Is voltage the speed of electrons?

Question

Current is the amount of electrons passing through a wire. Can we say that voltage is the speed of those electrons?

Voltage is more like pressure that drives the current. Speed is not the speed of the electrons (which move in mm/s) but the speed of the electric field (more like the speed of light). — Transistor, Jul 12 '16 at 10:37
The speed of electrons travelling *outside* a wire, such as in a particle accelerator, is often quoted in electron-volts for reasons I'll expand on. — pjc50, Jul 12 '16 at 11:06
electrons want to be evened out (more accurately is to say that they repel each other). if you pile a bunch of them up in one place, and have an absence of them near to it, they will really really "want" to move to the empty place. the bigger the difference between the presence of them in one spot, and the absence of them in the other, the more they will "want" to move. the "wanting to move" is the voltage (as others said, pressure). if this "wanting to move" gets strong enough, the charge can travel through something it would normally not be able to, like a lightning bolt through the air. — Dave Cousineau, Jul 12 '16 at 17:13
Current is not the amount of electrons passing through a wire. Instead it is the amount of charge passing through the wire per unit time. — nidhin, Jul 12 '16 at 18:26
You might be interested in [vacuum tubes](https://en.wikipedia.org/wiki/Vacuum_tube), most notably the [x-ray tube](https://en.wikipedia.org/wiki/X-ray_tube). The voltage between cathode and anode accelerates electrons to an energy of voltage*electron-charge. Also note that 1 A = 1 C/s while 1 V = 1 J/C, i.e. while current denotes charge per time (as you mentioned), voltage simply gives you the _energy_ that charge has. — Tobias Kienzler, Jul 13 '16 at 07:01
Voltage is the water in the water tower, how much and how high above where you are using it determines your potential energy. The water would be the electrons in this case. Once it starts flowing the flow of the water is the current like the electrical current of the flow of electrons. And you have resistance in the pipes and elsewhere in the system just like you would with electricity, and the combination of the energy of the water in the tower, the resistance and the resulting flow are like voltage current and resistance in electricity, you cant change one without affecting the others. — old_timer, Jul 13 '16 at 13:52
In high-energy physics, “speed” is often sloppily used as a synonym for kinetic energy (of course this isn't really right: energy increases quadratically with speed, and even more in the relativistic range), and the kinetic energy is measured in electron-volts. However, this is only applicable to free particles in a vacuum tube/tunnel – in a metallic conductor, the kinetic energy is pretty much completely negligible. — leftaroundabout, Jul 13 '16 at 15:13
Voltage is an 'effort variable' and current a 'flow variable'. — Karlo, Jul 14 '16 at 12:07
Astonishingly, no one cared for clarification about pressure. Voltage is like **gauge pressure** (difference in pressure). Electric potential would be an analog of barometric pressure had it some absolute reference point. — Incnis Mrsi, Aug 30 '16 at 09:21
It seems electrons don't actually travel that fast, what moves fast is the chain effect https://www.youtube.com/watch?v=jbi7gJTPSXk — MeTitus, Apr 19 '20 at 19:27
If that was the case, voltage would be measured in metres per second, not Volts. — Shashank V M, Jul 07 '20 at 10:53

score 37 · Accepted Answer · edited Mar 22 '23 at 19:24

37

Is voltage the speed of electrons?

No, it's not the speed of the electrons moving within the conductor.

The voltage unit is potential energy per charge:

An example...

Imagine we have a ball of mass M = 10 kg.

This ball exists in a conservative gravitational field (the Earth's gravitational field). If we want to raise it by a height of 1 meter, we must - somehow - supply an X amount of energy, that gives the ball enough speed to move 1m above the Earth's surface.

We will give the ball this amount of energy in terms of kinetic energy (speed). So we throw the ball upwards with some speed, and as the ball moves upward, its speed decreases; and its potential energy increases until it stops and all the kinetic energy is converted to potential energy.

The following picture shows the amount of potential energy for a ball of mass M = 10 kg at different heights above sea level:

But what if we want to make a generic scale?
For any ball of an arbitrary mass, at any height, we can get the amount of energy for every 1 kg in it (Energy per mass):

Now we can say that, at a height of 3 meters above sea level, any object of mass X will have an amount of energy equals 29.4 joules for every 1 kg of mass. This is due to the earth's gravitational field.

Voltage, or electric potential, is the amount of potential energy (joules) that any "charged body" within an electric field will have, for every 1 coulomb of electric charge in it.

edited Mar 22 '23 at 19:24

feetwet

2,322
9
31
55

answered Jul 12 '16 at 13:04

Elbehery

1,290
10
15

One might add that the potential energy *does* directly translate into kinetic energy if there is only negligible "friction", for example in an (evacuated) cathode ray tube. The kinetic energy of an electron is indeed measured in "electron volts", eV, the energy an electron gains or loses when moving through a potential difference of 1 Volt. – Peter - Reinstate Monica Jul 14 '16 at 11:24
It's not that isolated right? Since With V = I/R a V increase also forces a I increase. So the number of coulombs also increase by the same amount. – Cojones Dec 02 '18 at 06:40
1

Voltage is not the speed at which electrons move, but at the atomic level, what is it that makes a higher voltage deliver the same power as a lower voltage with higher current? Something must be happening to the electrons. 1 C of charge in a 100V circuit will 10x more power of 1 C of charge in a 10V circuit but what does that even mean? Does it mean that the electrons have more energy to push whatever comes in front of them? – MeTitus Apr 19 '20 at 18:59
@MeTitus Yes. Energy is charge times voltage. One electron accelerated through 100 V will gain 100 eV of energy. Or 10 electrons accelerated through 10 V will in total gain 100 eV of energy. In a resistor all of this energy the electrons gain will be lost to the resistor in the form of heat. – Matt Feb 04 '21 at 02:19
2

But the ball's speed increases if it is dropped from 3 meters, so does voltage affect the speed of electrons? – Qwerty Feb 27 '21 at 18:11

score 31 · Answer 2 · answered Jul 12 '16 at 11:18

31

Voltage is a property of an electric field.

An electric field behaves a little like a gravitational field. Objects in a gravitational field are pulled together. Drop a stone in a gravitational field and it will accelerate downwards, taking energy from the field.

Electric fields, unlike gravitational fields, have polarity. Drop an electron in an electric field and it will accelerate in the direction of positive charge. The electron does not have a voltage, it has a charge: \$1.6×10^{−19}\$ coulombs.

How much force is applied to the electron depends on the voltage of the positive and negative sides of the field and their distance apart.

That's all in free space. What about inside a wire? The situation there is much more like a tube filled with balls than a free space. Apply a force to the ball at one end and it will push the ball at the other end out. Apply a voltage to a wire and the electrons will move, forcing out the one at the positive end. The amount of force applied corresponds to the voltage applied to the wire.

The key thing about this model is that the force travels much faster than the balls/electrons that are transmitting it - it doesn't require a ball/electron to go all the way through, it just requires it to push its neighbours along.

answered Jul 12 '16 at 11:18

pjc50

46,540
4
64
126

This is a good analogy, but it is important to note that the electrons flow out of the negative side, not out of the positive side. – DerStrom8 Jul 12 '16 at 12:06
Sorry, inadequate labelling by me there: if you have a DC power source, the electrons will leave the wire connected at its positive side and enter the power source. – pjc50 Jul 12 '16 at 12:45
Voltage is not about the force (= energy/displacement). Voltage is about the *difference in energy potential*. That is field strength which, multiplied by charge, produces force. – Incnis Mrsi Aug 30 '16 at 09:24
"How much force is applied to the electron depends on the voltage of the positive and negative sides of the field and their distance apart." but how does that force affect the electron? How does lower/higher voltage affect the electron since the charge is a constant? Thanks – MeTitus Apr 19 '20 at 19:11
"Sorry, inadequate labelling by me there: if you have a DC power source, the electrons will leave the wire connected at its positive side and enter the power source." Are you saying that in a DC power source like a battery, the electrons flow from the positive to the negative side?! – MeTitus Apr 19 '20 at 19:15
@MeTitus *inside* a battery: yes, the positive terminal of a battery takes in electrons and the negative side of a battery emits electrons. They aren't usually carried all the way across the battery, what happens is the atoms inside the battery changing oxidation state by acquiring or giving up electrons. – pjc50 Apr 20 '20 at 09:16

score 5 · Answer 3 · answered Jul 12 '16 at 11:59

5

Take a Real time scenario,

We can take it water as analogy.

Lets consider a overhead tank and a water tap which is supplied from this over head tank.

Now,

Whenever open a tap water will come through this tap.

The amount of water which is coming through is equivalent to the current

At what Pressure is coming, that is voltage

answered Jul 12 '16 at 11:59

Photon001

824
6
17

10

The problem with this analogy is higher pressure imparts the water with greater velocity, which is likely why the asker's confused - this is one place where the popular analogy of water to electricity breaks down. It's a good, intuitive way to explore many aspects of electricity, as long as you don't look at it too carefully. – talrnu Jul 12 '16 at 20:39
Yes @talrnu, if we consider the velocity we will get confused. Its not exact electricity analogy, Just i took two phenomena of the water pressure and quantity to easily grasp the what is the voltage and current – Photon001 Jul 13 '16 at 05:24
1

Agree, this answer is problematic because the speed of the flowing water increases with pressure, while the speed at which an electron propagates through any particular medium is constant even if the "pressure" (voltage) is increased. I think what the OP is really asking is _why_ that's the case. – aroth Jul 13 '16 at 07:33
1

@talrnu I'm on that boot too. Since higher voltage delivers the same power as lower voltage with higher current, then something must be happening at the atom level that allows the lower current to deliver the same power despite the lower voltage. The charge per electron is sorts of a constant so what is changing? Thanks – MeTitus Apr 19 '20 at 19:20
1

@aroth If all the variables are constants as it seems, what changes to the electrons when applying a higher lower voltage? The velocity at which the electrons move, the drift velocity seems to be quite low as well, so what changes: https://www.youtube.com/watch?v=jbi7gJTPSXk – MeTitus Apr 19 '20 at 19:31
If I understand the accepted answer correctly, the amount of useful energy per charge carrier is what changes. Though that's still kind of vague. But 'drift velocity' seems misleading. Obviously there are charge carriers moving well in advance of the electron depicted in the video, else the light wouldn't illuminate. So I guess if you consider the motion of a single charge carrier in a fixed-current application then its velocity is constant and what changes as voltage increases is the amount of energy is carries. Which, if velocity is constant, must be its mass, as expressed in eV? – aroth Apr 20 '20 at 03:31

score 4 · Answer 4 · answered Jul 12 '16 at 10:55

No, the voltage is the "potential energy" given to electrons. Like as if you take a stone and lift up. Until you do not connect a load the electron don't go anywhere.

If you let it falling down the stone (or connect a resistor at your voltage source) the energy move the stone (electrons).

score 3 · Answer 5 · edited Jan 20 '19 at 17:14

Is voltage the speed of electrons?

No

Voltage is a measure of how much energy is delivered to charge. At its most basic, an electron (basic charge) is imparted 1.602×10⁻¹⁹ joules when moved through an electric potential difference of one volt. An electron is then said to have an energy of 1 electronvolt.

So voltage is energy divided by charge.

You can start with power and multiply it by time to get energy:

Energy = Power × time = V⋅I × time.

Now substitute Q (charge) for current × time and you get:

Energy = V⋅Q or V = Energy/Q.

Ben Miller - Remember Monica · Answer 6 · 2016-07-12T20:24:12.300

3

No, voltage is not the speed of electrons through a wire, but current (almost) is.

You said, "Current is the amount of electrons passing through a wire," but this is not quite correct. Current is the amount of electric charge (electrons) passing through a conductor per unit of time. The ampere, our unit of measure for current, is defined as 1 coulomb of electric charge per second. Current is a rate value.

For the water pipe analogy, charge (coulombs) is analogous to the volume of water (gallons), current (amps) is analogous to flow rate of water (gallons per minute), and voltage is analogous to the water pressure that is causing the flow.

edited Jul 12 '16 at 20:24

answered Jul 12 '16 at 18:10

Ben Miller - Remember Monica

626
4
13

2

Current is not the speed of electrons through a wire, it's the *rate* at which they flow past. If the channel is wider, they will flow slower to produce the same current. – endolith Jul 12 '16 at 20:10
@endolith Speed, rate, close enough. :) I changed the wording slightly. Better? The point is that current is that change over time that I believe the OP is asking about. – Ben Miller - Remember Monica Jul 12 '16 at 20:26
Yes, better. :) – endolith Jul 12 '16 at 21:12
Voltage is never almost the speed because the speed of electricity is constant. Voltage is the potential and current is the amount. The speed is constant. – John Peters Jul 13 '16 at 10:31
1

@JohnPeters I think it is a little too simplistic to say that current is "the amount" of electricity. Current is the amount of electrical charge that passes a point in a unit of time. In that sense, it is the rate (or speed, if you like) of charge. – Ben Miller - Remember Monica Jul 13 '16 at 13:26
1

@JohnPeters What is the speed of electricity? is it the speed of electrons in the conductor or the speed of voltage change? – Crowley Jul 13 '16 at 16:13
@JohnPeters The speed of electricity is not constant. If by "speed" you mean electron drift, it depends on the current and width of the wire. If instead you mean the wave propagation speed, it depends on the dielectric constant of the cable. https://en.wikipedia.org/wiki/Speed_of_electricity – endolith Jul 13 '16 at 16:37

score 2 · Answer 7 · answered Jul 12 '16 at 11:23

2

This is actually a physics question. I don't believe there is an experimental method available in the confines of the electrical engineering discipline to answer this question credibly.

Having said that, it is commonly believed that the speed of electrons in a conductor experiencing current flow is actually quite slow compared to the speed of light. This is often referred to as the "drift speed" of the electrons. However, the effects of voltage and current on the electrons is propagated thru the conductor at nearly the speed of light. The usual analogy is a pipe filled with marbles. If you push the marble at one end of the pipe the marble at the other end will experience the push nearly instantaneously even though none of the intermediate marbles moved.

answered Jul 12 '16 at 11:23

FiddyOhm

2,684
13
13

2

Not sure if "nearly the speed of light" is the right expression - it's around half that in an ordinary PCB and 2/3 in common coax. – pipe Jul 12 '16 at 11:51
@pipe I think the difference is that a single electron may travel at, say, half the speed of light, but considering the ball in a tube analogy, the response time between pushing in the first ball and the last ball falling out is nearly instantaneous (approaching the speed of light). – DerStrom8 Jul 12 '16 at 12:10
2

@DerStrom8 No, the response time is the signal velocity here, which is slowed down by the dielectric in the PCB and the cables. It only approaches speed of light in a bare wire. A single electron travels much much slower than half the speed of light. – pipe Jul 12 '16 at 12:15
Hmm, I'm not convinced but I won't argue it. Physics class was a long time ago =P – DerStrom8 Jul 12 '16 at 12:17
The drift velocity of electrons in a wire under normal electronics conditions is positively glacial. A 1mm^2 cross-section wire carrying 10A has a drift velocity of only about 1mm/second! This is effectively a slight bias in the thermal velocity of the electrons which are zooming around at 10^6 m/s or so at room temperature. That's still slow compared to the speed of light (~3E8 m/s) – Spehro Pefhany Jul 13 '16 at 15:57
@Spehro Pefhany: *Thousand kilometres per second* at room temperature? It would result in *v²/c²* about 1/89876 and kinetic energy about 2.85 eV (electron’s rest mass is 511 keV */c²*). You clearly exaggerate. – Incnis Mrsi Aug 30 '16 at 10:59
1

@IncnisMrsi Indeed, calculating it I get more like 1.08E5 m/s at 300K. – Spehro Pefhany Aug 30 '16 at 11:42

score 2 · Answer 8 · answered Jul 12 '16 at 11:49

2

Voltage is the pressure that pushes electrons around a circuit. It says nothing about their speed. If you take a 1.5V battery and don't connect it to anything, then there's still 1.5V present, even though no electrons are flowing anywhere.

Further, voltage is the pressure difference between two points. You can only measure the voltage between one point and another. That's why it's also called "potential difference".

It is possible to calculate the average electron speed if you know the current, the physical properties of the wire (particularly its cross-sectional area) and the properties of the material the wire is made from (the spacing between the atoms, and how many free electrons there are per atom).

answered Jul 12 '16 at 11:49

Simon B

18,609
1
29
55

I'll not talk about pressure. It's a really different concept, IMHO. – Antonio Jul 12 '16 at 12:07
2

@Antonio Pressure and voltage are very similar concepts, if not identical. – endolith Jul 12 '16 at 20:10
@endolith, now my professor of physics may be turning in his grave. :-) – Antonio Jul 12 '16 at 23:31
1

@Antonio Attach a dynamo and generate some voltage :D – endolith Jul 13 '16 at 01:51
@endolith, Ah! Ah! :-) Now I understood.... :-) – Antonio Jul 13 '16 at 09:37
1

@endolith I always use the water flow and pressure as analogy for current and voltage. KCL and KVL works perfectly well. – winny Jul 13 '16 at 13:43
Excellent. Don’t waste your time answering at physics.SE, guy – you are too good for it ☺ – Incnis Mrsi Aug 30 '16 at 09:38

score 2 · Answer 9 · answered Jul 12 '16 at 17:00

2

If an electron was a marble, Voltage is like the height of the slope that the marble is at the top of.

It might be a really tall slope - miles high. It might be a tiny rise - just a couple of centimetres. That's what's determined by the voltage.

answered Jul 12 '16 at 17:00

Euan M

131
3

1

I feel like this analogy could be expanded into a great alternative for other related concepts too. If voltage is the height, what's the angle of the hill correspond to? Maybe resistance could be represented by grass or mud. Then you've got the number of marbles, the horizontal distance from hilltop to base (which is going to relate with height and angle just as the corresponding electrical concepts do)... – Dan Henderson Jul 13 '16 at 22:17
I agree, but I'm on lousy internet atm. :-) – Euan M Jul 13 '16 at 23:32
Speaking of the height, they are using this effect to heat and cool the atoms by bouncing electrons at different heights https://www.youtube.com/watch?v=O6waiEeXDGo Does that relate? – Qwerty Jun 25 '21 at 23:57

score 1 · Answer 10 · answered Jul 12 '16 at 10:56

Voltage isn't a property of electrons. Electron are the 'subjects' as it is. A voltage (or potential difference) is the 'ability' to transport a certain charge. In electronics, this charge is generally carried by electrons. A higher voltage is able to carry more electrons, hence induce a higher current.
Another way of looking at it is that the voltage is the amount of potential energy that an electron gains or looses by traveling from one potential to another potential. In this way, voltage is very similar to potential energy in kinetics - if I lift a ball, the ball's properties doesn't change but it gains potential energy.

A good start, but slipped deeply into crap very soon. Ever heard of superconductors? Voltage has nothing to do with “ability to transport”. Voltage is, rather, energy output for a unit of charge transported. — Incnis Mrsi, Aug 30 '16 at 09:30

score 1 · Answer 11 · answered Jul 14 '16 at 11:52

The speed of electrons depends on the density of the wire. It also depends on the number of free atoms in the conductor.

Think of it like pushing sand through stones. The more dense the stones are, the harder it becomes pushing the sand through it.

The more sand (free electrons) is inside, the less distance you'll need to push for the same amount of sand dropping out at the other end.

For details, you may read about drift velocity. The actual speed of an electron in the example there is just as little as 23µm/s.

In fact, the voltage will influence the speed of electrons: in the given formula, replace I by U/R and you'll see that the velocity will increase with the voltage.

Tony GR · Answer 12 · 2019-07-02T08:18:35.613

A lot of good information here to hopefully clarify your question.

The voltage can be thought of as the energy difference between two points within a network (potential difference), think about the voltage dropped across a resistor. Different at each end due to the power dissipated across the resistor itself.

If your where to consider the supply voltage to a circuit (EMF, electromotive force), it can be thought of as the pressure forcing current through the circuit.

a note about electron flow

The convention is taken to be that current moves from + to -, this however electron flow is - to +. The formulas etc of course will work with this convention, as usually we dont care about electron flow, unless we are into semiconductor stuff, however its important to remember they actually flow from - to + (the electron being a negitive charge carrier).

I hope this along with the many other comments helps. Tony

Electron does neither necessarily nor usually “move from + to −”. It *gains energy* moving from − to +. — Incnis Mrsi, Aug 30 '16 at 09:42
@Tony. "*The convention is taken to be that electroncs move from + to -, ...*" No, the convention is that **current** flows from + to -. In conventional circuit theory we don't care what the actual charge carriers are or the direction of their movement. — Transistor, Jan 20 '19 at 18:45

score 0 · Answer 13 · answered Jul 02 '19 at 08:27

No. The simplest answer possible is that voltage is the density of electrons. That is, the "pressure" required to push them together against their repulsive force. Of course, this is complicated by other factors such as the medium in which they are moving.

Is voltage the speed of electrons?

13 Answers13

Linked

Related