Voltage Increases When Connecting Multiple Batteries

[scientifico]

Hello, why when I connect 2 or more battery in series the voltage at the extremes of batterys will be the sum of single batteries voltages? what happen phisically?
how the electrons of second battery go to the positive pole if they must pass from the first battery?

Thanks!

 

[jvclark2]

To answer your question let's make a simple picture
A---------(-V1+)------------(-V2+)----------B,
o-->
where V1 and V2 are your batteries. When an electron travels from point A and passes through point V1 there is a rise in the electric potential energy of the electron, similar to water flowing if you imagine the water going uphill at V1 and V2. Each rise will increase the potential energy, both by V1 and V2. The key thing to realize is that each battery is just a voltage gain. The "positive pole" you are referring to is kind of a misnomer. The plus sign just indicates which end of the battery is at a higher relative electric potential.

For the details behind what physically happens to batteries I would recommend quickly going over this site: http://en.wikipedia.org/wiki/Battery_(electricity)#Principle_of_operation

 

[sophiecentaur]

Talking in terms of electrons flowing round really does make life harder. In a low power circuit, an electron has an average speed of much less than 1mm/second. So much so that, with a longish piece of wire in the circuit, a watch battery will be flat before an electron gets from one terminal, round the circuit and back to the other terminal. Despite the slightly more abstract model, it really does make more sense to talk in terms of charge flow (which is the net effect of zillions of electrons in extremely fast, random motion and with an extremely low mean velocity). The Electrical Potential Differences across the two cells gives the charge two lots energy which is dissipated in the elements of the circuit (resistor / lamp /motor etc). The higher the total Potential difference, the more energy each Coulomb of charge dissipates.
imho, the electron flow model is such an oversimplification that it actually detracts from understanding what is going on and damages the possibility of a good understanding.
One Volt of potential gives one Coulomb of Charge one Joule of energy. The volts just add up.

 

[jim hardy]

there's a pretty down-to-earth explanation of the difference between current and electron motion here:


http://amasci.com/miscon/speed.html

it's written by a hobbyist wth a knack for explaining things.
would be interesting to delve into his references.

old jim

 

[sophiecentaur]

I think he gives a good description. I'm not sure he's really prepared to give enough of an opinion as to how useful it may be to use one approach or another. Perhaps he reckons it's not his job. Fair enough.
He definitely pours cold water on the model that is implied in the way school kids are taught. This is good; all Science teachers should be required to read it.

 

[scientifico]

If I measure an electrical potential difference of 32 V it means every electron has the power of 32 Joule?
Is the speed of electricity related to its potential difference or current?

Thanks!

 

[NascentOxygen]

If I measure an electrical potential difference of 32 V it means every electron has the power of 32 Joule?
Is the speed of electricity related to its potential difference or current?

Thanks!

A volt is defined as a Joule per coulomb.

Greater current means more electrons are flowing.

 

[sophiecentaur]

If I measure an electrical potential difference of 32 V it means every electron has the power of 32 Joule?
Is the speed of electricity related to its potential difference or current?

Thanks!

"Speed of electricity" is not a meaningful quantity because "electricity" is not a defined quantity (try to look it up). As stated earlier, the mean drift speed of electrons is around 1mm/s but the speed that the effect of turning on the supply will propagate at not far short of the speed of light.

 

[scientifico]

but a 32 V current flow is moving a bit faster than a 12 V current flow if they both have the same amperage and in the same material like Cu, right?

 

[sophiecentaur]

Go and do the sums. The formula for drift velocity is available all over the place. You need to get this in proportion. Find out the numbers involved before you say "surely".

 

[scientifico]

I've seen the drift velocity formula and it's proportional to the current instead of voltage but why?
Doesn't more energy mean more speed available?

 

[sophiecentaur]

Ideas about drift velocity tend to be based on intuitive 'mechanical' thinking - water wheels and the like. If you think in terms of a wide velocity distribution of conduction electrons and that a potential difference is just going to change the probability of a direction of motion by a minuscule amount, would that make more sense?

 

[Windadct]

The last time I discussed Drift Velocity was in an EE class ( in the 80s) - I have never seen any practical application of the topic - it is more of a material science issue, current density of material etc. Really has nothing to do with the circuit, power etc - and nothing to do with the battery case of the OP.

 

[sophiecentaur]

Absolutely. But people insist on a flowing water / KE explanation and drift velocity shows it's not like that.

 

[scientifico]

The way I think is the more voltage is applied the more electrons' speed increase because higher voltage = more energy = more speed
I think an higher energy object can be more speed than a low energy one but in the drift velocity formula only appears the current not the voltage so what are the errors of my reasoning?

Thank you!

 

[sophiecentaur]

But it ISN'T like Kinetic Energy. The KE of the electrons is absolutely microscopic. You need to remember that or you will draw some very wrong conclusions. Like I said before, it isn't the Kinetic Energy in your (very low mass) bicycle chain that takes the power to the wheels - and it's not even the speed at all, because you can be in a range of gears for the same power transfer.

 

[scientifico]

if not more speed, how can be imagined an electrons flow at low voltage and at high voltage?
for "change the probability of a direction of motion" you mean the higher the voltage is the more electrons will be physically "involved" in the current flow?

 

[sophiecentaur]

I am saying that the Kinetic Energy is IRRELEVANT and is of no significance in the transfer of energy.
To say otherwise is to give the wrong impression.

 

[NascentOxygen]

The way I think is the more voltage is applied the more electrons' speed increase because higher voltage = more energy = more speed

That applies to the electron beam in a cathode ray tube (CRT).

I think an higher energy object can be more speed than a low energy one but in the drift velocity formula only appears the current not the voltage so what are the errors of my reasoning?

If you apply more voltage to the sea of swirling electrons in a wire, then it's a case of more electrons getting pushed along, rather than the original number being pushed faster.

 

[jim hardy]

it is more similar to the pv term in fluid flow, potential energy from pressure,
than it is to mv² as in kinetic energy from velocity.

 

[sophiecentaur]

His whole model pre-supposes that the model of water rushing through pipes is the right one.
I wonder whether he has considered just why the term 'Potential Difference' is used.

 

[jim hardy]

I have finally realized that's the trouble with the water analogy - it's natural for folks to think immediately of a fire hose.

If you ever held the nozzle of, say, a hundred horsepower fire pump you have a really visceral feel for difference between pressure and velocity.

old jim

 

[sophiecentaur]

It's good to get your feet wet in a new topic occasionally.

 

[scientifico]

If you apply more voltage to the sea of swirling electrons in a wire, then it's a case of more electrons getting pushed along, rather than the original number being pushed faster.

But doesn't more electrons pushed along mean an higher current insted of an higher voltage?

thank you

 

[sophiecentaur]

Some while back there was reference to the formula for drift speed. Anyone who hasn't looked it up really should do so if they want to contribute to this particular sub-thread.
If you want to be a 'real Scientist' you will be aware that most phenomena have many factors. The fact that some very low-mass particles (perhaps 1/20000 of the mass of the metal) are moving Very Slowly cannot account for any significant amount the Energy Transfer. Why is this aspect of an electric current a cause for such obsession still?

Of course, Current is rate of transfer of Charge so more electrons go past a given point when the current is higher. They are obviously moving and the mean speed depends, as the formula tells you, on the current. For an Ohmic material, the current will depend upon the Potential Difference and the Resistance so, if it makes you feel better, you can say it relates to Voltage.
If you were to heat up the wire, there would be less current flowing and the electrons would be moving slower for the same PD.
But SO WHAT? It's all irrelevant to the energy that is being transferred. If you want to get a useful idea about 'how electricity works' you need to consider the relevant factors and not get distracted by stuff that doesn't count.

Models in our heads can often lead to a really poor understanding because they can be just plain wrong. It may be OK when it's in one's own head but it's not fair to promote the idea of a flawed model to people who are desperate to learn what's going on.

 

[jim hardy]

Models in our heads can often lead to a really poor understanding because they can be just plain wrong. It may be OK when it's in one's own head but it's not fair to promote the idea of a flawed model to people who are desperate to learn what's going on.

Sophie, if it's flawed it's flawed and doesn't belong in one's own head.

One has to test and refine his 'mental models' until they come in agreement with nature, because our mind accepts myth as readily as fact.. That was Francis Bacon's point.

I suspect it's a fortunate few who've had the combination of time and opportunity to really go back and refine their basics. We rush through engineering college and off into a hurry-scurry world where success is measured by how far removed one gets from the machinery or factory floor or design desk, the very places where basics are most directly applied.

The world needs more "Trustees from the Toolroom".

 

[sophiecentaur]

Sophie, if it's flawed it's flawed and doesn't belong in one's own head.

One has to test and refine his 'mental models' until they come in agreement with nature, because our mind accepts myth as readily as fact.. That was Francis Bacon's point.

I suspect it's a fortunate few who've had the combination of time and opportunity to really go back and refine their basics. We rush through engineering college and off into a hurry-scurry world where success is measured by how far removed one gets from the machinery or factory floor or design desk, the very places where basics are most directly applied.

The world needs more "Trustees from the Toolroom".

I agree, in principle but I'd bet you have little quirky ways of thinking about things that are a bit approximate but get you the result. For instance, I always think of 'up and down' on a circuit diagram, which I usually get away with, except with an electrolytic drawn horizontally. It works for me but I wouldn't dream of inflicting it on anyone else.

I was lucky to spend 24years in Engineering Research, where we were actually PAID (cor blimey) for polishing up our ideas again and again because we couldn't afford to get things wrong. A real luxury - but a two edged sword because I was always realising just how dumb I was.

As you say "flawed is flawed". I think I was just trying a slightly less brutal put down when I made my original remark about it. It really pees me off when people try to 'explain' things with their own weird models.

 

[jim hardy]

I agree, in principle but I'd bet you have little quirky ways of thinking about things that are a bit approximate but get you the result.

That's doubtless so.

I read a LOT of Isaac Asimov in 60-s through 80's and have always tried to emulate his step-by-step approach to explaining things.
I was tolerated in the power plant because of my ability to explain things simply, which helped the guys a lot in their troubleshooting. So over the years i too got to sort out what worked and what didn't, though in an industrial work environment. I made my share of mistakes, i assure you.

One thing i noticed early on was the extreme competence of 60's-70's era Navy Nukes. Their training methods should be studied.

 

[jim hardy]

oops - accidental hijack...

 

[scientifico]

it's more correct to think of billions of electrons agitated for themself and a potential difference just add energy to this huge chaos of electrons and attract them to the opposite pole (positive)?
So the will the electrons nearest the positive pole have slight more energy than the farest ones?
Thank you!

 

[sophiecentaur]

That's what Potential Difference is all about. Although, with an attractive force, the Energy is defined as Negative. For a wire made of a highly conductive metal the PD across the length will be tiny.

 

[scientifico]

the Energy is defined as Negative

mean that conventionally the energy flows from the plus to the minus?

For a wire made of a highly conductive metal the PD across the length will be tiny.

What do you mean for "across the length" ?

 

[sophiecentaur]

mean that conventionally the energy flows from the plus to the minus?

What do you mean for "across the length" ?

Negative energy applies to an 'attractive' system in which energy is produced when two objects get closer - a waterfall produces useful energy because the (gravitational in this case)potential energy is less at the bottom than at the top. I am not referring to the electrons specifically having a negative charge. You could just as easily talk about positive charges moving to the negative terminal (the conventional way).

By "Across the length" I mean 'as opposed across the width' of the conductor. The PD over the whole length of the conductor is still small.

 

[Windadct]

IMHO - the "Negative Energy" term is really just confusing this issue. Energy moves (converted) from one system to another, a positive or negative reference only applies to the point of observation or the difference in two or more states ( top of the waterfall vs bottom of the waterfall, battery before the current flows vs after the current flows) They have less energy, but they do not negative energy.

For battery energy does NOT flow from one terminal to another, IN the battery a chemical system has potential energy stored ( I would never think of this as negative) and it creates EMF ( Electro Motive force / voltage) but a force alone is not energy but in pretty much all systems indicates that there is some energy present. In the simplest case when the positive terminal and negative terminal of the battery are connected by some form of a conductor, the chemical potential energy is converted into electrical energy - in the case of a simple wire - essentially ALL of the energy is converted to heat energy.

You can refer to the difference of energy - being negative.

Back to the OP - two batteries in series, the Electro-Motive Force (voltage) is added - the force sums as does the potential energy of the two batteries. Note if you have 2 equal batteries - you always have 2 x the energy - how you connect them is irrelevant.
In the waterfall analogy - think of 2 waterfalls - on on top of another - if the water is 2x as high - it has 2 x the potential ( relative to the bottom of the waterfall)

As for the Potential Difference (PD) "Across the Length" of the conductor - it has to equal the potential applied - assuming from the battery, so I am missing the "is still small" reference. ( Since a battery is not a perfect device - it also has internal resistance - which will see some voltage if you short circuit the battery with a wire - but that discussion is also off topic of the OP)

Sorry to bring some "Negative Energy" to the thread.

 

[scientifico]

An high potential difference pratically means that more work is relased when a coulomb move from the lower point to the higher, and a low PD less work for the same coulomb?
Why in some places is written that the energy is needed to move a charge istead of relased when a charge move, who is right?

When I connect the 2 poles of a battery the first electrons moving are the one near the positive but they can be too the electrons of the metal wire right?

 

[Windadct]

You are correct that moving a charge across a lower PD ( field) absorbes or releases less energy then in a higher PD ( field). In all cases energy is needed ( source ) and is transferred to something else. "Energy needed" "consumed" etc are all a matter of perspective (are you the circuit or the battery)- for this a rechargeable battery is a good model - you have to ADD energy to the battery to charge it - and it delivers energy when it discharges. This is a basic physics model.

The point of the battery is that it generates a voltage, this voltage acts on all of the electrons in the conductor the same way - there is not more action near one terminal of the battery.

It is the presence of the voltage that acts instantly ( technically some speed slightly slower then the speed of light across a conductor) - this voltage make (pushes/pulls) all of the electrons in the conductor at the same time.

Thinking of how the electrons move in an conductor - is 2 -3 levels or more than is required to discuss the OP. When you put 2 batteries in series the voltages add - this is a basic circuit question. How electrons flow in a conductor when a voltage is applied, is physical science ( still an electrical engineering discipline ) - but is not directly related to how a battery operates. Part of the beauty of Electrical Engineering is how well the real world application matches the theory AND how well the theory can be broken into very simple elements. So mixing the discussion between the three or four concepts in this thread - is really only making is much more difficult. Batteries/Energy/EMF/Electron flow - each requires their own study - then you can better understand how they interact - but in reality you almost never need to think of them all at the same time to solve any problem.

 

[scientifico]

The force that act on electrons is provided by the positive charges, so teorically if i connect a piece of wire only to the positive pole, is there a possibility that some electrons of the wire go to the +?

Thank you!

 

[sophiecentaur]

IMHO - the "Negative Energy" term is really just confusing this issue. Energy moves (converted) from one system to another, a positive or negative reference only applies to the point of observation or the difference in two or more states ( top of the waterfall vs bottom of the waterfall, battery before the current flows vs after the current flows) They have less energy, but they do not negative energy.

Yes, I have to agree with you there. It may be true bit it isn't really relevant.

This thread is a great example of one which is being driven by a diehard misconception about electrical energy transfer. The Schoolboy model of electrons along wires is so attractive and 'pictorial' that it makes people hang onto it long past the point where they should be looking for something deeper.

The fact is that Electrical Energy transfer is a very sophisticated process. There is no satisfactory description at an elementary level. Along with all the other difficult concepts in Physics (QM, Relativity etc,) , if you think you've 'got it', then you probably haven't.

I had a huge advantage in being 'taught' Electricity without the use of noddy electron picture models. You go straight into a simple mathematical treatment and it yields all the measurable behavior of circuits and emerge with confidence about those tangible things. Later on you talk about conduction and electron motion in a vacuum and the QM aspects of it all. At no stage was there any need to 'demand' an 'understandable' model.

The way things are going seems to be little more than the blind leading the blind (delivery of the Electricity Curriculum in School, for instance) and with no one being prepared to get down and dirty with some serious basic theory. "In my day" conversations like this were short and sweet because people accepted that they don't really get you anywhere.

 

[sophiecentaur]

The force that act on electrons is provided by the positive charges, so teorically if i connect a piece of wire only to the positive pole, is there a possibility that some electrons of the wire go to the +?

Thank you!

You are describing what is referred to as an Incomplete Circuit. No steady current will flow, of course. But when the wire is first connected, there will be a small (and just detectable) charge flow, until the fields balance out. If, instead of a wire, you use a pair of plates, closely spaced and with a large area (same thing conceptually) then you get a Capacitor and a very significant charge will flow which will 'charge' the capacitor until, again, the fields balance out.

 

[scientifico]

So if I just connect a wire to the positive pole (creating an incomplete circuit) there will be no steady current because the protons of the wire will not permitt the wire electrons to move away to the positive pole of the battery?
So, if the positive of the battery would have a very big potential difference and for example the wire is heated, is it possible to remove electrons from the wire?

Thank you!