does the speed of an electron going through a wire depend on the voltage? intuitively I would think that the speed of an average electron would be faster with higher voltage than one at lower voltage. I am aware that the ‘speed of electricity’ as commonly understood is very fast…I’m asking about the average speed of an electron in a wire at different voltage potentials.
Electricity in a wire is kind of a funny thing.
Think of it more like this. Take a hollow hula hoop and cut it open, then fill it with marbles. Then shove an extra marble in one end. A marble pops out the other end, but it’s not the same marble that you shoved into the first end. The movement of electrons is kinda like that. The “electricity” moves a lot more than the actual electrons.
The actual movement of the electrons depends on the amount of current flowing and the cross-sectional area and the geometry of the electrical conductor. All other things being equal, a greater voltage makes a greater amount of current flow, but it’s entirely possible to have more current flow with a lower voltage if all other things aren’t equal. So the dependency is more on the current than on the voltage, but the current and voltage aren’t completely unrelated.
In alternating current there is no net flow of electrons; they just bounce back and forth like small children in an inflatable castle. In direct current, the flow rate of electrons is determined by the permittivity of the conductor and the potential of the electric field. For a given current the averaged electron flow rate should be proportional to the voltage (which represents potential) but from a power supply an increase in voltage is generally accompanied by a change in the current. It should also be noted that all of this assumes a steady-state condition with no external or self-induced magnetic response (i.e. induction); all real world electric conductors are subject to some degree of self-induced magnetic field interaction even in a perfect vacuum.
The actual movement speed of electrons even in high voltage direct current transmission is very slow, on the order of 10[SUP]-3[/SUP] meters per hour. The transmission of actual energy is the result of exchanges of virtual electrons between atoms a metallic lattice. That electrons form a sort of interstitial fluid (in a conceptual sense) in conductive metals and some other materials rather than being more fixedly bound in the case of ionic and covalent bonded materials gives them this high transmissibility. This is what also gives pure metals their characteristic luster.
Stranger
Note that this is the net movement speed. The electrons are actually moving quite fast, but they jiggle backward almost as often as they jiggle forwards, so their net flow is very little.
Not in direct current applications, which Stranger was talking about.
The short answer is yes.
What you are talking about is drift velocity, which as Stranger said is typically very slow. The drift velocity is proportional to the electric field, and hence in the case of a typical conductor, proportional to the applied voltage.
This is true whether talking about AC or DC; it’s just that with AC, the drift velocity, current, and voltage change over time.
Line transmission effects (as you would have with very high frequency signals) break the usual relationship between electric field and voltage, but these effects are minor for typical power transmission cases.
Imagine a really long, rigid stick. A bar or rod of metal, say. Then imagine that we set it up in such a way as to connect my house to yours, with the bar hanging on a rope or something so that it can still move. I can push my end of the rod and, at the speed of sound (in that rod, which will be faster than the speed of sound in the air), the rod will move on your end too.
We can use that as a method of communication or of transmitting power (the bar could ring a bell, or push a lever). But the atoms on my end of the bar didn’t move very fast, or very far. We could set it up so that I can push the bar in one direction to ring the bell, or just vibrate it back and forth. In the latter case, the atoms in the bar wouldn’t really go anywhere except move back and forth slightly. But energy is still transmitted.
In general, the speed of the atoms in the bar isn’t really relevant to the speed of energy transmission. It depends on the method I use (vibrate – AC, or push – DC), how much force I use, the specific makeup of the rod, and what I’m pushing (the load) on the other end. But the energy always goes the speed of sound (or in the case of electric current, the speed of light for that transmission line). It’s not a perfect analogy, but I find it helpful.
What will really bake your noodle is that even though the electrons are moving only a fraction of a millimeter per second, this is a relativistic speed as far as electromagnetism is concerned.
The magnetic field you get from a current in a wire is (by one way of looking at it) a result of length contraction from the moving electrons. This creates a difference in effective charge density and hence an electronic force.
The electrons are slow and hence the correction is tiny–something like one part in a trillion. But the electromagnetic force is tremendous, and a tiny imbalance leads to macroscopic forces.
Even in direct current applications. The only difference that in DC, electrons jiggle forward almost as much as the jiggle backwards (resulting in a net flow), while in AC electrons jiggle forward excatly as much as the jiggle backwards (resulting in no net flow).
Or to put in another way, in the absence of an electric field, the electrons are moving about quite quickly just thermally. All the electric field does is put a trend on that motion.
Which makes you wonder: can’t we just put a really fast diode on a loop of wire, and generate a net current from all this thermal motion?
The answer is no, but the reasons aren’t as obvious as one might think. Basically, you can’t build a diode that good–for whatever thermal motions we get at some temperature, the diode will leak in a way such that we get no useful work out of it.
It’s basically the electronic equivalent of Feynman’s ratchet, which posits extracting energy from a thermal bath via a mechanical ratchet. They’re both forms of a Maxwell’s Demon, and don’t work, but for fairly subtle reasons.