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!