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Electricity Doesn't Flow Through Wire

I remember studying electrical engineering at an introductory level way back in the '90s and the tutor said back then that electricity doesn't flow positive to negative as most people assume. He also said electricity is extremely weird in how it works and that what we know about it isn't completely accurate and nor is what we know definitive. The takeaway learning from that course is that electricity is weird!
 
If I understand correctly, he is saying the speed at which the lightbulb lights is faster than the speed of light in the cable? That cannot be correct. In that case we have a simple signalling system that operates at faster than the speed of light?
 
venton said:
If I understand correctly, he is saying the speed at which the lightbulb lights is faster than the speed of light in the cable? That cannot be correct. In that case we have a simple signalling system that operates at faster than the speed of light?
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No, he is saying that the energy moves through the space around the cable. Obviously close to the cable it's stronger, but since there is a 1m gap between the switch and the bulb, the first power reaches the bulb when the field from the battery reaches the bulb, and as they are 1m apart, it takes 1/c seconds (where c is the speed of light). So the energy flows at the speed of light to the bulb. He did however qualify this by saying that not all the power went this route, so it would be measurable, but low in power.

Science is about modelling the world, and the models are proved by how well they predict results. The experiment he is proposing manages to demonstrate a weakness in one model, but that doesn't mean the model is not useful, it just finds it's predictive limit. He doesn't go on to show that the new model he is proposing isn't itself broken in other situations, or for that matter, in one that the other model succeeds.

There is then a serious problem of conflation between the physical world and the model which seems to occur in almost all popular science discussions (and scientists themselves forget this and get caught by it all the time). Much confusion comes from thinking that models are 'right' or 'wrong' when they are all just tools to make predictions, so if you want to go on thinking of electrons flowing down cables and passing on power, then that's fine, in the same way that newtons theory of gravity works well, F=ma for example, even though we know from general relativity that this doesn't predict measurable effects we see.
 
windhoek said:
I remember studying electrical engineering at an introductory level way back in the '90s and the tutor said back then that electricity doesn't flow positive to negative as most people assume. He also said electricity is extremely weird in how it works and that what we know about it isn't completely accurate and nor is what we know definitive. The takeaway learning from that course is that electricity is weird!
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The other take-away is that depending on the level at which you learn your physics the (probably universal) practice is that when you get taught certain things, what you are taught can range from "incomplete" to "inaccurate".

I twigged this as an A-level physics student when a fellow student asked a detailed question of a physics teacher who was not teaching the A-level course, and that teacher had to enquire first about what he had been taught at a high level before answering the detailed question.

My conclusion was confirmed - in the exact same topic - when I was an undergraduate reading solid-state physics and seeing how incomplete the A-level coverage had been.
 
Cesare said:
...Science is about modelling the world, and the models are proved by how well they predict results. The experiment he is proposing manages to demonstrate a weakness in one model, but that doesn't mean the model is not useful, it just finds it's predictive limit. He doesn't go on to show that the new model he is proposing isn't itself broken in other situations, or for that matter, in one that the other model succeeds. ...
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Exactly right. We have models of the real world that work well in the right circumstances but they should not be confused with the real world itself.

In this particular case I have a professional paper in my files which mathematically shows that calculating load power dissipation from consideration of electron movement produces the same result as calculation from the E-M field. (I admit I haven't read it - I filed it when I found it, for later reading, and I haven't got around to it :().
 
ks.234 said:
I’ve only just learned that everything I was taught about where money comes from is a lie, now everything I thought I knew about electricity is a lie too.

I need a lie down
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My understanding of electricity is so vestigial that this revelation is not shocking at all.
 
I am increasingly of the opinion that Lou Reed was right in asserting that ‘electricity comes from other planets’.
 
John Phillips said:
The other take-away is that depending on the level at which you learn your physics the (probably universal) practice is that when you get taught certain things, what you are taught can range from "incomplete" to "inaccurate".

I twigged this as an A-level physics student when a fellow student asked a detailed question of a physics teacher who was not teaching the A-level course, and that teacher had to enquire first about what he had been taught at a high level before answering the detailed question.

My conclusion was confirmed - in the exact same topic - when I was an undergraduate reading solid-state physics and seeing how incomplete the A-level coverage had been.
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When I was studying A levels the Physics guy was very straight about this. It's a model, it works most of the time. Same goes for chemistry and electron orbitals. They're not really confined to an orbital, there's a cloud and it's all about probability. But it lets you understand why chemical elements behave as they do.
 
Wise enough to step it down though,



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stevec67 said:
When I was studying A levels the Physics guy was very straight about this. It's a model, it works most of the time. Same goes for chemistry and electron orbitals. They're not really confined to an orbital, there's a cloud and it's all about probability. But it lets you understand why chemical elements behave as they do.
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Well it sounds like you have enlightened teachers. I think that studying the history of science should be compulsory for all scientists, as you go from thinking that our forebears were cretinous fools for believing that there are four elements (earth, air, fire, water), there's an aether, or that the world is flat etc etc, to realising you're on a continuum, and that future generations will have the same low opinion about us and our current theories and understanding. 'They used to believe that electricity travelled in what they called electromagnetic fields in the space around the wire, ha ha ha' etc
 
Cesare said:
No, he is saying that the energy moves through the space around the cable. Obviously close to the cable it's stronger, but since there is a 1m gap between the switch and the bulb, the first power reaches the bulb when the field from the battery reaches the bulb, and as they are 1m apart, it takes 1/c seconds (where c is the speed of light). So the energy flows at the speed of light to the bulb. He did however qualify this by saying that not all the power went this route, so it would be measurable, but low in power.
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Not sure what the last 'qualify' might mean. But yes, the cables act as a 'guide' for an EM wave that is almost all entirely *outside* the metal. The speed then tends to be set by the EM properties of whatever surrounds the metal wires.

Many years ago in lectures on EM I used to switch on a light and then ask the undergrads: How does the generating station a 100 km away know I just operated that switch and 'instantly' provided more current to light the light? 8-]
 
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