The Big Misconception About Electricity

hhtat

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Veritasium is known to be the click-bait of science and does a lot of pseudoscience-like logic in other videos so I would take this video was a truckload of salt. Honestly, he just discovered RF & maybe capacitance. The whole water flowing through pipes analogy still holds.
 

Posplayr

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Veritasium is known to be the click-bait of science and does a lot of pseudoscience-like logic in other videos so I would take this video was a truckload of salt. Honestly, he just discovered RF & maybe capacitance. The whole water flowing through pipes analogy still holds.
I'm not sure what would be pseudoscience in this video, but it also doesn't know what would constitute (as the title suggests) a "misperception" about electricity?

Is it that Maxwell's equations should be not to apply to a simple electrical circuit.
That there is some common belief that Ohms law suspends the validity of maxwell's equations?
That until we applied Poynting's principle to a circuit we would have thought that there was an inconsistency with Maxwell and conservation of energy?

Maybe Veritasium is trying to make us think that the electrical power travels only through the Poynting flux and not through the wires?

Now there is this semi idealized question posed in the video about the battery and light being close and the wires being far away. Veritasium did warn that some "reasonable" simplifying assumptions must be made which leaves a lot of wiggle room for interpretations, but it is apparently enough to draw into question the final results from 4 Professors of EE.

So if there is a pseudoscience, it is in his somewhat "sleight of hand" in going from well-understood science (Ohm's, Maxwell and Poynting), to the surprising 3-dimensional integrated view in an electrical circuit, but then adding in some relativistic factors about very long lengths of wire with zero capacitance, inductance, and resistance (as corresponding simplifying assumption??).

This is kind of like the model of white noise that has infinite bandwidth but finite power spectral density which mathematically would have infinite variance (i.e. it is a physical impossibility of an idealized model).
 
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hhtat

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Maybe Veritasium is trying to make us think that the electrical power travels only through the Poynting flux and not through the wires?
That's exactly what they're trying to imply.
Veritasium did warn that some "reasonable" simplifying assumptions must be made which leaves a lot of wiggle room for interpretations, but it is apparently enough to draw into question the final results from 4 Professors of EE.
Being correct on a technicality means you've to dive into minute details of the argument which is the opposite of simplifying assumptions. I bet those there professors of EE would have serious problems with the final video...
So if there is a pseudoscience, it is in his somewhat "sleight of hand" in going from well-understood science (Ohm's, Maxwell and Poynting), to the surprising 3-dimensional integrated view in an electrical circuit, but then adding in some relativistic factors about very long lengths of wire with zero capacitance, inductance, and resistance (as corresponding simplifying assumption??).
There's a bunch of sleight of hand that is just meant to distract.

One example is around 6:30 mark where they say that the electrical field from the battery extends through the wires and induces a flow of electrons (kinda correct but doesn't explain what "extending the electrical field" means - should've describe how both the wires and the bulb have more free electrons than the air). Then it says this flow causes surface charges to build up on the wire (no, that's flat out wrong, it's not due to the flow). But then it says these surface charges causes electron to flow. I thought they were already flowing and creating the surface charges? So what is it?

Anyway, the main slight of hand is the idea that Poynting vector calculates a physical process that is happening in 3D space. The flow of energy isn't a physical process. There's no particle, waves or forces behind this flow of energy. It is akin to using some market metrics to calculate exactly how money is moving through the stock market.
 

hhtat

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Say what?
Maybe "physical process" isn't the term I'm looking for. I think what I'm trying to say is energy flow in itself isn't a physical process but a measure of the change in a quantitative property caused by physical process if that makes any more sense.

In physics, energy is the quantitative property that must be transferred to a body or physical system to perform work on the body, or to heat it. It most definitely is a physical process.
You're correct energy is a quantitative property and the flow of energy is a change in that quantitative property over space and time.
 

robby

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If you add two more switches to the circuit at opposite ends where the wire bends - and open those two switches half a second before you flip the main switch - you'll still see some RF (+ maybe capacitance?) induced voltage at the bulb even thought the circuit is incomplete.

Again, I find this video extremely misleading. It's correct on a technically but it doesn't state it that way. Instead it states it in the way that "electrical energy doesn't flow through wires."
Agree that it is very misleading. The electromagnetic properties are being looked at separately which is fine in a technical argument but will give people the wrong impression of how this would work in a practical sense.
 

hhtat

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energy is the quantitative property
I also want to mention that the video did a qualitative analysis of energy flow instead of a quantitative one. In the other words, that 3D diagram reflects direction of the fields and the Poynting vector with no analysis of the magnitudes. They then go on to suggest that majority of energy flows through free space outside the wires
 
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Posplayr

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I also want to mention that the video did a qualitative analysis of energy flow instead of a quantitative one. In the other words, that 3D diagram reflects direction of the fields and the Poynting vector with no analysis of the magnitudes. They then go on to suggest that majority of energy flows through free space outside the wires
I think the notion that we understand the underlying physical processes is a fallacy. Even if we are the best-known model in quantum mechanics and string theory we don't know the exact physical process we only have models of these processes. Ohms law is one such model as are Maxwell's and Poynting's. Arguing that energy is transferring via a field theory and not via a circuit is as fundamentally flawed as arguing the reverse (i.e. energy is transferred via current flow and not through a field).

In both cases there are limits to these models, the most obvious example is when I consider my MIG welder. There is this spray of plasma that comes from the wire (or can be reversed) that is either DC or AC and it is hard to imagine that there is no "real" energy transfer regardless of the AC/DC direction of flow. The metal gets very hot early indicating heat/energy transfer but I suspect the ionized air and plasma flow do not exactly fit into a field /Poynting flux model any more than ohms law other than in a gross aggregate sense. Quite simply there is a more complex fundamental particle model that would better describe what is going on.

I'm also reminded of similar instances of misperceptions of established engineering principles in aerodynamics. The common model used for generating lift on a wing is that the air on the top of the wind travels faster than the bottom and therefore due to Bernoulli there is a lower pressure on top and therefore an associated lift. The mental crutch to explain this (although patently false) is that the wings are curved and therefore the path on the upper side of the wing has further to go which results in the lift. However, it can be demonstrated that even a flat plate will produce lift and the explanation for the lift is circulation (i.e. chordwise circulation with the upper flow directed in the direction of flight).
As I sit here writing this I realize that the notion of curved upper part causes lift is actually not 100% false. This is because curved winds (i.e. with camber) exhibit higher lift coefficients. This is why commercial aircraft have trailing edge flaps that are deployed at landing.

To wrap this up it would seem that in general there will always be a breakdown in our models under some condition requiring a more general model (at least until a Theory of Everything is developed). But within their respective regions of application, models such as Ohm's, Maxwell's, and Poynting do apply to real processes and one is not to be applied as "the only answer" to the exclusion of the others.
 

Posplayr

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But if not confined by the math and tools, strictly for engineering purposes, having ones mind blown is fun.
Eric Dollard
My mind is not blown by the physics but by how this graphical representation so precisely matches one of the most fundamental innermost models of our most formal logic (i.e. the propositional calculus).
 

hhtat

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To wrap this up it would seem that in general there will always be a breakdown in our models under some condition requiring a more general model (at least until a Theory of Everything is developed). But within their respective regions of application, models such as Ohm's, Maxwell's, and Poynting do apply to real processes and one is not to be applied as "the only answer" to the exclusion of the others.
True but they're using Poynting vector for something it doesn't describe. It's not a breakdown of that model. It's a misuse.
 

Posplayr

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True but they're using Poynting vector for something it doesn't describe. It's not a breakdown of that model. It's a misuse.
I'm not sure why you think the Poynting vector does not apply in general? The vector is the basis for the Poynting Theorem which is an energy balance in terms of the vector. The theorem does not only apply to free space.

In words, the theorem is an energy balance:

The rate of energy transfer (per unit volume) from a region of space equals the rate of work done on a charge distribution plus the energy flux leaving that region.

A second statement can also explain the theorem - "The decrease in the electromagnetic energy per unit time in a certain volume is equal to the sum of work done by the field forces and the net outward flux per unit time".

If you read beyond the section above to "Generalization" there is even a "mechanical energy" counterpart which would imply a shared inner model

Another interesting aspect is that spect to the general nature of applicability:

"In a macroscopic medium, electromagnetic effects are described by spatially averaged (macroscopic) fields. The Poynting vector in a macroscopic medium can be defined self-consistently with microscopic theory, in such a way that the spatially averaged microscopic Poynting vector is exactly predicted by a macroscopic formalism. This result is strictly valid in the limit of low-loss and allows for the unambiguous identification of the Poynting vector form in macroscopic electrodynamics.[4][5]"

 
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hhtat

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The rate of energy transfer (per unit volume) from a region of space equals the rate of work done on a charge distribution plus the energy flux leaving that region.
A second statement can also explain the theorem - "The decrease in the electromagnetic energy per unit time in a certain volume is equal to the sum of work done by the field forces and the net outward flux per unit time".
The Poynting vector needs to be integrated over a closed surface of a volume in 3D space to be used in the Poynting theorem.

Yes there's non-zero Poynting vectors outside the wires and yes there shouldn't be any vectors inside the wire (assuming ideal conductors, etc). But I don't know what you can conclude from that without drawing a volume somewhere and integrating the vectors over the closed surface of that volume. If you do that outside the wires... you should get zero. If you do that inside or including the wire... you should get zero. It should be zero unless you include an electromagnetic energy source or sink inside the volume.
 

Posplayr

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Having read a little more, it would seem that the video is pushing the illusion that the energy travels in the fields and not the circuit and that somehow despite the lengthy extension of the wire. the Poynting vector is going to take the shortest path and avoid the long circuit. Yes, the average distance of where the work is done (lighting the light) is short (the shorter distance) but the field propagation is along the wire which has to travel the full length of the circuit.

Perhaps this is the caveat to the notion of Poynting Flux in that it is a measure of the work based on a net movement and not a function of the actual path to achieve that. There are apparently path-dependent (constrained paths) and path-independent forms of work.



In any event, to compute a propagation delay based on teh shorter path would violate Maxwell's equations that say the existence of current in a wire is associated with the corresponding electric and magnetic fields. So while it is not impossible to have E&M fields separated from current in a wire (i.e. in free space propagation of light), in this particular case all E&M waves are associated with the current so there is not going to be any "shortcutting" based on path length between battery and light.

So if in a standard application of the theory, the answer to the question is quite clear, then we would have to conclude that the question posed that is supposed to be some great quandary (by the EE professors) is more click bate ! The only mystery is in the simplifying assumption about infinite wires with zero inductance, capacitance, or resistance.
 

Posplayr

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The Poynting vector needs to be integrated over a closed surface of a volume in 3D space to be used in the Poynting theorem.

Yes there's non-zero Poynting vectors outside the wires and yes there shouldn't be any vectors inside the wire (assuming ideal conductors, etc). But I don't know what you can conclude from that without drawing a volume somewhere and integrating the vectors over the closed surface of that volume. If you do that outside the wires... you should get zero. If you do that inside or including the wire... you should get zero. It should be zero unless you include an electromagnetic energy source or sink inside the volume.
Isn't the light an energy sink? I would assume that the graphic was generated from a numerical integration package that would compute the fields from an idealized circuit.

You said before "It's a misuse." Where or what it's abusing the model?
 

hhtat

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Isn't the light an energy sink? I would assume that the graphic was generated from a numerical integration package that would compute the fields from an idealized circuit.
Are you talking about the 3D graphic from the original video? It most likely wasn't created that way...

You said before "It's a misuse." Where or what it's abusing the model?
Trying to interpret the Poynting vector as something it's not.

Consider this example: wrap the entire circuit loop in a perfect shield. Assuming no changing magnetic field... Poynting vector is always zero inside a perfect conductor so zero inside the shield.

When you follow the energy flux lines from battery to blub there's this large almost 1 meter gap starting from the inner surface of the shield on the battery side and ending at the inner surface of the shield on the bulb side. If you follow the same logic as the video (a misuse) then you totally changed how energy was transferred from battery to bulb as there's no direct paths anymore.

In practice... you'll find this does little to how the circuit operators (sans some small RF & capacitance effects which he relies on for the technically correct answer to original question). More importantly, any of the closed surfaces you integrated over before adding the shield should still result in the same answers.
 
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Posplayr

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onsider this example: wrap the entire circuit lo
Unfortunately, I think this your example is getting away from any point I can absorb.

More from Wikipedia:
gives an expression for the Poynting vector:
{\mathbf  {S}}={\mathbf  {E}}\times {\mathbf  {H}},

which physically means the energy transfer due to time-varying electric and magnetic fields is perpendicular to the fields

This quote specializes in the application to time-varying E and H, which I doubt is an exclusive application of the Poynting vector. If we take the equation quite literally it says if there are any non-colinear E and H fields, then there is a non-trivial Poynting vector and associated energy flux.

My conclusion is that: Since the E and H fields are static or dynamic in a 3-dimensional space, it implies that the Poynting vector exists and is also a 3-dimensional function at whatever localized position in 3-D space that it is evaluated.

I guess it is certainly possible to misapply any theory, but I fail to see any particular application where the Ponting vector is inapplicable save for the colinear case mentioned above where the cross product does to zero.

This picture on Wikipedia is essentially the same example as the video other than a resistor is used in place of the light. Maybe the video adapted this picture and so whatever error you are seeing is not from the video but rather from Chetvorno, King of Hearts (the Wikipedia author)
800px-Poynting_vectors_of_DC_circuit.svg.png

English: A simple DC circuit consisting of a battery (V) and a resistor (R), showing the Poynting vectors (S, blue arrows) in the space surrounding it, as well as the fields it is derived from, the electric field (E, red arrows) and the magnetic field (H, green arrows). The Poynting vector {\displaystyle \mathbf {P} =\mathbf {E} \times \mathbf {H} }
{\displaystyle \mathbf {P} =\mathbf {E} \times \mathbf {H} }
represents the direction and magnitude of the power flow in the electromagnetic field (the length of the vectors shown here are not to scale; only the direction is being shown) In the region of space around the battery, the Poynting vectors are directed outward, indicating that power flows out from the battery into the electromagnetic field. In the region of space around the resistor, the Poynting vectors are directed inward, indicating that since the resistor consumes power, the power enters it from the field. On any plane (P) located between the battery and the resistor, it can be seen that the power flux though the plane is directed toward the resistor.

 

SpongeboB Sinewave

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Main Issue I have is with the multiple choice answer of 1/C which could have been specified a bit clearer. 1/~300,000,000 meters per second over the length of the wires that is.

BTW, take the wire away and see how far/fast the energy from the battery gets from A to B. 😁
 
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