Does the pointing vector theory hold true for DC current?

[gkangelexa]

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?

 

[SteamKing]

It's called a ground for a reason.

 

[Drakkith]

Current is the flow of charges (in this case Electrons) through the conductor. Like you said the amount of current is the same at the beginning and end of the circuit. The current (charges) never go anywhere, they are always there. Imagine you have a pipe of water with a water pump that pumps it around the pipe in a circle. The water never goes anywhere but around the pipe, but the pump has to perform work on the water to keep it flowing because of resistance.

If you increase the resistance of the pipe then you have less water flowing by a particular point per second than the pipe with less resistance. Similarly, increasing the resistance of the circuit causes less current to flow at all.

It's called a ground for a reason.

Depending on what you mean by ground, that could be mean that it is the return wire for the circuit or that it is the safety wire in a household circuit that only transmits current to ground in a fault situation.

 

[gkangelexa]

So then what do electric companies charge you for? The voltage they provide that is necessary for the current?

 

[Drakkith]

So then what do electric companies charge you for? The voltage they provide that is necessary for the current?

They charge you because it takes work to produce electricity. To produce the voltage that determines the current in a circuit you have to use energy. Typically power plants use fossil fuels or nuclear power to heat water which then turns a steam turbine. The turbine turns a generator which produces the power. The key here is that when the generator is turning there is resistance to it. The more power drawn from the generator the greater the resistance to the generator turning and the more power has to be input to the generator. You are paying for the fuel, infrastructure, employees, ETC.

 

[DaveC426913]

So then what do electric companies charge you for? The voltage they provide that is necessary for the current?

The work done. It does power your lights. Energy is flowing into your house as useful electricity and leaving as waste heat.

 

[pallidin]

Current ... do(es) not increase or decrease or get used up when going through a wire or other device.

Yes it does. That's the whole idea.

 

[russ_watters]

Yes it does. That's the whole idea.

No, it really doesn't. The current at any place in a continuous, brancless circuit is the same.

 

[pallidin]

Uh, no. A resistive device within the circuit will reduce current flow.

 

[BobG]

Drakkith's answer is just about perfect.

Current is the rate of flow.

In this case, the things that are moving (or flowing) are electrons (and the electrical charge associated with those electrons). In an electric circuit, especially if it's AC, those electrons aren't actually going anywhere - they're just moving around in your wires.

You're paying to have those electrons moved for you, not for the electrons. Just like in Drakkith's example, where the water is yours, but you're paying to run the pump that moves the water around for you.

 

[Drakkith]

Uh, no. A resistive device within the circuit will reduce current flow.

Yes, the current throughout the circuit will be reduced, correct?
The current isn't going anywhere or being used up. There is simply less because of the resistance. I think that's what both of you are saying.

 

[pallidin]

Yes, the current throughout the circuit will be reduced, correct?
The current isn't going anywhere or being used up. There is simply less because of the resistance. I think that's what both of you are saying.

Well, it IS being used up, in a sense. It HAS to be, else one would have perpetual motion with infinite energy draw.
The key is "conversion" A specific amount of current flow is reduced, by conversion, to, say, heat or light. Thus there IS less current.

 

[phinds]

Well, it IS being used up, in a sense. It HAS to be, else one would have perpetual motion with infinite energy draw.
The key is "conversion" A specific amount of current flow is reduced, by conversion, to, say, heat or light. Thus there IS less current.

No, the heat or light is produced by the work done at the power station in moving the electrons around the circuit loop. To get more current to produce a brighter light, the power station has to do more work. The current isn't used up at all. What's used is the work being done at the power station. That's what you are paying for (well, that and all those wires that the power company has to maintain).

 

[pallidin]

I would confidently say that my 1500 watt electrical space heater is, in fact, initially reducing current at IT'S LOCATION, not the power station.
The "power station" must then ramp-up current flow to compensate for the losses at my space heater's location.
Thus the "bill"

 

[Naty1]

current is loosly bound electrons moving along from atom to atom in a conductor...they don't "disappear...

Perhaps what you are thinking about is energy (power)...THAT is what is being consumed by electrical appliances...electrons don't disappear in loads anymore than they are produced at generating devices.

palladin: try reading about Kirchoff's current law.

 

[DrGreg]

I would confidently say that my 1500 watt electrical space heater is, in fact, initially reducing current at IT'S LOCATION, not the power station.
The "power station" must then ramp-up current flow to compensate for the losses at my space heater's location.
Thus the "bill"

When your heater is switched off, there's zero current through it, so when it's switched on it's increasing the current, not reducing it. But it does cause a small drop in voltage, which the power station has to compensate for.

 

[pallidin]

current is loosly bound electrons moving along from atom to atom in a conductor...they don't "disappear...

Perhaps what you are thinking about is energy (power)...THAT is what is being consumed by electrical appliances...electrons don't disappear in loads anymore than they are produced at generating devices.

palladin: try reading about Kirchoff's current law.

I never said or suggested that the actual electrons are "consumed"
Rather, what I am saying is that the energy during the event most cetainly is(rather converted) to heat, light, etc...
That event requires a reduction in current flow.

 

[Naty1]

That event requires a reduction in current flow.

no.

where do you think the electrons go??

you have energy and current confused.

 

[pallidin]

When your heater is switched off, there's zero current through it, so when it's switched on it's increasing the current, not reducing it. But it does cause a small drop in voltage, which the power station has to compensate for.

Look, it's very simple: Resistive devices in an electrical circuit DISSIPATE energy.
This action necessarily results in a quantifiable reduction in current flow.

 

[pallidin]

OK, everyone. A reduction in electron "flow" DOES NOT in any way mean a loss of the specific electrons themselves...

 

[DrGreg]

Look, it's very simple: Resistive devices in an electrical circuit DISSIPATE energy.
This action necessarily results in a quantifiable reduction in current flow.

When you talk about a reduction of current, please specify precisely which two currents are being compared.

 

[phinds]

I would confidently say that my 1500 watt electrical space heater is, in fact, initially reducing current at IT'S LOCATION, not the power station.

Then I would confidently say that you should study electricity more.

 

[pallidin]

Then I would confidently say that you should study electricity more.

I must respectfully say that, IMHO, you are wrong. Love you and cheers :)

 

[russ_watters]

Pallidin, you need to learn the definitions of the words you are using. "Current" is a flow rate of charge -the number of electrons flowing past a point in a circuit. It is NOT synonymous with energy or power.

If the flow rate of electrons were different in different parts of a circuit, they would have to disappear or be created. Just like the flow rate of water through a pipe.

 

[phinds]

I must respectfully say that, IMHO, you are wrong. Love you and cheers :)

Pallidin,

I completely get that you are not being rude and I take no offense at your disagreement. As Russ said, you seem to be confused about the terms being used. I haven't opened any of my Electrical Engineering textbooks in over 40 years, but I don't really need to look this one up to know what's right.

Your opinion (and mine as well for that matter) are irrelevant to the situation. Facts are facts and electricity is a well understood phenomenon at the macro level we are talking about.

The only way you can push any amount of current out one end of a power line is to get the same amount of current back in the other end of the line. What it does in between can cause the voltage across the line to drop if the power being supplied is insufficient to drive the voltage*current power load but the only way for the current to be reduced at the load is for the power station to drive out (and get back) less current.

 

[sophiecentaur]

I would confidently say that my 1500 watt electrical space heater is, in fact, initially reducing current at IT'S LOCATION, not the power station.
The "power station" must then ramp-up current flow to compensate for the losses at my space heater's location.
Thus the "bill"

You should really bone up on this before you "confidently say" something. Learn what Current Volts, Power and all the other quantities are.

Would you say that there are a different number of links in your bicycle chain entering your rear wheel sprocket than links entering your chain wheel sprocket when you are powering up hill? 'Cos that's as wrong as what you are implying about current flow.

 

[phinds]

Would you say that there are a different number of links in your bicycle chain entering your rear wheel sprocket than links entering your chain wheel sprocket when you are powering up hill? 'Cos that's as wrong what you are implying about current flow.

Excellent analogy, nicely put.

 

[pallidin]

Excellent analogy, nicely put.

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

 

[DrGreg]

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

So we're supposed to read your mind to find out why you think a good analogy is bad?

 

[Drakkith]

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

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.

 

[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?