In power grids, how fast do individual electrons move?


My understanding is that current flow is like when you have a garden hose that is already full of water: as soon as you open the tap, water instantly comes out of the other end of the hose.

So when a generator pushes current through a power grid, do the electrons move at the speed of light (as many believe), or is it more a case of them all bumping each other along instantaneously,, as with the molecules of water in the garden hose?

In: Physics

> Water instantly comes out of the other end of the hose.

No, actually it’s not “instantly”, that’s the part that happens at the speed of light (for electrons).

As far as the electron movement, that’s called the [drift velocity]( of electrons in wire, and it depends on the material (what metal it is, dimensions, etc.), and on the electric field (voltage, etc.).

It is a great question. The analogy of water flowing in a pipe, sort of breaks down once you get to the level of electrons and such.

1) Electrons are not massless particles. Therefore electrons cannot travel at the speed of light. The explanation is from Einstein: that anything with mass would need infinite energy to accelerate to the speed of light.

2) What is “moving” at the speed of light is the change in the electromagnetic field. The term used is propagate rather than move.

3) The speed of individual electrons cannot actually be measured with precision. But the presence of a voltage in wire will induce a “general flow” of electrons in one direction. (Imagine water in a turbulent river – we cannot say what speed any particular drop of water is moving but we can tell how fast the entire flow is moving in general) This flow speed is called “drift velocity” and is called drift because in most circumstances it is VERY slow.

4) Drift velocity direction depends on which side of the wire has higher voltage relative to the other. In power grids, the voltage is AC, so it swings from positive to negative. In effect the drift velocity switches each time the voltage switches signs and therefore the average drift velocity in the power grid is ZERO. That is, electrons aren’t “shooting out” at one end of an electric cable.

So one can imagine electrons essentially moving backwards and forwards but not really going anywhere. This is just an illustration – electrons don’t organize themselves like balls of stuff and their actual motion isn’t like cars going down a road.

I like to think of it as being more like a tube filled with tennis balls. As has been said, there are a bunch of factors that go together to give you the drift velocity. But this is ELI5, so let’s give you a ballpark figure.

In an electric circuit, the electrons are moving *slowly*. For example, in an average 2mm wire with a current of about 1A, the electrons are moving at about 23μm/s. That’s 23 *micro*meters, or 0.000023m every second. To put that into perspective, it would take about 12 hours to travel 1m at that speed. Or, say there was a wire going straight up, and there was heavy rainfall. The water level could actually rise faster than the electrons in the wire.

Two different things here

The speed of electricity is not how fast electrons move, but instead how fast the electric field moves. It’s the electric field that actually does the work, and that moves at a bit under the speed of light. The electric field at your outlet is constantly changing so there’s usable electricity there instantly and you don’t have to wait for it to come from the power station

The actual electrons don’t move much. They bounce around off the atoms in the wire and drift in one direction slowly, very slowly

The average speed after all the bouncing around of 1Amp of current in a 3 mm^2 wire(roughly the size in your walls) is about 20 micrometers per second. Each electron is moving a fair bit quicker but with all the bouncing they can’t make much forward progress