantum mechanics. In a pure quantum mechanical model individual hard core electrons do not exist and the explanation becomes purely mathematical.

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I can understand that however I've also been told that electrons carry energy which is effectively the electricity. So if I put energy into a marble in one end of the tube then the marble that falls put the other end will not have any energy –  Jonathan. Nov 8 '10 at 14:21
In the model of the tube: You have to exert a force to push a marble in the tube, this force corresponds to the voltage. Then the marble moves - no áll the marbles in the tube move together! - so they all have kinetic energy, this corresponds to the energy electrons carry with them. When the marble drops out at the other end, it also has kinetic energy. –  Gerard Nov 8 '10 at 21:28