How fast do electrons 'flow' through wire?
Discussion
I did pretty well at physics in most areas, although the area where I did struggle to some extent was electronics.
One question that held me back a bit whereby I couldn't get fully on top of it was a fundamental issue of how fast do electrons flow through a wire.
For example if one was to turn on a light bulb, the filament is 'instantly' filled with electrons which heat up the filament and produce light.
But also at the same time its said that an electron entering the wire from the 'source' would only trickle along the wire's length. Some say at the speed that 'honey would smoothly drop from a spoon'.
So from an individual electron perspective what is really happening?
One question that held me back a bit whereby I couldn't get fully on top of it was a fundamental issue of how fast do electrons flow through a wire.
For example if one was to turn on a light bulb, the filament is 'instantly' filled with electrons which heat up the filament and produce light.
But also at the same time its said that an electron entering the wire from the 'source' would only trickle along the wire's length. Some say at the speed that 'honey would smoothly drop from a spoon'.
So from an individual electron perspective what is really happening?
From memory of a degree in a previous life.
Wave propagation speed in copper is pretty much speed of light. It's wave propagation that transfers the energy.
Electron drift (that's watching an individual electron move down the wire) is glacial with DC and zero with AC; I recall mm per hour for DC but I may be wrong...
Wave propagation speed in copper is pretty much speed of light. It's wave propagation that transfers the energy.
Electron drift (that's watching an individual electron move down the wire) is glacial with DC and zero with AC; I recall mm per hour for DC but I may be wrong...
The electron flow is reckoned to be around walking pace, but they pass the charge on (which is electricity) at around 2/3rds the speed of light.
Don't take that as gospel mind you, as you'll have noticed, there are several variations of the answer which have popped up already, although it's fairly well established that electrons don't flow particularly quickly.
Don't take that as gospel mind you, as you'll have noticed, there are several variations of the answer which have popped up already, although it's fairly well established that electrons don't flow particularly quickly.
Surely it depends on the voltage and resistance?
I was looking at this recently albeit slightly differently – trying to understand AC running through power cables. For example, how can power ‘get’ anywhere if the current is constantly changing direction. However, after learning that electricity can flow in one direction for hundreds of miles in 1/50th of a second (based on 50hz AC) then that kinda helped me understand it a little more.
But yeah, in a vacuum, electricity can travel at something like 200,000km/sec but it’s notably less in a cable due to resistance and the fact that you’d need more current to be able to create the power to supply the country.
Very interesting subject.
I was looking at this recently albeit slightly differently – trying to understand AC running through power cables. For example, how can power ‘get’ anywhere if the current is constantly changing direction. However, after learning that electricity can flow in one direction for hundreds of miles in 1/50th of a second (based on 50hz AC) then that kinda helped me understand it a little more.
But yeah, in a vacuum, electricity can travel at something like 200,000km/sec but it’s notably less in a cable due to resistance and the fact that you’d need more current to be able to create the power to supply the country.
Very interesting subject.
mu0n said:
I was looking at this recently albeit slightly differently – trying to understand AC running through power cables. For example, how can power ‘get’ anywhere if the current is constantly changing direction. However, after learning that electricity can flow in one direction for hundreds of miles in 1/50th of a second (based on 50hz AC) then that kinda helped me understand it a little more.
The wave moves. The electron does not. With AC, drift velocity is zero.Think about ripples through water in a tank or a large sheet being shaken up and down, a wavefront can transfer energy but the molecules don't move "down the wire".
Mr E said:
The wave moves. The electron does not. With AC, drift velocity is zero.
Think about ripples through water in a tank or a large sheet being shaken up and down, a wavefront can transfer energy but the molecules don't move "down the wire".
Yeah I kind of understand that - like electrons bumping into each other to pass on the energy?Think about ripples through water in a tank or a large sheet being shaken up and down, a wavefront can transfer energy but the molecules don't move "down the wire".
But with AC, do they keep passing on the energy even though it reverses? If you could slow down time and see the energy being transferred, what would it look like?
So getting to the root of the issue; the electrons themselves are not the ones that enter the light bulb filament, rather it is the charge that enters the filament electrons that are already present within the filament material?
This means that the electrons given a charge at the source (ie. the turning on of the light bulb switch) pass on this charge at the beginning of the wire at very high speed meaning that along the 'wave' of this progressive charge the electrons have a charge of -2 (or more)? (rather than their stable state of -1)?
I do remember from my school days that teachers were trying to state to me that electricity (this at the time supposedly meaning the progression of electron movements) travelled at, or near, the speed of light.
But then electrons can not travel at the speed of light can they? As they have a mass.
This means that the electrons given a charge at the source (ie. the turning on of the light bulb switch) pass on this charge at the beginning of the wire at very high speed meaning that along the 'wave' of this progressive charge the electrons have a charge of -2 (or more)? (rather than their stable state of -1)?
I do remember from my school days that teachers were trying to state to me that electricity (this at the time supposedly meaning the progression of electron movements) travelled at, or near, the speed of light.
But then electrons can not travel at the speed of light can they? As they have a mass.
Mr E said:
Imagine a rubber sheet with rocks of different sizes on it....
....hang on...
You know what I mean though, The electrons don't flow that fast, they just 'excite' each other rather quickly.....hang on...
If the tube was stuffed full of snooker balls, no matter how slow or fast you pushed them, the end ball will most pretty much instantaneously when the first ball was pushed/excited.
Ross1988 said:
Mr E said:
Imagine a rubber sheet with rocks of different sizes on it....
....hang on...
You know what I mean though, The electrons don't flow that fast, they just 'excite' each other rather quickly.....hang on...
If the tube was stuffed full of snooker balls, no matter how slow or fast you pushed them, the end ball will most pretty much instantaneously when the first ball was pushed/excited.
AJI said:
So getting to the root of the issue; the electrons themselves are not the ones that enter the light bulb filament, rather it is the charge that enters the filament electrons that are already present within the filament material?
This means that the electrons given a charge at the source (ie. the turning on of the light bulb switch) pass on this charge at the beginning of the wire at very high speed meaning that along the 'wave' of this progressive charge the electrons have a charge of -2 (or more)? (rather than their stable state of -1)?
I do remember from my school days that teachers were trying to state to me that electricity (this at the time supposedly meaning the progression of electron movements) travelled at, or near, the speed of light.
But then electrons can not travel at the speed of light can they? As they have a mass.
Don't forget though that what's taught at school is initially quite basic, then as you advance through the education system, they tell you more and more detail, some of which will contradict the early stuff you learnt. This means that the electrons given a charge at the source (ie. the turning on of the light bulb switch) pass on this charge at the beginning of the wire at very high speed meaning that along the 'wave' of this progressive charge the electrons have a charge of -2 (or more)? (rather than their stable state of -1)?
I do remember from my school days that teachers were trying to state to me that electricity (this at the time supposedly meaning the progression of electron movements) travelled at, or near, the speed of light.
But then electrons can not travel at the speed of light can they? As they have a mass.
Super Slo Mo said:
Don't forget though that what's taught at school is initially quite basic, then as you advance through the education system, they tell you more and more detail, some of which will contradict the early stuff you learnt.
Ah, lies to children.I left university sure I actually knew less things than when I started.
Mr E said:
I understand your intent. I'm just lightly amused that 50% of physics questions usually wind up at the "imagine a rubber sheet" state.
Very true! Soon it may well be 'Imagine a graphene sheet'...ETA: Graphene instead of Graphite
Edited by Ross1988 on Tuesday 6th August 12:02
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