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

[EEVblog]

I think the "clickbating" aspect of his videos are of secondary importance. In this other video he discusses how misconceptions restrain people's ability to learn. That's why all Vertitasium videos start discussing the misconception first and then they introduce the scientific concept about the topic, because he saw that, that way, people invest mental effort in watching his videos and actually learn.

His PhD thesis was literally on this topic:
https://www.sydney.edu.au/science/physics/pdfs/research/super/PhD(Muller).pdf

[adx]

I think the "clickbating" aspect of his videos are of secondary importance. In this other video he discusses how misconceptions restrain people's ability to learn. That's why all Vertitasium videos start discussing the misconception first and then they introduce the scientific concept about the topic, because he saw that, that way, people invest mental effort in watching his videos and actually learn.

His PhD thesis was literally on this topic:
https://www.sydney.edu.au/science/physics/pdfs/research/super/PhD(Muller).pdf

We were all set up! In some kind of quasi-acausal ultra-thesis experiment, of which we were only partly aware prior and nearly but incompletely aware during. Now I know where my "Neo and the Architect" screens scene sense came from. Is it even a set up if it is correct? Can we complain if we wanted to participate? If it was all explained in a video, one I probably watched but skimmed or forgot? So many questions I wouldn't want to even ask in non rhetorical form in case they were unnecessary.

But it certainly has shone a light on the industrial cat amongst the academic pigeons. It's good that someone is trying to improve the system. As in, properly / from the inside. And in general, there seems to be a change in the wind, with choice of media that is far more involving than going to a lecture hung over with broken beerbottles and subtle aromas dripping from your bag.

I haven't conveniently forgotten my answers for SiliconWizard. Just got stuck trying to draw a vacuum, and then a 3D section view callout for it. I'm not a mechanical engineer.

[SiliconWizard]

The point, is, again, to see if the original example in Veritasium's video is really relevant in showing what was claimed when the system reaches steady state.

The question was clearly intended toward getting the 1/c instant response.

Sure, but that's like running in circles... =)
Actually, the video you posted kind of answered that, but question is, what amount of energy exactly would be transfered from one wire section to the facing one (so without traveling along the whole wire loop) once the system has reached steady state.

[SilverSolder]

I have a quick question, maybe someone can help me understand:

What happens if we put the bulb inside a steel Faraday cage?  That would mean an outside electrical field cannot reach it, and any magnetic field would not reach the bulb either (it would by-pass the bulb via the steel box).

If the Veritasium video is right and the energy is carried by the magnetic/electric field and not the wire itself...   wouldn't that mean the bulb would not be able to light up inside the Faraday / magnetic shield cage?  (Similarly, we could put the battery inside a steel box, or both...)

[Alex Eisenhut]

 

[rfeecs]

I have a quick question, maybe someone can help me understand:

What happens if we put the bulb inside a steel Faraday cage?  That would mean an outside electrical field cannot reach it, and any magnetic field would not reach the bulb either (it would by-pass the bulb via the steel box).

How would the wires get from the outside to the inside of the Faraday cage?

[SilverSolder]

I have a quick question, maybe someone can help me understand:

What happens if we put the bulb inside a steel Faraday cage?  That would mean an outside electrical field cannot reach it, and any magnetic field would not reach the bulb either (it would by-pass the bulb via the steel box).

How would the wires get from the outside to the inside of the Faraday cage?

0.01mm holes drilled through the 5cm thick steel box for a thin, insulated wire.   Drilled from two sides at an angle, so there is no direct flux path through.

[rfeecs]

The energy would pass through the insulation around the wires.

[HuronKing]

What if an infinite conducting sheet is placed between the source and load? It's the same thing as Silversolder's question and it is answered in Kraus' Electromagnetism, Chapter 10. You've built a waveguide:

https://physics.stackexchange.com/questions/435041/poyntings-vector-and-its-application-to-circuits

And this is one of the biggest problems in designing waveguides. How do you get the signal into the waveguide without reflection or radiation at the connection point? Impedance matching.

[SilverSolder]

The wires are very thin, 0.01mm, just enough to light a small bulb.  The insulation is the thinnest possible layer of vacuum that you can have without flashing over (a few micrometers), and the box is at least 500mm thick.

I am struggling to understand how the fields will be able to carry energy to the bulb.  And if they do make it in...  wouldn't the tortuous path they have to take to get there mean there would be more resistance, compared to a layout that does not impede the fields in any way?

[rfeecs]

I am struggling to understand how the fields will be able to carry energy to the bulb.  And if they do make it in...  wouldn't the tortuous path they have to take to get there mean there would be more resistance, compared to a layout that does not impede the fields in any way?

Nope.

[SilverSolder]

I am struggling to understand how the fields will be able to carry energy to the bulb.  And if they do make it in...  wouldn't the tortuous path they have to take to get there mean there would be more resistance, compared to a layout that does not impede the fields in any way?

Nope.

How would you draw the magnetic lines of force in this example?   I really am struggling to see it.  I'm probably overlooking something obvious.

[ogden]

I am struggling to understand how the fields will be able to carry energy to the bulb.

As current which will light the bulb is purposefully not specified, you can get as creative with wire diameter as as you want. As long as single electron can squeeze through, challenge is still valid.

[rfeecs]

How would you draw the magnetic lines of force in this example?   I really am struggling to see it.  I'm probably overlooking something obvious.

It would be like a coaxial cable with a very thin dielectric.

[bdunham7]

I am struggling to understand how the fields will be able to carry energy to the bulb.  And if they do make it in...  wouldn't the tortuous path they have to take to get there mean there would be more resistance, compared to a layout that does not impede the fields in any way?

In the DC case, no matter how you encase the circuit or what external static fields you apply, the Poynting math always miraculously works out to the same end solution that matches DC circuit theory, regardless of how different the intermediate steps may be.  And every trivial change in the DC circuit itself--wire resistance, diameter, length, etc,--does result in a change.

So the result is that the energy is 'flowing' in those fields external to the wire, but there is no possibility of affecting, blocking or intercepting that energy flow no matter what you do in that space.  However, in the wire where the energy is not flowing, any change at all--like hollowing out the wire a bit--does make a difference.  Counterintuitive?   

[SilverSolder]

How would you draw the magnetic lines of force in this example?   I really am struggling to see it.  I'm probably overlooking something obvious.

It would be like a coaxial cable with a very thin dielectric.

So you are saying the thinner we make the insulator, the stronger the magnetic and electric fields will become (to carry the same amount of energy as before)?

[HuronKing]

*Edit*
Others got to this before I could but posting for extra info in case it helps:

The wires are very thin, 0.01mm, just enough to light a small bulb.  The insulation is the thinnest possible layer of vacuum that you can have without flashing over (a few micrometers), and the box is at least 500mm thick.

I am struggling to understand how the fields will be able to carry energy to the bulb.  And if they do make it in...  wouldn't the tortuous path they have to take to get there mean there would be more resistance, compared to a layout that does not impede the fields in any way?

You need to study waveguides. The penetrations cavities through the conductive enclosure with the conducting wire inside the penetration will follow the physics of waveguides... and in essence you've described a penetration that will have characteristics of a coaxial cable.

Long conducting outer shield, very thin internal dielectric, and an inner conductor. The energy is transmitted in the field in the dielectric between the conductors.
https://www.electricalengineeringtoolbox.com/2016/12/basics-of-coaxial-cables-used-in.html

Notice that the velocity of propagation depends chiefly on the insulation you use, the dielectrics:
https://en.wikipedia.org/wiki/Velocity_factor

And the amount of energy stored in these fields depends on the shaping of the conductors and the dielectrics:
https://phys.libretexts.org/Bookshelves/University_Physics/Book%3A_University_Physics_(OpenStax)/Book%3A_University_Physics_II_-_Thermodynamics_Electricity_and_Magnetism_(OpenStax)/14%3A_Inductance/14.04%3A_Energy_in_a_Magnetic_Field

This was Heaviside's great insight into Maxwell's Equations that led him to invent and patent coaxial cables in the first place (I think it was a mistake by Veritasium to show Heaviside's photo and talk about the Transatlantic Cable... and never mention coaxial cables, but I digress).

*Edit2*

Corrected a statement about the velocity propagation and its relationship to the conductivity. This should clarify what I mean:
https://phys.libretexts.org/Bookshelves/Electricity_and_Magnetism/Book%3A_Electromagnetics_II_(Ellingson)/03%3A_Wave_Propagation_in_General_Media/3.11%3A_Good_Conductors

And after all the math analyzing permittivity and conductivities, the key conclusion is:

Thus, the information conveyed by signals propagating along transmission lines travels primarily within the space between the conductors, and not within the conductors. Information cannot travel primarily in the conductors, as this would then result in apparent phase velocity which is orders of magnitude less than  c , as noted previously. Remarkably, classical transmission line theory employing the  R′ ,  G′ ,  C′ ,  L′  equivalent circuit model2 gets this right, even though that approach does not explicitly consider the possibility of guided waves traveling between the conductors.

[SilverSolder]

Let's take a step back, maybe I'm missing the point completely.

Are the fields that carry the energy outside the conductors normal electric and magnetic fields that we can measure if we want to?

[bdunham7]

Let's take a step back, maybe I'm missing the point completely.

Are the fields that carry the energy outside the conductors normal electric and magnetic fields that we can measure if we want to?

Yes.  The 'S-field' vector at any point is the cross product of the E and H field vectors at that point.

[SilverSolder]

Let's take a step back, maybe I'm missing the point completely.

Are the fields that carry the energy outside the conductors normal electric and magnetic fields that we can measure if we want to?

Yes.  The 'S-field' vector at any point is the cross product of the E and H field vectors at that point.

Ah, OK.  So we are really just playing around with cause and effect?   I.e. whether current is the result of the fields, or vice versa.   

The mathematics work out either way...    just like the math works great no matter which direction we believe the current is flowing between plus and minus.   The math can't be used to prove the direction one way or the other...

[SiliconWizard]

The fact it was a chicken-and-egg question was pointed out pages ago. =)

[SiliconWizard]

Energy cannot be created or destroyed, it can only be transformed into another form!

I suppose you are assuming conservation of energy, which holds if we consider an isolated system.
Is the universe an isolated system? I'm not sure this has been fully answered yet. =) But this sure goes beyond the points made in this thread.

Can you think of an example where energy is created or destroyed,  rather than transformed?  -  I have always thought it a very basic law of the known universe...

You might watch this as a quick introduction to the matter:

[rfeecs]

In the steady state, DC, does energy flow in the wires or in the fields?

Start with the fact that energy is contained in electromagnetic waves.  If you have used solar panels, you should believe this is true.

Consider a plane wave propagating through free space.  We know that energy is flowing with the plane wave.  We can measure it, and we can calculate it.  And the energy flux agrees with the Poynting vector.  We don't even need the Poynting vector to calculate it, but it does agree with the calculation:

https://phys.libretexts.org/Bookshelves/University_Physics/Book%3A_University_Physics_(OpenStax)/Book%3A_University_Physics_II_-_Thermodynamics_Electricity_and_Magnetism_(OpenStax)/16%3A_Electromagnetic_Waves/16.04%3A_Energy_Carried_by_Electromagnetic_Waves

Now consider a transmission line.  It can be a twin lead transmission line as we have discussed.  Let's just feed it with a lumped source with say a sine wave.  Again we know energy is propagating.  We can measure it and we can calculate it.  We know the wave fronts are moving and we know that since there is energy in the field, the field is carrying the energy.  We can't say the energy flows in the wires or we would count twice the power that we measure.

Now lets say instead of a sine wave, we just have a battery and a switch.  At time t=0 we turn on the switch.  We have a rising edge, say 0V to 5V.  Now we know that this edge propagates down the line.  We can measure it.  We know that the energy is moving down the line in the fields.  We can see that if we slice up the space into thin slices of width dz, then as the wave front arrives at a point on the line, the energy of the slice goes up, and we know that that energy has to come from the slice behind it.  So one by one slices are filling with energy and energy is flowing all along the line in the fields.

Now if we look at a point where the wavefront has already passed, the fields are constant.  The voltage is constant and the current is constant DC.  But we know that energy is flowing through this point to fill the slices up to the wave front.  So here everything is static, except power is flowing through the fields.

Now we terminate the line with a resistor that matches the impedance of the line.  When the wavefront reaches the resistor it is totally and continually absorbed in the resistor.  But nothing has changed at the previous point on the line we looked at.  Energy is still flowing there in the fields even though the whole system is now in a steady state and DC only.

That's one way of looking at it.

[SilverSolder]

In the steady state, DC, does energy flow in the wires or in the fields?

Start with the fact that energy is contained in electromagnetic waves.  If you have used solar panels, you should believe this is true.

Consider a plane wave propagating through free space.  We know that energy is flowing with the plane wave.  We can measure it, and we can calculate it.  And the energy flux agrees with the Poynting vector.  We don't even need the Poynting vector to calculate it, but it does agree with the calculation:

https://phys.libretexts.org/Bookshelves/University_Physics/Book%3A_University_Physics_(OpenStax)/Book%3A_University_Physics_II_-_Thermodynamics_Electricity_and_Magnetism_(OpenStax)/16%3A_Electromagnetic_Waves/16.04%3A_Energy_Carried_by_Electromagnetic_Waves

Now consider a transmission line.  It can be a twin lead transmission line as we have discussed.  Let's just feed it with a lumped source with say a sine wave.  Again we know energy is propagating.  We can measure it and we can calculate it.  We know the wave fronts are moving and we know that since there is energy in the field, the field is carrying the energy.  We can't say the energy flows in the wires or we would count twice the power that we measure.

Now lets say instead of a sine wave, we just have a battery and a switch.  At time t=0 we turn on the switch.  We have a rising edge, say 0V to 5V.  Now we know that this edge propagates down the line.  We can measure it.  We know that the energy is moving down the line in the fields.  We can see that if we slice up the space into thin slices of width dz, then as the wave front arrives at a point on the line, the energy of the slice goes up, and we know that that energy has to come from the slice behind it.  So one by one slices are filling with energy and energy is flowing all along the line in the fields.

Now if we look at a point where the wavefront has already passed, the fields are constant.  The voltage is constant and the current is constant DC.  But we know that energy is flowing through this point to fill the slices up to the wave front.  So here everything is static, except power is flowing through the fields.

Now we terminate the line with a resistor that matches the impedance of the line.  When the wavefront reaches the resistor it is totally and continually absorbed in the resistor.  But nothing has changed at the previous point on the line we looked at.  Energy is still flowing there in the fields even though the whole system is now in a steady state and DC only.

That's one way of looking at it.

I totally get that with AC, we can transfer energy through the field.  But DC...   hmmm.

There's another Veritasium video that is quite instructive:  how a Slinky spring falls...   Check this out:




First, the fall starts as a wave motion.  Then, once that initial transient is over, the slinky continues as a coherent block of moving particles - a current!

That's another way of looking at DC in a transmission line - a fast wave, followed by a coherent movement of the particles - a current!

[adx]

I have a quick question, maybe someone can help me understand:

What happens if we put the bulb inside a steel Faraday cage?  That would mean an outside electrical field cannot reach it, and any magnetic field would not reach the bulb either (it would by-pass the bulb via the steel box).

If the Veritasium video is right and the energy is carried by the magnetic/electric field and not the wire itself...   wouldn't that mean the bulb would not be able to light up inside the Faraday / magnetic shield cage?  (Similarly, we could put the battery inside a steel box, or both...)

If RF land (not my main skill);

• the highest frequency waves will simply reflect off the box and away.
• Lower frequencies will couple in the wires that remain unshielded. Making the holes (gaps) too small and long will create capacitive feedthroughs which will short out the medium frequencies with a low impedance, reducing the current which flows through to the bulb, and taking it around the Faraday cage, but it will still flow.
• Low and DC frequencies will flow 'through' the cable like normal, by that stage the fields which would otherwise rob the transient of power (to the bulb) are set up and no longer taking energy.

You can still say the energy flows in the fields. Or the cables. If you didn't have holes in the cage and loop, there would be no voltage differences. If you didn't have a hole in space (for the wire etc) there'd be no current.