Does the pointing vector theory hold true for DC current?

[phinds]

Not so fast... that a REALLY bad analogy.
I'll leave it to you to understand why.

I'm confident that I DO understand ... why it is a good analogy. Your concept about current is just mistaken.

 

[sophiecentaur]

Not so fast... that a REALLY bad analogy.
I'll leave it to you to understand why.

Sorry. That's not enough. If you can't justify what you say, the statement has no worth.
(leaps to own defence) :-)

 

[sophiecentaur]

It seems perfectly fine for an analogy to me. After all, it's just an analogy. The force you apply to the pedals is the voltage, the chain is the current, the resistance is the hill. Seems perfectly fine to me. It ain't perfect, but it works.

It even has the potential difference across source and load there, because the tension over the top is greater than along the bottom section of chain. The tension in the chain will stretch it a finite amount - so each link carries some strain energy with it (aka each C carries V Joules with it) and it is the difference in tension, before and after, that tells you how much Power is transferred per link. You can even have driven sprockets in series around the chain and the tensions (PDs) add up as you go round, Giving you K2, even.
Palladin is going to have to try pretty hard, I think.

 

[phinds]

Palladin,

You continue, in the face of considerable opposition, to promote a view of electric current that is inconsistent with physics as the rest of us understand it. You have been given definitions of the fundamental terms that you seem to be confusing, you have been referred to Kirchoff's current law, you have been asked a question ("... please specify precisely which two currents are being compared") which you have not answered and yet you continue to simply state without any justification what the rest of us see as an unjustifiable position, because it is what you BELIEVE, not because it is what you can support with facts. You have offered no facts. You have not attempted to refute Krichoff (good luck with that by the way). You seem to have ignored much of what others here have said in an attempt to clarify the phenomenon.

I see from your number of posts that you are not new here, so surely you can see how your actions apprear similar to those of crackpots who simply promote a threory with no justification. Please in future posts on this thread support your argument with something more concrete than just your opinion and then perhaps we can engage in a meaningful discussion instead of just arguing past each other.

 

[DaveC426913]

Pallidin may not be right but the best way to put a nail in the coffin of his claims is for some expert to simply state what is happening.

So: When electricity in a circuit is converted to another form, (say light in a lightbulb) what "happens" to the energy in the circuit?

OK, there is no reduction in current. Is there a reduction in voltage?

What is the net difference between a circuit containing a light that's off and an identical circuit with a light that's on?

 

[sophiecentaur]

Pallidin may not be right but the best way to put a nail in the coffin of his claims is for some expert to simply state what is happening.

So: When electricity in a circuit is converted to another form, (say light in a lightbulb) what "happens" to the energy in the circuit?

OK, there is no reduction in current. Is there a reduction in voltage?

What is the net difference between a circuit containing a light that's off and an identical circuit with a light that's on?

Easy. You can see one but you can't see the other. Boom boom.

 

[DaveC426913]

Easy. You can see one but you can't see the other. Boom boom.

That is one difference, but it is not the only difference.

 

[cepheid]

I think part of the problem is as follows: we know that the electrons impart energy to e.g. atomic nuclei in the crystal lattice of whatever conductor they're in. This leads palladin to conclude that the electrons must be losing kinetic energy and hence slowing down. That would seem to necessarily imply a reduction in "current" as we are all defining it.*

So what's wrong with this picture? To my knowledge, the issue is perhaps that a macroscopic and steady state view of things is insufficient. The only microscopic picture I recall is a really crude classical model (the name of which escapes me atm). In this model, electrons zip around in all random directions at speeds characteristic of their temperature (I estimate ~ 10^5 m/s at room temp ?!). They are constantly colliding with atomic nuclei and changing direction (with the rate of collisions depending on the resistivity of the material). With no externally applied electric field, there would no net flow of electrons in any direction. But with an external field, there is a much much much slower and roughly constant net flow of electrons in the direction opposite the applied field. (It's much slower because of the inefficiency of having to bounce around all the time -- the field barely gets a chance to accelerate the electron before it collides again). The roughly constant speed of net flow is called the drift velocity, and I seem to recall it is of order cm/s (or something ridiculously slow like that).*

It is entirely possible that, as electrons lose kinetic energy due to collisions, the speeds associated with their random thermal motions are reduced, with no noticeable effect on the drift velocity (which was so much smaller anyway). Plus we mustn't forget electron-electron interactions. Let's say the drift velocity was reduced at some point in the circuit. That would cause a local "pile-up" of charge there that would in turn create an electric field that would then smooth out the charge distribution. So basically the mutual repulsion of electrons smooths things out and keeps the flow steady.*

Comments?

Edit: and I'm sure it must be possible to use this model to explain Ohm's law, which we're all falling back on when attempting to explain to palladin why he/she is mistaken.

 

[pallidin]

Hopefully not in opposition of PF rules, I do like posing "devil advocate" comments to more thoroughly understand an OP's question/position as well as, more importantly, incite expert response.
I have done this a number of times, and have found it quite useful in "zero-response" questions.
I apologize to all if this has been inappropriate.

 

[DaveC426913]

Hopefully not in opposition of PF rules, I do like posing "devil advocate" comments to more thoroughly understand an OP's question/position as well as, more importantly, incite expert response.
I have done this a number of times, and have found it quite useful in "zero-response" questions.
I apologize to all if this has been inappropriate.

I must grant that, if having the right answer was not necessarily what you accomplished, at least demonstrating that no one else seems to have a much better answer is something you certainly seem to be accomplishing.

You could claim success of a sorts, by way of "no contest".

 

[Fun Value]

I'm back to stick my edit right here in the beginning. When I replied to the original question I read all the posts that I saw. At that time I thought there was only one page of very few replies. I looked for other pages and didn't see any. So I posted the following which is my best guess. I might get some helpful corrections to what I assumed I already understood.
Here is what my reply was. The electrical device is like a waterfall. At the top of the waterfall is the positive side of the battery or battery eliminator and the bottom is like the negative side. The positive side of the outlet is like the top of the water fall. The negative side is like the bottom of the waterfall. The pool at the bottom of the waterfall is like the negative side of the electrical device and like the negative terminal of the battery or battery eliminator.

 

[AtomicJoe]

Current and charge do not increase or decrease or get used up when going through a wire or other device. The amount of charge that goes in at one end comes out at the other end.

Where does the current go then, when I run electrical devices? If it is not used up when I turn on a light bulb or use the TV, where does it go?

it does not go anywhere, the current in your house is alternating current so it just goes forward a bit and then back.

I am not sure of the exact distance but it is not far, I found a example for a 100watt bulb and it moves at 80mm an hour, thus for a bulb at 50 herts it moves a really tiny distance.

You are talking about in the region of 1/1000 of a millimetre or something like that (you do the maths), so basically all your current stays in your mouse.
calc = 80/ 60 x 60 x 50 = 80/ 180000 = 1/2250 of a millimetre, ie not very far!

 

[Per Oni]

The electrical device is like a waterfall. At the top of the waterfall is the positive side of the battery or battery eliminator and the bottom is like the negative side. The positive side of the outlet is like the top of the water fall. The negative side is like the bottom of the waterfall. The pool at the bottom of the waterfall is like the negative side of the electrical device and like the negative terminal of the battery or battery eliminator.

To compare an electric field across a conductor with a gravitational field of a waterfall is not bad at all. In this case you can compare falling water with electrons, with the exception that electrons will not continuously accelerate but rather have a terminal velocity like raindrops falling through the air. This terminal velocity is due to factors like the ones mentioned in post #38.
Just like one raindrop is not actually pushing the next one, likewise an electrical current is not “the first electron pushing the next one and so on and on”. This “pushing theory” is similar to the garden water hose analogy and the “pulling theory” is the bicycle chain theory and both are wrong.

Boom boom (Doing a pallidin, its catching).

 

[Drakkith]

How can the electrons not be pushing other electrons? How else would the emf or voltage or whatever move down the line?

 

[Antiphon]

All current begins in the Yin, loses energy to the Chi (or is it the Tao?), and flows into the Yang.

Sorry, I couldn't resist.

The actual movement of charges in a wire is very slow as has been pointed out. For AC power distribution at 60 Hz, essentially the charges go nowhere. If you plug in you alarm clock now, ten years from now the same electrons will probably reside in the plug.

The energy is not transmitted by the electrons pushing up against one another. It is transmitted through the fields (E, H) in the air around the wires and can be calculated via the Poynting vector which is zero in the wire but not in the space around it.

The reason charges don't bunch up is exactly because they do repel one another. Anyplace they did bunch up would be at a higher voltage. This can only happen between conductors which are insulated from one another. In a typical circuit there is non-zero resistance all the way around which keeps charge from bunching up but does exhibit voltage drops.

 

[Drakkith]

The actual movement of charges in a wire is very slow as has been pointed out. For AC power distribution at 60 Hz, essentially the charges go nowhere. If you plug in you alarm clock now, ten years from now the same electrons will probably reside in the plug.

The energy is not transmitted by the electrons pushing up against one another. It is transmitted through the fields (E, H) in the air around the wires and can be calculated via the Poynting vector which is zero in the wire but not in the space around it.

This doesn't make any sense to me. The force doesn't just magically get into the air and wire, it has to have charges carry it. If you apply a potential to the conductor on one end, it influences the electrons so that the average movement is in net direction. Each electron only has to move a very very small distance, but the voltage or emf or whatever travels down the conductor very quickly.

 

[Antiphon]

This doesn't make any sense to me. The force doesn't just magically get into the air and wire, it has to have charges carry it. If you apply a potential to the conductor on one end, it influences the electrons so that the average movement is in net direction. Each electron only has to move a very very small distance, but the voltage or emf or whatever travels down the conductor very quickly.

Does a microwave heating your food make sense? How about the sun warming your hand? No wires.

The wires are only there to guide the fields to where you want them to be. The force is in the air, just not magically, rather Maxwell-ly.

 

[ZealScience]

Current is never used, because charge is conserved. And there is not accummulation of charge in the appliance (have you ever seen appliance is charged?). So the current is flow in in complete circuit from beginning to the end.

The thing being used up is not charge, but energy. There is certain electric field change in the appliance that consumes/stores (capacitor) potential energy.

 

[berkeman]

Hopefully not in opposition of PF rules, I do like posing "devil advocate" comments to more thoroughly understand an OP's question/position as well as, more importantly, incite expert response.
I have done this a number of times, and have found it quite useful in "zero-response" questions.
I apologize to all if this has been inappropriate.

If you are going to play the devil's advocate role in a post, and it is not very obvious by the context, please state as much in your reply. Please check your PMs.

 

[Drakkith]

Does a microwave heating your food make sense? How about the sun warming your hand? No wires.

The wires are only there to guide the fields to where you want them to be. The force is in the air, just not magically, rather Maxwell-ly.

What? I wasn't referring to photons, I was talking about the emf through a conductor. Can you point to anything incorrect in my post or not?

 

[Antiphon]

What? I wasn't referring to photons, I was talking about the emf through a conductor. Can you point to anything incorrect in my post or not?

Not referring to photons? What do you think the power plant is sending into your house? It's photons.

This doesn't make any sense to me. The force doesn't just magically get into the air and wire, it has to have charges carry it.

This is incorrect. See the sunlight.

If you apply a potential to the conductor on one end, it influences the electrons so that the average movement is in net direction. Each electron only has to move a very very small distance, but the voltage or emf or whatever travels down the conductor very quickly.

This is correct but it's missing the true mechanism of power flowing. The flow of power down a pair of wires is not even a little bit analogous to sound or pressure in a pipe.

Simplest example: perfectly conducting wires. There's no component of the electric field aligned along the wire. It's totally perpendicular to the wire. The power flow is given by the integral of \vec{E} X \vec{H} over a closed surface. If you integrate this in the wires it's zero. If you integrate in the air around the wires it's the power flowing down the line.

Repeat: the energy flowing down a pair of wires travels in the space between the wires as photons and not in the wires as charge x field x distance.

 

[berkeman]

Thread closed overnight...

Okay, re-opening the thread for now. Please keep the discussion civil and technically accurate.

For AC power transmission where the dimensions of the transmission line are comparable to a wavelength, then yes, the power is largely transmitted as an EM wave.

But for DC power transmission, or low-frequency AC transmission (where the distribution system's size is much less than a wavelength), then the power is not being transmitted by "photons".

 

[Per Oni]

How can the electrons not be pushing other electrons? How else would the emf or voltage or whatever move down the line?

Hey folks, those of you who think electrical power is transported by electrons through a wire analogous to water in a water hose, please consider the following:
We know the drift speed of conducting electrons is very low. Say Vd=10^-3 (in fact it’s even a little below this value). Say I want to drive a motor of a modest 1KW dc with 1Amp. Please work out first of all the force required in the connecting cable to be able to develop such a power with this velocity. (A touch high?)
Next look up what size cable is needed for a 1 amp current . In this case, for copper wire the current density can be ~ 10^7 /M^2. From calculated force and wire surface area, a pressure can be calculated. ( A bit steep?)
This example is by no means extreme. Please use instead real existing values for a 100W light bulb in your own home. DO IT!

 

[Evil Bunny]

Where does the current go then, when I run electrical devices? If it is not used up when I turn on a light bulb or use the TV, where does it go?

It goes back to the source. It leaves one side of the source, and the same amount returns on the other side of the source. This never changes...

It's called a ground for a reason.

Incorrect. It does not flow into the ground. It only flows back to the source.

So then what do electric companies charge you for?

You're paying for the energy it took to move the electrons from one side to the other. Back at the generator, some sort of prime mover did work to move the electrons through all your appliances. You pay for that. EDIT: And you pay for the infrastructure to get it from the generator to your house, of course...

 

[russ_watters]

Hey folks, those of you who think electrical power is transported by electrons through a wire analogous to water in a water hose, please consider the following:
We know the drift speed of conducting electrons is very low. Say Vd=10^-3 (in fact it’s even a little below this value). Say I want to drive a motor of a modest 1KW dc with 1Amp. Please work out first of all the force required in the connecting cable to be able to develop such a power with this velocity. (A touch high?)
Next look up what size cable is needed for a 1 amp current . In this case, for copper wire the current density can be ~ 10^7 /M^2. From calculated force and wire surface area, a pressure can be calculated. ( A bit steep?)
This example is by no means extreme. Please use instead real existing values for a 100W light bulb in your own home. DO IT!

What are you trying to say? Are you suggesting that electrical power is really mechanical power like water? That's not at all intended to be implied by the analogy. It's an analogy.

 

[Drakkith]

Hey folks, those of you who think electrical power is transported by electrons through a wire analogous to water in a water hose, please consider the following:

As Russ said, it isn't the same. The electrical force is pushing electrons down the entire conductor. And in reality, the force is pushing the electrons, but it is attracting the protons in the conductor. Since the protons are not mobile they cannot move, and the electrons move by themselves. The key here is that it is the FORCE that causes the electrons to move. Everything about "energy" or "power" flowing here and there and all that is irrelevant and misleading, and a look at the definitions of both will immediately tell you that. This whole thread is about current, the movement of charges. How much work has been performed, or where the energy came from doesn't matter.

 

[Antiphon]

The Poynitng vector definition of power flow is the only one well-defined here. Berkeman, it applies to the DC case as well.

See paragraphs 1-8, speficially 8 for a description of how to carry out the integration.
http://personal.ee.surrey.ac.uk/Personal/D.Jefferies/poynting.html

Yes, the thread was about current. But the topic of power came up because of the false notion that (in a DC case even) current flow happens by the electrons pushing on one another. But this is not correct.

In the steady state DC case of zero resistance there is zero electric field vector in along the wire inside and out. Drak, there simply is no electric force pushing current down the wire. The current, once established, moves under it's own momentum (contained NOT in the electron mass but in the magnetic field.)

The ONLY way to mathematically compute the power flow is via the fields in the space around the wire. It is extremely suspect to claim that the power is confined to the wires where there is only a static magnetic field at best and zero electric field.

 

[Per Oni]

What are you trying to say? Are you suggesting that electrical power is really mechanical power like water? That's not at all intended to be implied by the analogy. It's an analogy.

Ok we both now that electrical power is not like water through a hose.

My point is however that you and others (using this analogy) want to transport power down a wire. According to you, this power is transported via electrons flowing through a fairly thin conductor in such a way that one electron pushes the proceeding one and gets pushed by the one behind.

I just want to stop here and see whether this is your point of view.

(I am sorry that I cannot respond quickly but mostly have a short time in the UK evening for posts).

 

[Drakkith]

Drak, there simply is no electric force pushing current down the wire. The current, once established, moves under it's own momentum (contained NOT in the electron mass but in the magnetic field.)

I have been looking up this phenomena due to this thread and another. I'll have to get back to you.

 

[Per Oni]

In conclusion:

Just some points to explain why I’m so opposed to the fairly innocent notion of the “water hose / bicycle chain” analogy. My reason is that it only perpetuates the idea that energy/power to a load flows through a wire. That really is a ridiculous notion as I have shown. Mind however that some of the very biggest names have slipped up on this one.

There really is no alternative to this problem then using the theory as set out by the likes of Antiphon. To me this theory makes sense in an actual physical way but also mathematically. Now, there are not many good web sites or books I can refer to, just because strangely enough it’s still a controversial idea. I’m also not 100% convinced of all the points that Antiphon has raised, such as the photons and momentum but no doubt science will crack those points eventually.