Speaker wires don't carry any energy (power).

[tomtoo]

I think I've got it figured out. Tiny little people called electrichauns run along the wire to the bulb carrying packets of electricity which the bulb gobbles up. They then run back to the battery along the other wire picking up another packet and so on. The brightness of the bulb depends on how fast they run. When their shift is over the electrichauns, being of Irish descent, relax by imbibing a substance called quanteen. This frequently results in the electrichauns becoming either paralytic or even starting fighting and ending up in the emergency department of the local hospital. At such times your electrical apparatus may suddenly stop working for no apparent reason. Sometimes if you thump the errant apparatus it will jolt the little buggers back to consciousness and it will start working again. Let that be an end to the matter.

Yes and sometimes they consume so much quanteen, that they not even find the line anymore and spread in every direction, thats called HF. Higly full.

 

[jeroboam]

I infer from this that you haven't studied much thermodynamics and/or read much Thomas Pynchon.

Guilty as charged

 

[Cbdb2]

That was not my point ;-)

Anyway: "Since the wire has resistance, there is an electric field along it, driving the current. Because there is a potential drop along the wire, there is also an electric field just outside the wire, parallel to the surface. (See Fig. 27–5.) There is, in addition, a magnetic field which goes around the wire because of the current. The E and B are at right angles; therefore there is a Poynting vector directed radially inward, as shown in the figure."

The picture clearly shows the two parallel E fields, both at right angles with respect to the B field that, in its turn, is tangent to the wire surface. Hence the Poynting vector points towards the center of the conductor ("radially inward"), not "slightly".

The Poynting vector shows the direction of energy flow. Your saying all the energy goes into the wire and non is transfered to the load. The picture shows what happens in a resistor (or a wire with resistance). " Because there is a potential drop along the wire, there is also an electric field just outside the wire, parallel to the surface." And from Wilkipedia "If a conductor has significant resistance, then, near the surface of that conductor, the Poynting vector would be tilted toward and impinge upon the conductor. Once the Poynting vector enters the conductor, it is bent to a direction that is almost perpendicular to the surface. "

And "For example, the Poynting vector within the dielectric insulator of a coaxial cable is nearly parallel to the wire axis (assuming no fields outside the cable) - so electric energy is flowing through the dielectric between the conductors. If the core conductor was replaced by a wire having significant resistance, then the Poynting vector would become tilted toward that wire, indicating that energy flows from the e/m field into the wire, producing resistive Joule heating in the wire." From"https://www.chemeurope.com/en/encyclopedia/Poynting_vector.html"

Dosnt matter if its DC or AC if there's energy transfered theres a Poyting vector in the direction of the energy flow.

 

[giuppo77]

The Poynting vector shows the direction of energy flow. Your saying all the energy goes into the wire and non is transfered to the load. The picture shows what happens in a resistor (or a wire with resistance). " Because there is a potential drop along the wire, there is also an electric field just outside the wire, parallel to the surface." And from Wilkipedia "If a conductor has significant resistance, then, near the surface of that conductor, the Poynting vector would be tilted toward and impinge upon the conductor. Once the Poynting vector enters the conductor, it is bent to a direction that is almost perpendicular to the surface. "

I am not (and I do not want to) saying anything. I have just reported what Feynman says in its famous lectures in Physics. If you think that what Feynman said is not correct or/and that wikipedia is more correct, then fine with me.

My intention was to focus on what Feynman was saying in general about the Poyinting vector (and I have reported the related sentences). I have found that very brilliant and wanted to share with you that idea. Nothing more, nothing less.

 

[audio2design]

I am not (and I do not want to) saying anything. I have just reported what Feynman says in its famous lectures in Physics. If you think that what Feynman said is not correct or/and that wikipedia is more correct, then fine with me.

My intention was to focus on what Feynman was saying in general about the Poyinting vector (and I have reported the related sentences). I have found that very brilliant and wanted to share with you that idea. Nothing more, nothing less.

I don't think @Cbdb2 is disagreeing with Feynman.

What I am perceiving is a misunderstanding of the Poynting vector. It is a cross-product of the E&B fields, calculated at a point is space, or perhaps integrated over a space if one so desires. So close to a source it will point out from the source, but not necessarily towards the load at that point in space, and it will point in towards a load if the point is close to the load, etc. When we say the Poynting vector points from source to load, we mean if we take a cut in space between the two and integrate the cross product. Localize direction will be different.

 

[Astrozombie]

Freakin spoilers man i have the video bookmarked but haven't seen it .

 

[xaviescacs]

I said I have left the thread but I want to add something. Guys, the Poynting vector is very nice, but it's not a real thing. The cable, the particles, the light, those are real things, facts that exist regardless of ourselves. The Poynting vector it's not. The fact that the Poynting vector points one direction or another gives some information as it models how the energy travels, of course, and gives us some notion about how EM describes this situation, and therefore the discussion of its nature is of great relevance. But that can't leads us to say the energy goes outside the conductor. The energy, as I've said before, goes from one electron to the other inside the conductor. The energy is one electron excited, in a quantum state with greater energy than its rest state. This is why it's fundamentally wrong what the video says about where the energy is. I needed to say that. Keep up!

 

[audio2design]

I said I have left the thread but I want to add something. Guys, the Poynting vector is very nice, but it's not a real thing. The cable, the particles, the light, those are real things, facts that exist regardless of ourselves. The Poynting vector it's not. The fact that the Poynting vector points one direction or another gives some information as it models how the energy travels, of course, and gives us some notion about how EM describes this situation, and therefore the discussion of its nature is of great relevance. But that can't leads us to say the energy goes outside the conductor. The energy, as I've said before, goes from one electron to the other inside the conductor. The energy is one electron excited, in a quantum state with greater energy than its rest state. This is why it's fundamentally wrong what the video says about where the energy is. I needed to say that. Keep up!

Are you saying that electrons are emitting photons going from the higher quantum state to the lower state in the conductor?

When will you explain transformers and capacitors to us? .... why does an inductor with the same level of current as a wire store energy, but the wire does not or at least not much?

 

[mansr]

Are you saying that electrons are emitting photons going from the higher quantum state to the lower state?

If that "lamp" is an LED, sure.

 

[xaviescacs]

Are you saying that electrons are emitting photons going from the higher quantum state to the lower state in the conductor?

All I'm saying is that model are there to help us understand what's going on, not to drive our knowledge.

A photon is a quanta of energy, that is, some amount of energy being transferred from one particle to the other. Don't imagine photons traveling freely through the conductor. This is why the speed of light is a bit slower than in void. And this is also why I used the analogy with waves in water. The energy it's being transferred from one place to another because the water is going up and down, storing and releasing potential energy, and passing it to the next "bunch" of water by means of forces, as in a rope.

When will you explain transformers and capacitors to us? .... why does an inductor with the same level of current as a wire store energy, but the wire does not or at least not much?

What do you mean by "store energy"?

I believe you know how transformers work, one current induces energy to the other conductor. That is, the excitement of electrons in one conductor induces excitement in the electrons of the other conductor, because when electrons move due to Lorentz force, they create fields, radiate, etc. etc. And this process is described very well by EM, because its predictions are quite accurate. In transformers, we use other metals to drive the energy to the place we want, namely a transformer core, and we can achieve a minimum loss of energy, because we are able to "drive" the photons the way we want.

There is no model that can explain everything analytical, I'm just saying that we must not loose the notion that no model contains all truth, each one contains some degree of truth and combining them is our best chance to understand what's going on.

Edit: to complement this, I must add that the particles that carry the EM interaction are the W and Z bosons.

 

[samsa]

I said I have left the thread but I want to add something. Guys, the Poynting vector is very nice, but it's not a real thing. The cable, the particles, the light, those are real things, facts that exist regardless of ourselves. The Poynting vector it's not. The fact that the Poynting vector points one direction or another gives some information as it models how the energy travels, of course, and gives us some notion about how EM describes this situation, and therefore the discussion of its nature is of great relevance. But that can't leads us to say the energy goes outside the conductor. The energy, as I've said before, goes from one electron to the other inside the conductor. The energy is one electron excited, in a quantum state with greater energy than its rest state. This is why it's fundamentally wrong what the video says about where the energy is. I needed to say that. Keep up!

I'm sorry. But that's nonsense. The energy carried by the electromagnetic field is a real thing. It's how the sun warms the earth, it's how radios work, it's ...

You can mumble about quantum this and quantum that, but in the situation at hand, quantum mechanical effects are completely irrelevant. Classical E&M is a perfectly fine description.

The video is wrong, but not for the silly reason you say.

It doesn't matter what the Poynting vector is. Shine a bright light on the circuit, and the Poynting flux is huge. But that doesn't make the bulb light up. What matters (all that matters) is that there's an electric field gradient across the terminals of the light bulb, that causes a current through the bulb.

Shortly after the switch is closed, there is such a gradient (it's tiny, but it's nonzero). But, as the charge flows down the wire, the leading edge of the charge distribution recedes (at nearly the speed of light), and the electric field gradient across the terminals of the light bulb drops to zero again. 1 second later, the leading edge of the charge distribution flowing through the return wire reaches the lightbulb and, again, we have an electric field gradient across the terminals of the bulb.

 

[xaviescacs]

I'm sorry. But that's nonsense. The energy carried by the electromagnetic field is a real thing. It's how the sun warms the earth, it's how radios work, it's ...

You can mumble about quantum this and quantum that, but in the situation at hand, quantum mechanical effects are completely irrelevant. Classical E&M is a perfectly fine description.

Don't be sorry.

The energy is a real thing of course, not the Poynting vector, which is a model.

The energy traveling from the sun is made of quanta of energy, photons, traveling through space and reaching the earth. We can describe them as EM waves too, and then we can use Maxwell equations.

These are no quantum mechanics effects, this is particles, the constituents of everything, what is going on there. EM is a model above this, but the underlying reality are particles that travel, interact, emit, absorb, etc. Maxwell equations are fine because they allow us to understand and predict a lot of things that cant be solved analytically using quantum mechanics and particle physics. But that doesn't change the reality of things: everything is made of particles that interact with each others.

There is no contradiction here, just different ways of understanding nature. Can you explain with Maxwell equations why this energy comming from the sun heats earth? You need something else to explain this. And that is because although photons can be regarded as EM waves, this model does not explain everything they do.

 

[samsa]

Don't be sorry.

The energy is a real thing of course, not the Poynting vector, which is a model.

The energy traveling from the sun is made of quanta of energy, photons, traveling through space and reaching the earth. We can describe them as EM waves too, and then we can use Maxwell equations.

And, when you do, the energy carried by the electromagnetic field is given by the electromagnetic energy-momentum tensor, whose "0-i" component is the Poynting vector.

These are no quantum mechanics effects, this is particles, the constituents of everything, what is going on there. EM is a model above this, but the underlying reality are particles that travel, interact, emit, absorb, etc. Maxwell equations are fine because they allow us to understand and predict a lot of things that cant be solved analytically using quantum mechanics and particle physics. But that doesn't change the reality of things: everything is made of particles that interact with each others.

There is no contradiction here, just different ways of understanding nature. Can you explain with Maxwell equations why this energy comming from the sun heats earth? You need something else to explain this. And that is because although photons can be regarded as EM waves, this model does not explain everything they do.

Classical physics does not explain everything. There are situations where it does not apply. This is not one of those situations. Saying that the world is "really quantum-mechanical" (and that one can't understand what's going on here without it) is, in this context, mere obfuscation (very much like the obfuscation in the video).

 

[xaviescacs]

Classical physics does not explain everything. There are situations where it does not apply. This is not one of those situations. Saying that the world is "really quantum-mechanical" (and that one can't understand what's going on here without it) is, in this context, mere obfuscation (very much like the obfuscation in the video).

As you said, and I agree, EM is enough to explain what going on in this experiment. Furthermore, no one is able to solve analytically what is going on here using particles physics. Therefore, Maxwell equations are the best we have to describe and understand what is going on here.

However, one can not forget that what is really there is particles interacting with each other, and therefore one must be aware of the limitations of EM model. If EM model tells you that the energy is traveling around the conductor and not inside the conductor, you must handle this assertion with care and interpret it within this framework.

 

[Andrew s]

But that doesn't change the reality of things: everything is made of particles that interact with each others.

In QED/QCD everything is described by quantum fields and there excitations. For the EM field there are some situations where a particle perspective of the excitations works but they are limited special cases not at all the norm.
Regards Andrew

 

[xaviescacs]

Saying that the world is "really quantum-mechanical" (and that one can't understand what's going on here without it) is, in this context, mere obfuscation (very much like the obfuscation in the video).

World is made of particles, and their interactions and behavior are explained with standard model and quantum mechanics. This is how it goes. We have other models, older models, that explain a lot of things and allow us to build machines without caring about particles, the same as we can walk on the park without caring about EM nor particles.

Really, I'm not trying to deny anything, just opening the scope a bit.

 

[samsa]

As you said, and I agree, EM is enough to explain what going on in this experiment. Furthermore, no one is able to solve analytically what is going on here using particles physics.

No one tries to explain the fluctuations of the Stock Market by solving particle physics equations either. Both would be a stupid waste of time.

Therefore, Maxwell equations are the best we have to describe and understand what is going on here.

Correct.

However, one can not forget that what is really there is particles interacting with each other, and therefore one must be aware of the limitations of EM model. If EM model tells you that the energy is traveling around the conductor and not inside the conductor, you must handle this assertion with care and interpret it within this framework.

If classical E&M is a valid description of situation at hand, then the answers it gives are valid too. If you find those answers unintuitive, I can assure you that quantum effects (in those situations where they are relevant) are way more unintuitive.

 

[xaviescacs]

If you find those answers unintuitive, I can assure you that quantum effects (in those situations where they are relevant) are way more unintuitive.

Do you find quantum mechanics unintuitive? I've done so many hours of it that I feel like home there, but that's a very personal matter.

 

[samsa]

Do you find quantum mechanics unintuitive? I've done so many hours of it that I feel like home there, but that's a very personal matter.

If you find classical E&M unintuitive, then QED is not going to help you.

 

[xaviescacs]

If you find classical E&M unintuitive

Have I said that? I only said it can't explain everything and has its limitations.