"Veritasium" (YT) - "The Big Misconception About Electricity" ?

[EEVblog]

Notes on simulation:

[rs20]

Yes, so shouldn't the Poynting vector be along the wires instead?
i.e. visually, how does the vector coming out of the battery know where the battery is physically?

I don't think there is a single Poynting vector, I think there are an infinite number of them corresponding to the infinite number of points in space where you could calculate it. However, if you take the integral over all points in space (add up all the infinitesimal vectors), the resulting "total" vector will end up pointing from the battery to the lamp. (If I understand correctly--I have no expertise in electromagnetics beyond the most elementary level.)

TL;DR: Not quite... see https://en.wikipedia.org/wiki/Surface_integral#Surface_integrals_of_vector_fields

It's a vector that's defined for all points in 3D space, you're absolutely right about that.

But integrating over all points in space makes little to no sense (for one thing, the units of the Poynting vector are W/m^2, but integrating across all three spatial dimensions would bring you up to W/m^2 * m^3 = W.m, rather than W.)

One correct way of using them is to divide space into two halves using a plane. Then integrate the Poynting vector* over the entire plane. That gives you a figure in W/m^2 * m^2 (integrating over only 2 dimensions) = W, and that figure (in Watts) tells you a very specific fact: how much power is flowing from one side of the plane to the other.

Or in a similar way, you can draw a sphere around the battery, integrate* over the surface of the sphere, and get the amount of power leaving the battery (assuming your sphere contains only the battery). Draw a sphere around the lamp, integrate* over that sphere, get the amount of power being consumed by the lamp. Etc etc.

* actually, pedantically, integrate the component of the Poynting vector normal to the plane/sphere

[Science Geek Grandpa]

As Derek said, energy flow happens when you have electric fields and magnetic fields.  If there is no current, there is no magnetic field, so no energy flow.  The Veritasium simulations don't have a switch, and he shows current happening instantaneously everywhere.  Would current move everywhere in the circuit when the switch is thrown?  I don't believe it.  So his Poynting Vector model is broken. 
As to the fundamental question of whether the power is transmitted in the wire or the space around the wire, imagine the bottom half of the circuit (as our moderator has sketched it) is completely surrounded by perfect shielding.  If Derek is right, no power should flow because the fields can't extend beyond the wire.  As the EEVblog simulation is formulated, the question is really: is the line coming into the bulb coupled to the line leaving the switch?  And the answer is yes, of course.  But does that mean the power is being transmitted by fields? 

[EEVblog]

As Derek said, energy flow happens when you have electric fields and magnetic fields.  If there is no current, there is no magnetic field, so no energy flow.  The Veritasium simulations don't have a switch, and he shows current happening instantaneously everywhere.  Would current move everywhere in the circuit when the switch is thrown?  I don't believe it.  So his Poynting Vector model is broken. 
As to the fundamental question of whether the power is transmitted in the wire or the space around the wire, imagine the bottom half of the circuit (as our moderator has sketched it) is completely surrounded by perfect shielding.  If Derek is right, no power should flow because the fields can't extend beyond the wire.  As the EEVblog simulation is formulated, the question is really: is the line coming into the bulb coupled to the line leaving the switch?  And the answer is yes, of course.  But does that mean the power is being transmitted by fields?

Shielding is a different question.
But otherwise, yes, the power is transmitted in the fields. A capacitor is an electic field.

[Bud]

Attached article provides a quantitative analysis which shows at DC condition Poynting  vector has two components, one along the surface of the wire in the direction of power transfer and the other one perpendicular to the wire directed into the wire, representing power loss dissipated inside the wire due to active resistance.

[EEVblog]

It had to be done.

[rs20]

Attached article provides a quantitative analysis which shows at DC condition Poynting  vector has two components, one along the surface of the wire in the direction of power transfer and the other one perpendicular to the wire directed into the wire, representing power loss dissipated inside the wire due to active resistance.

True enough as a statement on its own, albeit a little bit deceptive maybe.

But if you're trying to use this statement to discredit Veritasium's model, then no, you've only described the values of the Poynting vector exactly on the surface of the wire here. You've neglected to mention what's going on inside and outside the wires in that paper.

Inside the wire (s < a): Poynting vectors run perfectly radially inwards (eq 4), "suggesting" the power flow is just from the "true source of power [Poynting vectors outside the wire]" "burrowing" in from the surface of the wire to where they're needed to perform Joule heating/resistive losses. Zero contribution to carrying power from the battery to the load.
On the surface of the wire (s = a): Yes, two components, one along the surface of the wire in the direction of power transfer and the other one perpendicular to the wire directed into the wire. *But*, although you're correct that the component normal to the wire represents resistive power loss within the wire, you're wrong that the component running along the surface of the wire represents power transfer to the load.  Because the surface has no "thickness" to it, the integrated total power flow within this 2D surface running along that very same surface (as described here) is zero. I.e. the surface integral of a field that consists of vectors running only along that very surface is zero.
Outside the wire (s > a): Outside the wire, the same two components are present: a radial component that's generally heading towards resistive heating of the wire further down, and the component running along the wire. Now that we're in a full 3D region rather than the 2D surface of the wire, we can draw a plane separating our battery from our load and compute the power carried outside the wire.

Performing the process described here, to break down the power carried from the battery to the load into the three different regions in/around the wire:

Inside the wire (s < a): P = 0 (no Z-component)
On the surface of the wire (s = a): P = 0 (intersection of surface with plane is 1D circle not 2D region)
Outside the wire (s > a): P = nonzero, and I can only presume it would work out to I*V, the power dissipated in the load

The one thing I will grant you though is that if you look at fig 6, you can see that the majority of the content of the Poynting vector is quite close to the wire, because both the E and H fields are strongest there. So I wouldn't be surprised if Veritasium's video had the Poynting vectors drawn a little far from the wires to be truly non-deceptive. Not sure though, the full circuit case might be different. But, it's still true that under the strict interpretation of Maxwell's laws/Poynting vectors, the full entirety of the power is carried outside the wire. (According to that paper at least).

It had to be done.

Truly a thing of beauty

[G7PSK]

This was done in an even simpler form a year ago.https://youtu.be/C7tQJ42nGno

[sectokia]

I still don't quite get his explaination at 7:35
He shows the Poynting vector S coming out from the battery in a DC circuit. How? There is no EM radiation loss.

What you call EM radiation loss is actually just part of a transmission line acting as a load, and simply consuming the energy and converting it to photons, just like the light bulb does.

A Poynting vector does *not* mean radiation is being emitted in that direction. It shows the flow of energy. There is a big difference. Consider a bar magnet with a charge near its center. The B field will be from north to south, but the E field will be outwards from the middle. The Poynting vectors thus point around in circles, there is a flow of energy around and around! There will not be EM photons being ejected at a tangent to the circles.

If you want a good 'mind model' for what is going on, I suggest this:
-Light / EM radiation is photons in their particle form. They occupy a point in space. They move from point to point through 3D space as a ball does.
-Energy flow in fields is photons in their wave form. They occupy all of space they do not move but flutter out of existence in one  are and into existence in other and their momentum to do so is the Poynting vector.

[GlennSprigg]

Dear eti... Yes, Veritasium is indeed a generally very clever & knowledgeable man, and often goes above & beyond
in explaining/demonstrating all manner of topics. However, sometimes 'we' (humans), get too tied up with semantics,
and nomenclature that go beyond  the acronym 'KISS', "Keep it simple stupid"!, and then basics are lost... 

[snarkysparky]

It seems many posters here accept the idea that the poynting vector in this DC circuit does in fact indicate power flowing outside the wire.

I can't wrap my head around this proposal.   What this would be saying is that in the space around the wire and at a point where the poynting vector is positive there is a power flow density at that point.

What mechanism would be transferring power at the location in air where the poynting vector is positive in the DC circuit.

[Bud]

Same mechanism as for AC case, no difference, since for both cases the Poynting vector is a cross product of electric and magnetic field vectors S=E*H.

[Kalvin]

One thing that Dave is saying in this video is contradicting the reality. He says numerous times in the video that there is nothing new in Veritasium's video for electrical engineers, and that practicing engineers do know this EM-field stuff already etc. Dave also states that in practice it is sufficient to think that the energy flows along the wires, and typically only high frequency engineers need to think about EM-field stuff.

My counter-argument is this: If Dave's argument is true, we would not have EMI, grounding, ground-loop, signal-integrity etc. issues in our circuits, because if practicing engineers really knew and understood how the EM-fields were actually flowing in the circuits, they would not make that many troublesome designs.

Since in practice we see way too often designs that have these kind of issues, it is clear that a) practicing engineers do not really understand EM-fields, and b) it is not really sufficient to think that the energy flows only along wires.

[Bud]

you're wrong that the component running along the surface of the wire represents power transfer to the load.

I did not say that, it was your interpretation, which you entitled to since it it is hard to type engineering essays on a tablet, lol, so I used simpler wording.

[snarkysparky]

Wiki article for Poynting vector.  Particularly the section on static fields.
Speaks of only conservation of angular momentum.  We know that static fields imply stored energy.  Not necessarily steady state energy transfer.    There are many articles on the interpretation of poynting vector for static fields.  Most behind a paywall though.
I haven's seen any support for actual steady state energy transfer in a static field situation.  Remember that even though current is flowing in the wire the field magnitudes and direction are constant values at a point in space between the wires.

from Wiki...
The consideration of the Poynting vector in static fields shows the relativistic nature of the Maxwell equations and allows a better understanding of the magnetic component of the Lorentz force, q(v × B). To illustrate, the accompanying picture is considered, which describes the Poynting vector in a cylindrical capacitor, which is located in an H field (pointing into the page) generated by a permanent magnet. Although there are only static electric and magnetic fields, the calculation of the Poynting vector produces a clockwise circular flow of electromagnetic energy, with no beginning or end.

While the circulating energy flow may seem unphysical, its existence is necessary to maintain conservation of angular momentum. The momentum of an electromagnetic wave in free space is equal to its power divided by c, the speed of light. Therefore the circular flow of electromagnetic energy implies an angular momentum.[16] If one were to connect a wire between the two plates of the charged capacitor, then there would be a Lorentz force on that wire while the capacitor is discharging due to the discharge current and the crossed magnetic field; that force would be tangential to the central axis and thus add angular momentum to the system. That angular momentum would match the "hidden" angular momentum, revealed by the Poynting vector, circulating before the capacitor was discharged.

[bpiphany]

A static field still has flow. Whether or not there is flux entering or leaving the system in a point should be down to the divergence of the field being zero or not. The battery is a source to the "poynting field" and the load a sink to it.

The sketch by rfeeces actually converted me a bit. In the steady state most of the E-field will be between the source and sink. The very long stretches of (resistance free) wires on each side of the load will be at the same potential half the way to the moon and back. Hence the E-field will mostly be zero along the stretch, and most of the poynting field flux should take the shortcut straight across the air gap between source and sink where the E-field has a non-zero value.
https://www.eevblog.com/forum/chat/veritasium-(yt)-the-big-misconception-about-electricity/msg3829871/#msg3829871
What the picture looks like in the dynamic system, breaking or making contact, is another story.

In the case where the circuit has the source at one end and the sink at the other end of the system, like the diagram in the Veritasium video [edit: the RGB fancy one with the field lines], the ExB-field should bunch up more along the wires. The electric potential of the two leads is constant along their length, and the E-field flowing perpendicular between them, and perpendicular to the B-field the current in them generate.

[SiliconWizard]

My counter-argument is this: If Dave's argument is true, we would not have EMI, grounding, ground-loop, signal-integrity etc. issues in our circuits, because if practicing engineers really knew and understood how the EM-fields were actually flowing in the circuits, they would not make that many troublesome designs.

Since in practice we see way too often designs that have these kind of issues, it is clear that a) practicing engineers do not really understand EM-fields, and b) it is not really sufficient to think that the energy flows only along wires.

It's not necessarily a matter of not understanding EM fields though. It's essentially a matter of any real-world system being HARD to model, and determining when a simple model is adequate and when it is not is also a difficult matter. Another issue when strictly using circuit analysis - as most of us do - and that was pointed out in the famous KVL thread, is that finding a proper lumped model for a given circuit operating in EM fields is HARD too. So we use a lot of rules of thumb.

As to how electrons "flow" in a conductor, this is still a non-trivial point at all and far from being what we are usually taught, and that should be the key point in Veritasium's video. I'm not 100% sure his circuit example is fully relevant to illustrate the point though.

[Kalvin]

My counter-argument is this: If Dave's argument is true, we would not have EMI, grounding, ground-loop, signal-integrity etc. issues in our circuits, because if practicing engineers really knew and understood how the EM-fields were actually flowing in the circuits, they would not make that many troublesome designs.

Since in practice we see way too often designs that have these kind of issues, it is clear that a) practicing engineers do not really understand EM-fields, and b) it is not really sufficient to think that the energy flows only along wires.

It's not necessarily a matter of not understanding EM fields though. It's essentially a matter of any real-world system being HARD to model, and determining when a simple model is adequate and when it is not is also a difficult matter. Another issue when strictly using circuit analysis - as most of us do - and that was pointed out in the famous KVL thread, is that finding a proper lumped model for a given circuit operating in EM fields is HARD too. So we use a lot of rules of thumb.

As to how electrons "flow" in a conductor, this is still a non-trivial point at all and far from being what we are usually taught, and that should be the key point in Veritasium's video. I'm not 100% sure his circuit example is fully relevant to illustrate the point though.

Quite often the encountered problems are pretty obvious and would have been preventable in the first place if the engineers were familiar with the established industry practices and/or would have been thinking in terms on EM-fields, like how the currents will flow in the circuit on a PCB, how the wiring affects signal integrity, how the poor wiring may cause EMI, how the magnetic fields generated by the inductive components will couple nearby sensitive components, signal traces and wirings etc.

[MIS42N]

Very interesting. The video is, of course, wrong. In the scenario, the primary transfer of energy is electrostatic. An electron moves, like charges repel, the electron next to the moving electron moves. Propagates through an electrical conductive medium. Eventually an electron near the light bulb is required to do work and the bulb lights.

The EM field is a side effect. In fact, there is no E field, Maxwell's equations have it as a mathematical convenience because that's how it seems to be. The Magnetic field is the only reality. When a magnetic field interacts with a charged body, the charged body is affected. When a charged body moves, it interacts with the magnetic field. So it appears there is a transfer of E from one place to another. No charged body, no E field. Our environment is full of electrons and protons all of which are affected by, and affect, magnetic fields. So the E field appears as a consequence of the M field.

Back to the scenario. When the switch is thrown, some electrons move to re-balance the electrostatic difference between one side of the switch and the other. To do so, they create a changing magnetic field. Some of that magnetic field interacts with the parallel conductor causing a movement of electrons in that conductor. The effect will be trivial and dependent on the physical arrangement of conductors and the ability of the magnetic field to propagate between them. This is what is described by capacitance.

In the meantime, the electrostatic field is trying to push electrons through the long conductors. When the electrons try to move they use energy to establish a change in the M field. This is what is described by inductance. Consequently the "push" cannot travel at the speed of light. So the bulb will light up some time later than 1 second. All of which is calculable using values and formula that describe what happens.

[penfold]

[...]
My counter-argument is this: If Dave's argument is true, we would not have EMI, grounding, ground-loop, signal-integrity etc. issues in our circuits, because if practicing engineers really knew and understood how the EM-fields were actually flowing in the circuits, they would not make that many troublesome designs.

Since in practice we see way too often designs that have these kind of issues, it is clear that a) practicing engineers do not really understand EM-fields, and b) it is not really sufficient to think that the energy flows only along wires.

In a world where EMI etc was the only objective in all designs, then sure, that argument would be absolutely true. Not saying it's false in its reasoning, but maybe not the only conclusion you can draw. We would probably also have to assume that all designs produced from a true understanding of EM would also meet thermal, mechanical, cost, and functional constraints... and still meet all of those constraints when the sales team decide what they actually wanted was a plastic enclosure and have it delivered the week previous. It's always a balance and most engineers are unfortunately humans: mistakes and carelessness happen, things get overlooked with different priorities, it doesn't say anything about their understanding.

[Vtile]

It was a bit disappointing, Oliver was shown, but not mentioned alas everything relates in that video directly to him ..sneaky.

[Vtile]

I think I will chose "nothing above" as afterthough, because such dimpulp that can pickup the transient phase should also be lit all the time by the currents introduced by such lenghty wire rotating and moving through magnetic fields of solarsystem.

[SiliconWizard]

While in the end, there's nothing new in this video, I agree with Dave in that Veritasium left a number of details out. The video is clearly not for EEs nor for physicists. Possibly it is for people having a scientific background but nothing too advanced. It does give some food for thought, such as what is really energy and how does it flow, but it's kind of a byproduct of the video. (Which hey, is still something!) That may even get some people to get interested in quantum stuff maybe - although again the video doesn't really mention that. Why not!

One pretty "disappointing" part of the video was the conclusion with the "answer". Not only does the guy not really explain his answer fully, but it gets worse when he starts talking about the bulb "not getting full power immediately" and impedance of the cable, and... At this point you're like: what is transmitted after 1/c s exactly? And are we sure we're even all understanding what the question was initially, including himself?

And the example circuit... yeah why not. But why resort to using such a large line for his example? This would be exacly the same with a much smaller line, just get your figures in proportion. Likewise, he talks about doing an experiment like this in the desert with some funding (was he calling for money? ), while it can be done in a lab with a few meters of cable and a decent scope. Now the setup would not be trivial though: you need to be synchronized properly on both ends of the circuit and not let EM fields themselves disturb your measurements - so this would be full of traps.

So, yeah. But it still triggers discussion and some additional thoughts, so it's not bad for this purpose.

[SiliconWizard]

But otherwise, yes, the power is transmitted in the fields. A capacitor is an electic field.

Yes, that explains how power flows through a capacitor. Rings a bell.

[niconiconi]

Buildings have walls and halls.
People travel in the halls, no the walls.
Circuits have traces and spaces.
Energy travels in the spaces, not the traces.
- Ralph Morrison

+1. This is a fairly standard description used by many authors on electromagnetics, RF/microwave, and EMI/EMC (although for low-frequency and steady-state DC circuits, it has little practical use and is more of an academic exercise). I think it provoked strong reactions mostly because the "everything you know is wrong" & "pure theory over practice" shock video presentation style, rather than anything fundamentally controversial (there isn't any) about the field-centrc view on electrical circuits.

Examples...

Henry W. Ott. Electromagnetic Compatibility Engineering. John Wiley & Sons, 2009, Chapter 5, Section 6, page 215.

When conductors become long, that is, they become a significant fraction of the wavelength of the signals on them, they can no longer be represented as a simple lumped-parameter series R–L network [...] Under these circumstances, the signal conductor and its return path must be considered together as a transmission line, and a distributed-parameter model of the line must be used.
[...]
The important concept to understand is that we are moving an electromagnetic field, or energy, from one point to another, not a voltage or current. The voltage and current exist, but only as a consequence of the presence of the field.
[...]
It is important to note that what travels at, or close to, the speed of light on a transmission line is the electromagnetic energy, which is in the dielectric material not the electrons in the conductors. The speed of the electrons in the conductors is approximately 0.01 m/s (0.4 in./s) (Bogatin, 2004, p. 211) which is 30 billion times slower than the speed of light in free space. In a transmission line, the most important material is therefore the dielectric through which the electromagnetic energy (field) is propagated, not the conductors that are just the guides for the energy.

Thomas H. Lee, Planar Microwave Engineering, Cambridge University Press, 2004, Chapter 21, Section 2, page 690,

Now the electric field inside a perfect conductor is zero. So, by Poynting’s theorem, no (real) energy flows inside such a wire; if there is to be any energy flow, it must take place entirely in the space outside of the wire. Many students who comfortably and correctly manipulate Poynting’s theorem to solve advanced graduate problems in field theory nonetheless have a tough time when this particular necessary consequence is expressed in words, for it seems to defy common sense and ordinary experience (“I get a shock only when I touch the wire”).

The resolution to this seeming paradox is that conductors guide the flow of electromagnetic energy. This answer may seem like semantic hair-splitting, but it is actually a profound insight that will help us to develop a unified understanding of wires, antennas, cables, waveguides, and even optical fibers. So for the balance of this text (and of your professional careers), retain this idea of conductors as guides, rather than conduits, for the electromagnetic energy that otherwise pervades space. Then many apparently different ways to deliver electromagnetic energy will be properly understood simply as variations on a single theme.

William H. Hayt, Jr. . John A. Buck, Engineering Electromagnetics, McGraw-Hill, 1989, Chapter 11, Section 5, Page 360,

Electromagnetic energy is not transmitted in the interior of a conductor; it travels in the region surrounding the conductor, while the conductor merely guides the waves. The currents established at the conductor surface propagate into the conductor in a direction perpendicular to the current density, and they are attenuated by ohmic losses. This power loss is the price exacted by the conductor for acting as a guide."

Standard Handbook for Electrical Engineers, 11th Edition, Fink, Donald G. editor, McGraw-Hill, Chapter 2, Section 40, Page 2-13

The energies stored in the fields travel with them, and this phenomenon is the basic and sole mechanism whereby electric power transmission takes place. Thus the electrical energy transmitted by means of transmission lines flows through the space surrounding the conductors, the latter (conductors) acting merely as guides.
[...]
The usually accepted view that the conductor current produces the magnetic field surrounding it must be displaced by the more appropriate one that the electromagnetic field surrounding the conductor produces, through a small drain on its energy supply, the current in the conductor. Although the value of the latter (current) may be used in computing the transmitted energy, one should clearly recognize that physically this current produces only a loss and in no way has a direct part in the phenomenon of power transmission.

Richard Feynman, The Feynman Lectures on Physics, Volume II, Chapter 27 Field Energy and Field Momentumld Energy and Field Momentum.

As another example, we ask what happens in a piece of resistance wire when it is carrying a current. ... . . There is a flow of energy into the wire all around. It is, of course, equal to the energy being lost in the wire in the form of heat. So our crazy theory says that the electrons are getting their energy to generate heat because of the energy flowing into the wire from the field outside. Intuition would seem to tell us that the electrons get their energy from being pushed along the wire, so the energy should be flowing down (or up) along the wire. But the theory says that the electrons are really being pushed by an electric field, which has come from some charges very far away, and that the electrons get their energy for generating heat from these fields. The energy somehow flows from the distant charges into a wide area of space and then inward to the wire.

... that the energy is flowing into the wire from the outside, rather than along the wire.