Conceptual understanding of generating electricity

[pinchharmonic]

Hi,

Originally I had a question about a wire that allows electrons to move to higher voltage. I could not figure out why the wire does not lose electrons to the point it runs out.

The question was answered on these forums when someone mentioned salt bridges, which lead me to watch some video on how a battery works and electrons are removed from zinc atoms through the wire to end up in some copper solution. Then some sulfate ions are passed between the two sides to maintain some potential difference. That explained where the electrons were coming from (the metal plate and the solution), which could run out.

But then I was looking at a video on turbines and simple methods of generating electricity by spinning a coil of wire in a magnetic field. I do understand from my limited physics knowledge of right-hand-rule that a current will generate as that coil spins, but where are the electrons coming from? Wouldn't you run out of electrons?

But I guess that is under the assumption that the generator is producing a current of electrons to the grid.

I guess if it was the other direction, where electrons are actually coming from the grid->the coil it would make more sense, but if that was the case, then the electrons just float off of the wire into the space where the generator is?

 

[russ_watters]

But then I was looking at a video on turbines and simple methods of generating electricity by spinning a coil of wire in a magnetic field. I do understand from my limited physics knowledge of right-hand-rule that a current will generate as that coil spins, but where are the electrons coming from? Wouldn't you run out of electrons?

Welcome to PF!

You can think of the entire circuit as one continuous wire (with some of that wire coiled-up inside the generator), so there is nowhere for the electrons to go other than around the circuit over and over again.

 

[pinchharmonic]

thanks but then how do you extract energy from that closed loop

 

[russ_watters]

thanks but then how do you extract energy from that closed loop

By resisting that flow.

 

[Evil Bunny]

Whenever electrons leave one side of a source, the same amount come back in the other side. There is no danger of running out...

When they move through the loop and go through a "load", useful things happen. For example when they move through a heating element, they bounce around and bump into each other and that "molecular friction" creates heat that we can use for a variety of things.

When these electrons move through coils of wire (any wire actually, doesn't really need to be a coil), they kick off magnetic fields... in the proper arrangement (like armatures and stators) these magnetic fields will repel and attract each other and make a shaft spin... this is an electric motor.

But always remember... if these electrons are leaving one side of the source, they are always returning on the other side of the source at the same time... this is why there are TWO wires to connect. If they aren't returning... they aren't leaving. And nothing is happening.

These explanations are probably not exactly spot on and someone may correct the details, but this is essentially what is going on.

Hope that helps :-)

 

[pinchharmonic]

By resisting that flow.

russ, when you say resisting that flow I can only think of putting a resistor on the wire that generates heat. i guess i have a more fundamental question then, what is the generator actually creating as its final product. how would it store that energy anyway? is it creating a huge battery?

 

[pinchharmonic]

Whenever electrons leave one side of a source, the same amount come back in the other side. There is no danger of running out...

When they move through the loop and go through a "load", useful things happen. For example when they move through a heating element, they bounce around and bump into each other and that "molecular friction" creates heat that we can use for a variety of things.

When these electrons move through coils of wire (any wire actually, doesn't really need to be a coil), they kick off magnetic fields... in the proper arrangement (like armatures and stators) these magnetic fields will repel and attract each other and make a shaft spin... this is an electric motor.

But always remember... if these electrons are leaving one side of the source, they are always returning on the other side of the source at the same time... this is why there are TWO wires to connect. If they aren't returning... they aren't leaving. And nothing is happening.

These explanations are probably not exactly spot on and someone may correct the details, but this is essentially what is going on.

Hope that helps :-)

i'm trying to visualize what you mean by the same that go in one side, come in the other side.

say you have a wire with a high voltage at one end, and then grounded literally into the ground at the other. my assumption is that electrons flow from the ground to the high voltage end, so in this case I guess the ground won't run out of electrons quickly, but where are the electrons coming from the high voltage end of they come in at both ends?

 

[Evil Bunny]

i'm trying to visualize what you mean by the same that go in one side, come in the other side.

Not necessarily the same exact electron, but if one left (let's say L1) then another one came in (let's say) L2. There are TWO connections on an AC source. One for the electrons that are "coming" and one for the electrons that are "going". They come in one side while simultaneously leaving the other side. Now... obviously with AC the "coming and going" changes with the frequency (usually 60 times a second in the United States).

say you have a wire with a high voltage at one end, and then grounded literally into the ground at the other. my assumption is that electrons flow from the ground to the high voltage end...

No. That is not how it works. Try to forget about the word "ground" when talking about an electric circuit. In "grounded" electrical circuits (like the distribution system in the US), we attach one of the two connections to Earth (EDIT: we attach one of the two connections to Earth AS WELL AS connecting it to the main circuit or main "loop" that we are wanting to do work)... The reason why would be a lengthy discussion for another thread, but as far as we are concerned, the part that is pounded into the ground has absolutely nothing to do with how the circuit works. If you took the section of wire that was buried into the ground and removed it from the AC circuit, it would change nothing about how the circuit works. Electrons that leave the source will always come back to the SOURCE. They don't go into the ground unless the ground is the only way for them to return to the source.

This is a very important point to remember and it is one that throws people off all the time. Many life long electricians don't have this concept down...

so in this case I guess the ground won't run out of electrons quickly, but where are the electrons coming from the high voltage end of they come in at both ends?

They leave one of the poles (L1) of the source... and they come back on the other pole (L2) of the source. Then they leave the other pole (L2) of the source and come back on the first pole (L1) of the source. This repeats back and forth and back and forth (60 times a second, 60 Hz, in the US).

 

[pinchharmonic]

Not necessarily the same exact electron, but if one left (let's say L1) then another one came in (let's say) L2. There are TWO connections on an AC source. One for the electrons that are "coming" and one for the electrons that are "going". They come in one side while simultaneously leaving the other side. Now... obviously with AC the "coming and going" changes with the frequency (usually 60 times a second in the United States).



No. That is not how it works. Try to forget about the word "ground" when talking about an electric circuit. In "grounded" electrical circuits (like the distribution system in the US), we attach one of the two connections to Earth (EDIT: we attach one of the two connections to Earth AS WELL AS connecting it to the main circuit or main "loop" that we are wanting to do work)... The reason why would be a lengthy discussion for another thread, but as far as we are concerned, the part that is pounded into the ground has absolutely nothing to do with how the circuit works. If you took the section of wire that was buried into the ground and removed it from the AC circuit, it would change nothing about how the circuit works. Electrons that leave the source will always come back to the SOURCE. They don't go into the ground unless the ground is the only way for them to return to the source.

This is a very important point to remember and it is one that throws people off all the time. Many life long electricians don't have this concept down...



They leave one of the poles (L1) of the source... and they come back on the other pole (L2) of the source. Then they leave the other pole (L2) of the source and come back on the first pole (L1) of the source. This repeats back and forth and back and forth (60 times a second, 60 Hz, in the US).

Evil Bunny,

Thanks for the answer, so in other words it's like having a long glass tube with sand and u let the sand slide one way, then the other way 60 times per second? I guess that makes more sense with the turbine generating energy because it's generating an alternate current in that loop of wire right?

Then I guess my previous question about a wire with a high voltage to the ground was more of a DC. No alternating current, like a battery.

say for example I had a really high voltage battery, and I connected a wire to the positive terminal, then i connected the other end into the ground. Would the ground have enough potential difference to draw current? And in that case do the electrons really just go into the ground and disperse at least until the high voltage potential of the positive terminal goes down enough no current is drawn?

 

[Evil Bunny]

No. A battery is no different. It will go from negative terminal to positive terminal. It just will never change direction like AC. You can't drain a battery unless you connect both terminals in a circuit. One post connected to the ground will do nothing.

 

[pinchharmonic]

Evil Bunny,

This came up in another thread from Ivan Seeking

btw, the short answer: Electrons that flow in dc circuits come from ground - the earth. This was implied but I don't think anyone ever said it. The world's economy now depends on good ground rods.

I always found the drift velocity funny to consider. In a 12 gauge wire carrying ten amps, vd is about 0.036 cm/sec.

And then someone else responds wtih:

In the case of a generator which does not have a return line, electrons are "pumped" from the ground to elevated potentials by the generator. The conductors then transport electrons and energy to a load, where the electrons then return to ground, returning the energy gained at the generator.

If the generator is not connected to a "earth" ground then the return path must provided. In this case electrons are simply "pushed" through the circuit by the generator.

Isolated circuits must have a means of moving electrons or a source of electrons. The source can be a chemical reaction as in a battery or a atomic change in state as in a Photovoltaic cell.

Do not get the idea that only electrons can be current carriers, in ionic solutions the ions, both positive and negative can be current carriers.

so give what you mentioned earlier, in regards to the first post about ground rods, to me even in a DC generator you should not need a ground rod in theory. The electrons you pull from the ground will eventually go back to the ground as part of your circuit, so using the ground I suppose is just to get the lowest possible voltage for efficiency purposes.

and one question about the generator, the guy mentions a rod in the ground and above it a high potential atttracting electrons at the top, then a capacitor so the electrons basically collect at the left side of the capacitor wall. So i visualize that line coming from the ground with a flow of electrons to the top as being the line that can power light bulbs, and other day to day things that need electricty, or just a flow of electrons.

Now what happens when too many electrons pool on that left side of the capacitor, don't they start to make the charge closer to zero or negative and start repelling? Given that, the DC generator seems like it may need to close the capacitor at some point and let all the electrons go back down the return line (at this point i think the ground itself will be positively charged since so many electrons were removed) and then things back into balance?

 

[russ_watters]

russ, when you say resisting that flow I can only think of putting a resistor on the wire that generates heat.

That's one way, yes.

i guess i have a more fundamental question then, what is the generator actually creating as its final product.

It's "creating" motion in pre-existing electrons.

how would it store that energy anyway? is it creating a huge battery?

Generators do not store energy.

I think it would be best if you didn't confuse yourself with AC current yet, and get comfortable with the idea that in a DC circuit, a generator will just push electrons around in a circle.

 

[pinchharmonic]

That's one way, yes. It's "creating" motion in pre-existing electrons. Generators do not store energy.

I think it would be best if you didn't confuse yourself with AC current yet, and get comfortable with the idea that in a DC circuit, a generator will just push electrons around in a circle.

thanks russ, yea I read another old thread (which you were a contributor to), with the analogy of a pipe with ping pong balls, that makes a lot of sense to me.

Now I'm trying to understand the DC generator concept that someone mentioned in that thread, where electrons are drawn from the ground literally, to some potential above to collect onto a capacitor. I figure that path of the electrons from ground to the high potential is the current that can power things we need electricity for. I just get confused what happens over time when so many electrons collect there and eventually make that voltage go down to nothing or even negative, wouldn't that DC generator need a "reset" like connecting the plates of the capacitor to let all the electrons go back to the ground, which at this point is probably positively charged since it lacks electrons?

 

[Drakkith]

Pinch, a DC generator needs to be connected to a circuit. It simply moves the electrons around in that circuit from one end to the other end. Each individual electron takes a long time to get around the circuit, but that is because at anyone time there are many different electrons actually moving around. That means that the first electrons to move aren't the only ones to move. They move which forces others to move and so forth down the line. The combined movement of all these electrons causes current.

 

[Evil Bunny]

Electrons that flow in dc circuits come from ground - the earth.

This could not be more false. The electrons that flow in a dc circuit "come from" the negative post and flow "into" the positive post of the battery. This is what happens. The "ground" has nothing to do with this fact. (I'm trying not to introduce drift velocity into this conversation because it will only confuse the issue).

If you took a volt meter and measured voltage from the ground to the negative post, your meter would read 0 volts. If you took a volt meter and measured voltage from the ground to the positive post, your volt meter would read 0 volts. I promise you this. If you don't believe me, please go try it.

Your volt meter will not measure a voltage from the positive post of one battery and the negative post of another battery either. The ONLY way you will measure a voltage from a battery is to measure the voltage between the two posts of the same battery. (unless they're connected together, which is a whole different scenario)

In the case of a generator which does not have a return line, electrons are "pumped" from the ground to elevated potentials by the generator. The conductors then transport electrons and energy to a load, where the electrons then return to ground, returning the energy gained at the generator.

There is no such thing as a generator that does not have a return line. The only thing I can imagine this person was talking about is that they connected the "return" line to the Earth and they used the Earth as a path back to the source.

(Unless you're talking about something like a http://en.wikipedia.org/wiki/Van_de_Graaff_generator" which has to do with static electricity and is an entirely different conversation.)

 

[trand]

how would it store that energy anyway? is it creating a huge battery?

Think of the generator as simply an energy converter. It doesn't store any energy itself, it simply uses magnetic fields, which are propelled externally, to move the electrons around. So when you apply certain mechanical energy to the generator it is transferred over to the electrons and as nature loves to neutralize everything, the electrons essentially start moving as a chain, instead of building up into some unstable superion. So electrons don't 'come' from anywhere, they exist at all times and when you move them, you've found a practical way of transferring energy between different bodies.

 

[Evil Bunny]

say you have a wire with a high voltage at one end, and then grounded literally into the ground at the other.

Didn't catch this before... You cannot have a high voltage at "one end". Voltage is a measurement between two points. If you have a high voltage at one end, then it is high with respect to "the other end".

Let's say you have an imaginary 200V battery sitting on the ground... You take your meter leads and put them on each post. Your meter reads 200VDC. No problem. You expected this...

You now take your meter and put one lead on the + terminal and stick the other lead into the ground. Your meter reads 0V. The same happens when you put one lead on the (-) terminal with the other lead stuck into the ground. Your meter reads 0V.

Now here is the ground part you're interested in... Let's say that now you attach a large wire to the (-) post of the battery and stick the other end of that wire into the ground. Nothing is attached to the + post of the battery...

Now you take your meter and stick one lead on the + post of the battery and stick the other meter lead into the ground and you will measure a voltage (assuming you are close enough to the wire that is stuck into the ground).

This is the only scenario where you will get electrons to flow into the ground from a battery... and this only happens because the ground is the only way back to the source... the ground completes the loop here. They don't end up in the ground, they are just traveling through the ground to make it back to the source.

 

[pinchharmonic]

Didn't catch this before... You cannot have a high voltage at "one end". Voltage is a measurement between two points. If you have a high voltage at one end, then it is high with respect to "the other end".

Let's say you have an imaginary 200V battery sitting on the ground... You take your meter leads and put them on each post. Your meter reads 200VDC. No problem. You expected this...

You now take your meter and put one lead on the + terminal and stick the other lead into the ground. Your meter reads 0V. The same happens when you put one lead on the (-) terminal with the other lead stuck into the ground. Your meter reads 0V.

Now here is the ground part you're interested in... Let's say that now you attach a large wire to the (-) post of the battery and stick the other end of that wire into the ground. Nothing is attached to the + post of the battery...

Now you take your meter and stick one lead on the + post of the battery and stick the other meter lead into the ground and you will measure a voltage (assuming you are close enough to the wire that is stuck into the ground).

This is the only scenario where you will get electrons to flow into the ground from a battery... and this only happens because the ground is the only way back to the source... the ground completes the loop here. They don't end up in the ground, they are just traveling through the ground to make it back to the source.

thanks evil bunny, that made a lot of sense. So in other words the ground is just completing the circuit.

I guess I have to do more research now on batteries for example, because, as you pointed out before, I incorrectly assumed the ground on a battery is no different then the ground we walk on.

so what if i connect the + of one battery, to the negative of another battery? wouldn't that short the wire similarly?

or is the potential difference unique to the battery itself?

 

[pinchharmonic]

Think of the generator as simply an energy converter. It doesn't store any energy itself, it simply uses magnetic fields, which are propelled externally, to move the electrons around. So when you apply certain mechanical energy to the generator it is transferred over to the electrons and as nature loves to neutralize everything, the electrons essentially start moving as a chain, instead of building up into some unstable superion. So electrons don't 'come' from anywhere, they exist at all times and when you move them, you've found a practical way of transferring energy between different bodies.

thanks trand. now I'm curious what happens in a DC circuit when there is a capacitor? even if the electrons move slowly, they end up stuck at one end of the capacitor wall building up a negative charge until they repel back right?

what if a city was powered by DC, so the outlet had a + and -, and then someone decides to just attach a circuit with a capacitor there. woulnd't that circuit stop all the electrons from going back the return loop?

And also, if a city was powered by a DC, wouldn't, over time, the same electron that was pushed from the generator, come back all the way through town back to the generator?

 

[Evil Bunny]

so what if i connect the + of one battery, to the negative of another battery? wouldn't that short the wire similarly?

No it would not be a short circuit. What you just did was wired the batteries in series and their voltages add up. If they were both 12 volt batteries, you would now measure 24 volts between the + of the first battery (that has it's negative tied to the other battery) and the negative of the other battery (that has it's positive tied to the first battery's negative). Draw it out if it sounds confusing...

or is the potential difference unique to the battery itself?

It's unique in the sense that you need to have a complete circuit in order to utilize the voltage potential... but as you can see, it can be wired together with other batteries and work in conjunction with them.

As for capacitors in a DC circuit... yes, if you hooked a capacitor up to a battery it would charge up to the DC source voltage and then stop. If that was the only thing in the circuit, then yes everything would stop. You would have an open. One would hope that in your DC city, they would wire the houses in parallel and not in series, so this open circuit would not shut down the rest of the city! And lastly, yes that lone electron that left the negative side would eventually make it's way all the way back to the positive side of the source. It might take years though! lol

 

[pinchharmonic]

No it would not be a short circuit. What you just did was wired the batteries in series and their voltages add up. If they were both 12 volt batteries, you would now measure 24 volts between the + of the first battery (that has it's negative tied to the other battery) and the negative of the other battery (that has it's positive tied to the first battery's negative). Draw it out if it sounds confusing...




It's unique in the sense that you need to have a complete circuit in order to utilize the voltage potential... but as you can see, it can be wired together with other batteries and work in conjunction with them.

As for capacitors in a DC circuit... yes, if you hooked a capacitor up to a battery it would charge up to the DC source voltage and then stop. If that was the only thing in the circuit, then yes everything would stop. You would have an open. One would hope that in your DC city, they would wire the houses in parallel and not in series, so this open circuit would not shut down the rest of the city! And lastly, yes that lone electron that left the negative side would eventually make it's way all the way back to the positive side of the source. It might take years though! lol

evil bunny, thanks that nailed it for me conceptually now.

Now I want to understand a bit more on the physics behind the potential differences, whether from batteries, or from a generator. From a generator it seems to be since electricty and magnetism are tied, you can use that to your advantage to generate a current spinning a loop of wire in a magnetic field -- but it's really just creating a potential difference that moves the electrons right?. I see it as the same concept as an electric motor but in reverse.

and in the battery's case there is a high voltage(+) and a low voltage(-), what I now understand is that the battery must be internally connected in between the + and - as you said, otherwise the circuit is open and the flow won't work properly. I read somewhere that internally a battery has a resistor between its + and -. Since it's a resistor, isn't current still flowing through it, and is that why battery's degrade over time?

 

[Evil Bunny]

You seem to have the physics of a generator down... It's nothing more than a conductor interacting with a magnetic field and creating a potential difference. If the ends of the wire that have this potential difference are connected together (preferably with some type of load in between) and the loop, or circuit, is completed, then we have current flow.

As for batteries... this is a bit more complicated and involves chemistry. I will leave that explanation for somebody else. There are plenty of people around here who know a whole lot more about it than I do... As far as I'm concerned, it's a magic box that I can use as a voltage source :-)

 

[Pythagorean]

evil bunny, thanks that nailed it for me conceptually now.

Now I want to understand a bit more on the physics behind the potential differences, whether from batteries, or from a generator. From a generator it seems to be since electricty and magnetism are tied, you can use that to your advantage to generate a current spinning a loop of wire in a magnetic field -- but it's really just creating a potential difference that moves the electrons right?. I see it as the same concept as an electric motor but in reverse.

and in the battery's case there is a high voltage(+) and a low voltage(-), what I now understand is that the battery must be internally connected in between the + and - as you said, otherwise the circuit is open and the flow won't work properly. I read somewhere that internally a battery has a resistor between its + and -. Since it's a resistor, isn't current still flowing through it, and is that why battery's degrade over time?

No, the terminals aren't connected internally or they'd short out. Capacitors and batteries are very similar. I would say a major difference is that batteries can store charge more long term, but the naive macro physics are essentially the same.

The back emf (the internal resistance) isn't a real resistor. The current must go from I = 0 to some value as you fire up the circuit. Even when the batteries been on a while, the electrons initiating from the anode are still speeding up from 0 mph to X mph, thus generating a small change in current.

The change in current induces a change in flux, but nature abhors a change in flux, so it resists that change, which cascades back down to a resistance in the current (so this is all coupled through the magnetic field).

There is no actual charge motion current flowing inside the battery between terminals.

 

[sophiecentaur]

There is no actual charge motion current flowing inside the battery between terminals.

There must be a flow of charge inside the battery or there would be no electrons to shove out of the negative terminal and no room for electrons to flow into the positive terminal. The result of this charge flow is deposition of atoms on the battery plates.

 

[RedX]

As has been mentioned in the very first post, electrons flow in the wire from the negative terminal to the positive terminal, and some sort of positive ion flows inside the battery solution from the negative terminal to the positive terminal. The electrons and the positive ions combine at the positive terminal and together with the atoms of the positive terminal, form a neutral atom. The energy of the reaction per electron produced is the voltage.

 

[pinchharmonic]

As has been mentioned in the very first post, electrons flow in the wire from the negative terminal to the positive terminal, and some sort of positive ion flows inside the battery solution from the negative terminal to the positive terminal. The electrons and the positive ions combine at the positive terminal and together with the atoms of the positive terminal, form a neutral atom. The energy of the reaction per electron produced is the voltage.

thanks, can you explain how the energy is extracted out of that reaction per electron produced? I'm still a bit confused what exactly is causing the potential difference between the terminals

and I'm assuming earlier you meant the electron was created (or cleaved) from the atom which resulted in the positive ion?

 

[RedX]

thanks, can you explain how the energy is extracted out of that reaction per electron produced? I'm still a bit confused what exactly is causing the potential difference between the terminals

and I'm assuming earlier you meant the electron was created (or cleaved) from the atom which resulted in the positive ion?

You pretty much understand it as much or better than I do, based on your first post.

One terminal of the battery gives electrons to the circuit, and the other takes electrons from the circuit, and positive ions flow in the battery solution from the side that gives electrons to the side that takes electrons.

Whether a chemical reaction takes place or not depends on thermodynamics. The negative terminal of the battery badly wants to give an electron away, and the positive terminal badly wants an electron, so if you connect one terminal of the battery to one metal plate, and the other terminal to a different metal plate, then the positive terminal will steal electrons from the metal plate so that it can complete its reaction, and the negative terminal will give electrons away to the metal plate so that it can complete its reaction. But eventually this reaction will stop because the positive plate becomes very positive in charge, and the negative plate becomes very negative in charge, so there are strong electrical forces which stops the shedding and accepting of electrons which are governed by chemical forces. Basically the metal plate tells the negative terminal that it has so many electrons on it that it doesn't care if the negative terminal chemically wants to give it another electron - enough is enough, and until you can get rid of some electrons on the negative plate, the reactions stop.

But if you connect the two metal plates to make a circuit with the battery, then the electrons on the negative plate will be very happy to flow to the positive plate and into the positive terminal, so that more electrons can be produced chemically at the negative terminal since the negative plate was relieved of electrons so there is no electrical force to stop the chemical reactions. The electron is very excited to go to the positive terminal (and the positive terminal is excited to be getting electrons to complete its own reaction). This excitement translates to kinetic energy of the electron that can do work through a resistor: resistance will not stop the electron from going through the circuit, because the electrons want to keep the terminals happy, i.e., keep the chemical reactions going.