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An interesting explanation of how electrical energy works


Stereophilus
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This was posted already somewhere here.

 

Edit: hmm...nothing to debate, is how I understood it anyway.

 

Explained well though.

 

Here it is

Richard Feynman explained it pretty much this way, and he's been dead over 30 years.

Edited by muon*
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1 hour ago, muon* said:

This was posted already somewhere here.

 

Edit: hmm...nothing to debate, is how I understood it anyway.

 

Explained well though.

 

Here it is

Richard Feynman explained it pretty much this way, and he's been dead over 30 years.

Ah, ok. I missed that other post.

 

I think it’s worth noting electrons do flow through wire.  It’s more a question of how the “energy” is transferred as I read it.

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“The principle that electrical energy does not flow in the wires themselves but in the fields surrounding the wires (as given by the Poynting vector) is indeed correct. Electrical energy is not transported by electrons, it is transported by fields. M. That much of his presentation is correct and informative.”

 

 

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49 minutes ago, Stereophilus said:

Ah, ok. I missed that other post.

 

I think it’s worth noting electrons do flow through wire.  It’s more a question of how the “energy” is transferred as I read it.

Yeah It's the EMF as Andythiing says above and the vid explains.

 

Richard Feynman explained it as so much many decades ago, and that if you had to wait for the electrons to travel from the light switch to the light bulb for it to illuminate, you would be able to make a cup of coffee while waiting for it

 

So electrons move through a conductor very very....very slowly.

 

 

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50 minutes ago, Andythiing said:

“The principle that electrical energy does not flow in the wires themselves but in the fields surrounding the wires (as given by the Poynting vector) is indeed correct. Electrical energy is not transported by electrons, it is transported by fields. M. That much of his presentation is correct and informative.”

 

 

Were there things that he represented that were incorrect?

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As I understood the guy in the vid he does suggest that as alternating current ......well....alternates!  the electrons don't flow through the conductor, I would suggest this is not quite accurate, and it wouldn't apply to DC either.

 

But either way the energy is carried by the EMF that is created by the charge, but often folk talk about electrons traveling through a conductor near light speed, which is incorrect....they can move through a vacuum near to the speed of light but they move through a conductor at a snails pace.

 

Edit: as I understand it :$

Edited by muon*
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This recent video by Derek Muller (aka Veritasium) has already  received over 50,000 comments on YouTube, many of which have been critical. I usually very much like Veritasium's videos but I think this one is not up to his usual high standard, and leaves a lot to be desired. I would welcome an updated version of it. The current version arguably creates as much confusion as it attempts to put to rest!

 

I don't see much point in discussing on this forum how the video was presented, as there is potentially a huge amount of technical detail in  how the assumptions and explanations might have been worded more clearly.  We may find a number of YouTube videos presented in reply.  One such video was done within the first 24 hours!

I don't believe there is any implication in this video that would lead to a redesign of audio gear. It's more just how you might think about electricity current "flow".

Edited by MLXXX
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I enjoyed the video. and kudos to them.   It's always problematic trying to explain sophisticated scientific to lay-people.  You have to simplify it down to level that conveys meaning while not distorting the actual theory too much.

I remember back in Year 10 science how they explained the structure of the atom as electrons arranged in shells around the nucleus, like an egg.  And then a few years later in uni they say "well....... it's not that simple".  And that more sophisticated model was still nowhere near the understanding of atomic structure that the post-docs had, but as students we learnt.  Well, I didn't, not from university Chemistry.

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10 hours ago, muon* said:

But either way the energy is carried by the EMF that is created by the charge, but often folk talk about electrons traveling through a conductor near light speed, which is incorrect....they can move through a vacuum near to the speed of light but they move through a conductor at a snails pace.

 

Electrons has mass - so even in a vacuum it is hard for them to travel near to the speed of light. 

 

 

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3 hours ago, RoHo said:

I enjoyed the video. and kudos to them.   It's always problematic trying to explain sophisticated scientific to lay-people.  You have to simplify it down to level that conveys meaning while not distorting the actual theory too much.

I remember back in Year 10 science how they explained the structure of the atom as electrons arranged in shells around the nucleus, like an egg.  And then a few years later in uni they say "well....... it's not that simple".  And that more sophisticated model was still nowhere near the understanding of atomic structure that the post-docs had, but as students we learnt.  Well, I didn't, not from university Chemistry.

 

Yes, that hierarchy of explanations is how it usually works. It does make sense if one understands that Science is about developing models of the real world, and the adage that 'all models are wrong, but some are useful'. There is nothing wrong with a model that may lack the correct details, provided it usefully describe key concepts and ideas to the intended audience. Where it can go wrong is when people extrapolate or extend the model beyond its domain of validity. 

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17 minutes ago, LHC said:

 

Electrons has mass - so even in a vacuum it is hard for them to travel near to the speed of light. 

 

 

Yes they do.

Near is subjective, so how near is near?

 

Edit: also I said they "can", and that means under the right conditions, and near can be 'approaching'.

 

I hate explaining things when it should not be needed.

Edited by muon*
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A huge amount of energy is needed to accelerate an electron to close to the speed of light.  I think these two paragraphs provide a helpful perspective:-

 

How fast do electrons move?

 

As fast as you can get them going! Well not quite. One of the facts of life discovered in the 20th century is that the speed of light (300,000 kilometers per second) is the ultimate speed limit. As you add energy to the electron, it will go faster, but as you get it to go close to the speed of light, you find that you have to add even more energy just to bump it a bit faster. For example, with just over 220,000 eV (which stands for a convenient unit of energy called the "electron-volt"), you can get the electron up to 90% of the speed of light. But to get it to 99.9% (just another 9.9 percentage points), you need a total of over 11 million eV! One way of looking at this is that the electron gets "heavier" (more massive) as it goes ever faster. So it's harder to push it faster. At Jefferson Lab, a typical energy for the electrons in the beam is 4 GeV which is 4 billion eV. That means the electron is traveling at 99.9999992% of the speed of light. Close but still not 100%.

 

You may wonder how fast the electrons are whizzing around in the atoms around you. A good example (and the most simple to calculate) is the hydrogen atom which is in all our water. A calculation shows that the electron is traveling at about 2,200 kilometers per second. That's less than 1% of the speed of light, but it's fast enough to get it around the Earth in just over 18 seconds. Read up on what happens when nothing can go faster than the speed of light.

 

Author:

Carl Zorn, Detector Scientist

Edited by MLXXX
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10 hours ago, MLXXX said:

It's more just how you might think about electricity current "flow".

 

 

An analogy I heard once.  Think of the wire as a non-expanding pipe filled with incompressible fluid.  Push the fluid from one end, and fluid moves out the other end instantly.  No need for any mass to exceed speed of light.

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23 minutes ago, rocky500 said:

If he his correct, then it makes cable lifters quite a good promising addon. :)

 

 

Back in 1995 Stereophile Magazine commissioned Professor Malcolm Omar Hawksford to write a paper on the propagation of electromagnetic signals in stereo cables by solving Maxwell's equations in cable material from first principle. That article is here: https://www.stereophile.com/reference/1095cable/index.html 

 

That is the more rigorous approach. 26 years later we probably know more about material science today, and may be interesting to ask if we need to repeat that analysis again. 

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25 minutes ago, MLXXX said:

At Jefferson Lab, a typical energy for the electrons in the beam is 4 GeV which is 4 billion eV. That means the electron is traveling at 99.9999992% of the speed of light. Close but still not 100%.

 

 

Four GeV sounds like a lot, until you realise that one Joule (or one Watt second) is about 6.2*10^18 eV :) 

 

The clincher is that even though electrons are extremely lightweight, there are a huuuge number of them in an electron beam (or a piece of wire).

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3 hours ago, aussievintage said:

An analogy I heard once.  Think of the wire as a non-expanding pipe filled with incompressible fluid.  Push the fluid from one end, and fluid moves out the other end instantly.  No need for any mass to exceed speed of light.

Exactly.  So the charge is being carried by the electrons moving as a whole.  This is measured as the current.  However, even if this happens as fast as it possibly can (ie the speed of light) it does not explain the fact that in the scenario described that the light turns on (almost) immediately.  The only way to describe what happens is that when the circuit closes electromagnetic fields are created (and propogated) at the speed of light to convey power from the battery to the light bulb.  The time taken to turn the light on is therefore directly proportional to the distance between the battery and the light bulb, rather than the length of the circuit.

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14 hours ago, Stereophilus said:

Were there things that he represented that were incorrect?

To my mind the thought experiment setup relied on capacitative coupling to cause an initial relatively minor current flow. That is not normally the focus of power distribution.

 

Capacitative and inductive effects need to be considered in power distribution but you have to wait for the wave to pass along the transmission line to get usable power at the other end!

 

An interesting tutorial example but I feel a little off to the side compared with say sending a signal along loudspeaker cables, or distributing mains power.

 

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3 minutes ago, Stereophilus said:

Exactly.  So the charge is being carried by the electrons moving as a whole.  This is measured as the current.  However, even if this happens as fast as it possibly can (ie the speed of light) it does not explain the fact that in the scenario described that the light turns on (almost) immediately.  The only way to describe what happens is that when the circuit closes electromagnetic fields are created (and propogated) at the speed of light to convey power from the battery to the light bulb.  The time taken to turn the light on is therefore directly proportional to the distance between the battery and the light bulb, rather than the length of the circuit.

 

I think it does.  It is the movement of the fluid(current) that starts instantly in all parts of the circuit, hence the light starts instantly glowing due to power (I*I*R) being instantly dissipated in the resistance of the globe.

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1 hour ago, aussievintage said:

 

I think it does.  It is the movement of the fluid(current) that starts instantly in all parts of the circuit, hence the light starts instantly glowing due to power (I*I*R) being instantly dissipated in the resistance of the globe.

So a battery connected by a perfect circuit (ie no resistance, no voltage loss) to a light bulb located 1 light year away would light up instantly as well?

 

The way I understand it, it would take 1 light year for the propagated EM field to reach the light bulb when the battery is connected in this scenario.

 

In our universe nothing can travel faster than the speed of light.  Ie nothing is instantaneous (unless you want to discuss strange quarks).

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25 minutes ago, Stereophilus said:

 

In our universe nothing can travel faster than the speed of light.

But nothing is travelling that fast.  Back to the pipe analogy, you push some fluid in this end (at slow speed) and different  fluid comes out the other end, instantly (at slow speed).  Maybe the analogy breaks down for the electron flow.  Dunno, it's just how the idea was represented.

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6 minutes ago, aussievintage said:

Maybe the analogy breaks down for the electron flow. 

 

 

Answering myself.  Since it requires an electric field to act on an electron to move it,  I would have to agree this would still be speed of light (or some fraction) limited in it's propogation.

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