EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: challie2 on September 19, 2020, 03:38:48 pm
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Hi everyone, I am trying to learn about electronics.
Now I understand what happens when you take a wire and place it across the positive and negative of the same battery, electrons flow and the battery shorts out. However if you have 2 identical batteries and attach the positive of one battery to the negative of another battery, why do they not short out this time, when the positive and negative of both batteries are identical in every way? As all the flow of electricity cares about is to flow from positive to negative? Why do you have to then place another wire across the remaining opposite poles? I have attached a photo to illustrate my question.
Thanks
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As all the flow of electricity cares about is to flow from positive to negative?
This is not correct. Electricity cares about going round in closed loops. If there is no loop, there is no flow.
When you join batteries end to end without completing the circuit there is no loop, therefore no flow can happen.
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Your drawing of the two batteries has no return path (it is open circuit) so there can be no current flow.
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So where I think im getting confused is assuming the positive and negative of separate batteries will create a closed loop. How is it different? Thanks
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In other words what stops it from being a closed loop?
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So where I think im getting confused is assuming the positive and negative of separate batteries will create a closed loop. How is it different? Thanks
A closed loop is literally what it says. It is where you can start with your pencil, go round the circuit without any breaks, and end up back where you started. How can you do that with your two batteries connected end to end?
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But what im confused with is it is still a positive to negative connection but just between different batteries. what makes stops it shorting in this instance when the positive and negative of both batteries are identical. Im just not understanding. ☹️
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Reread the replies above. You must have a loop for current to flow. Just connecting two terminals won't do it unless that closes a loop. "Shorting out" isn't a good description. "Closing loop" is better. Don't let the language inhibit your understanding.
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You're asking a basic but valid question that is difficult to answer in some ways.
For the most part, in electronics, we think of voltage potential as relative. Your 9 volt battery has about 9 volts more potential on the positive terminal than on the negative. Voltage potential can also be thought of in terms of absolutes. An isolated object with an equal number of positive and negative charges--protons and electrons--will have an absolute voltage of zero volts. Your 9 volt battery just sitting on the table could have an absolute potential of many hundreds of volts and you wouldn't notice.
So what happens when you connect the positive of one with the negative of another? So let's posit that at the start, the each battery has an absolute charge of zero at at the negative terminal and since they are 9V batteries, 9 volts at the positive terminal. So what will happen is that when you connect them, a very small amount of current will flow from the positive to the other negative until the potentials are equalized at the connected terminals. You will then have one battery with an absolute charge at its negative terminal of more than zero and one with less. This amount of current is so small that at those voltages and with direct current, it is generally not worth mentioning--but it does exist. And since the starting absolute charge of the battery will be pretty random, there won't be any usable or predictable result.
In an actual circuit, you usually have to give the electricity a complete path to flow through for it to do any useful work, otherwise the potentials will just float up or down until they balance as in our example. To learn more you should use Google or Wikipedia or something and look up electrostatics, Kirchoff, Thevenin and Norton.
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However if you have 2 identical batteries and attach the positive of one battery to the negative of another battery, why do they not short out this time, when the positive and negative of both batteries are identical in every way?
You can imagine electricity in the wire like water in the pipe. In order to do water flow, there is need for a water pump. When the pipe is connected in a loop around water pump, then water pump can make water flow in the pipe. But if you break pipe and put hose plugs on it, then water cannot flow through pipe. The same happens when you break wire loop across battery terminals. Water pump here is a battery. + and - terminals on the battery is a water pump input and output. :)
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You need a continuous path for the electrons to flow through. Electrons are an actual thing, even though they are so very, very small that you cannot see them.
The water through a pipe analogy above helps to illustrate the issue.
The voltage is the electron pressure, just like the pressure in a pipe.
The current is the electron flow, just like the flow through a pipe
If you increase the size of a pipe, more water can flow through easily, even at a low pressure.
If you add some sort of resistance, like a narrow stretch of pipe (think of trying to breathe through a straw instead of a paper-towel tube) it will take more pressure to cause things to flow at higher and higher rates, etc.
The electrons will not be pushed/sucked in/out of the adjoining item unless there is a closed circuit for them to flow around the loop through.
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But what im confused with is it is still a positive to negative connection but just between different batteries. what makes stops it shorting in this instance when the positive and negative of both batteries are identical. Im just not understanding. ☹️
All you have done by connecting the - side of one battery to the + of another identical, otherwise un-connected battery, is create one larger battery with twice the voltage potential across it. A standard 9V battery is simply constructed of six 1.5V batteries in series like this. Likewise, a standard car battery is six 2V cells connected in series.
Unless you connect something between the + and - terminals of this (now larger, higher voltage battery pack,) no current will flow through the open circuit. If you put a light bulb from the outer + to - terminals, electrons will flow out from the - terminal of the left battery in your diagram, through the light bulb and into the + of the right hand battery. An electrochemical reaction within the cells of the batteries provides the source of these electrons to be pushed/pulled through the now closed circuit.
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The key thing to understand is that electronics operate under a restricted subset of physical laws. Clearly you do not need a closed path for electricity to flow: rubbing a balloon on a fur coat will quickly disabuse you of this notion!
However, electronic circuits are somewhat simplified and the above example (where electrons "bunch up" in one place) is not allowed. The simplified laws allow for easier analysis. There are two main simplified models in electronics, called the Lumped Element model and the Transmission Line model. The Lumped Element model is introduced first and is easier to understand. It contains two classes of entities: Elements, such as resistors and capacitors; and Wires. Wires are assumed to be of zero impedance, as if they were perfect conductors. Elements are assumed to be located at a single point in space and only connected to the world through their attached Wires.
When the Lumped Element model is applied to your example of the two batteries, we notice something right away. Since charges are not allowed to bunch up anywhere in the circuit, each electron that wants to leave a battery through its (-) terminal needs to be replaced by another electron entering the battery at its (+) terminal. If there is nothing attached at the other terminal, they cannot move.
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You're asking a basic but valid question that is difficult to answer in some ways.
For the most part, in electronics, we think of voltage potential as relative.
In all cases really although in magneto dynamics the voltage is not easily defined.
Voltage potential can also be thought of in terms of absolutes. An isolated object with an equal number of positive and negative charges--protons and electrons--will have an absolute voltage of zero volts.
Not necessarily. It's still relative and there really is no absolute voltage. Sometimes it is useful to think of the "voltage at infinity" as zero but that still has no physical meaning. It is just a convenient convention. Even then isolated objects don't necessarily have zero potential except for boring definitions of isolated.
Voltage really is always relative. That is not an approximation or simplification is a fundamental fact of nature.
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Voltage really is always relative. That is not an approximation or simplification is a fundamental fact of nature.
I'm sorry, but that is absolutely :) not true. It is possible to define, quantify and measure the potential of an isolated object and that measurement is not relative to anything else. The usual definition of zero potential is when the charges are equal. Whether current will flow to or from another object is dependent on their relative potential, but there are other effects that only depend on the absolute charge difference. For example, if you charge up an object to a high enough absolute voltage, it can explode from the electrostatic repulsion of similar charges. That effect does not depend in any way on the presence or effect of another object or potential.
You can measure absolute voltage with one of these.
https://www.arborsci.com/products/demonstration-electroscope?variant=18112031195209&utm_medium=cpc&utm_source=google&utm_campaign=Google%20Shopping&gclid=CjwKCAjw2Jb7BRBHEiwAXTR4jfyo1IPxDsruewpqzHqaPzP1LB7kjvYdgtb744xl1Epc9rnExJJBlBoCxeAQAvD_BwE (https://www.arborsci.com/products/demonstration-electroscope?variant=18112031195209&utm_medium=cpc&utm_source=google&utm_campaign=Google%20Shopping&gclid=CjwKCAjw2Jb7BRBHEiwAXTR4jfyo1IPxDsruewpqzHqaPzP1LB7kjvYdgtb744xl1Epc9rnExJJBlBoCxeAQAvD_BwE)
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The key thing to understand is that electronics operate under a restricted subset of physical laws. Clearly you do not need a closed path for electricity to flow: rubbing a balloon on a fur coat will quickly disabuse you of this notion!
However, electronic circuits are somewhat simplified and the above example (where electrons "bunch up" in one place) is not allowed. The simplified laws allow for easier analysis. There are two main simplified models in electronics, called the Lumped Element model and the Transmission Line model. The Lumped Element model is introduced first and is easier to understand. It contains two classes of entities: Elements, such as resistors and capacitors; and Wires. Wires are assumed to be of zero impedance, as if they were perfect conductors. Elements are assumed to be located at a single point in space and only connected to the world through their attached Wires.
When the Lumped Element model is applied to your example of the two batteries, we notice something right away. Since charges are not allowed to bunch up anywhere in the circuit, each electron that wants to leave a battery through its (-) terminal needs to be replaced by another electron entering the battery at its (+) terminal. If there is nothing attached at the other terminal, they cannot move.
Thanks for posting this. I found it very helpful in connecting some "understanding dots". It might be a tad off topic or beyond topic regarding the OP's original question but still, it helped generate some insight. In looking up the definitions of lumped element vs transmission line I found that perhaps the compare and contrast might be better termed lumped element vs distributed element (or distributed system?) but that's maybe a terminology nit. (And no doubt we take our terminology pretty seriously so I am ready to be stand corrected....)
http://web.engr.oregonstate.edu/~traylor/ece391/Andreas_slides/ECE391-S14-Lect1-web.pdf (http://web.engr.oregonstate.edu/~traylor/ece391/Andreas_slides/ECE391-S14-Lect1-web.pdf)
Either way, the notion of "non-lumped" elements as "reflected" (haha) by transmission lines is for sure important (and fascinating).
https://www.allaboutcircuits.com/technical-articles/introduction-to-the-transmission-line/ (https://www.allaboutcircuits.com/technical-articles/introduction-to-the-transmission-line/)
What's a transmission line and why does it exist?
When the physical dimension of a circuit approaches the magnitude of a wavelength of the signal, wires and circuit traces begin to affect circuit performance. This is due to the effects being frequency dependent and typically having very small values that are linearly dependent on wire/trace length. When the frequency and lengths become comparably large, the impedance becomes non-negligible. The ratio of wavelength to wire length can be considered as low as 0.01.
As a mental shortcut, so as not having to analyze the harmonic components of a signal, compare the rise time of the signal to the propagation delay. If the rise time is less than twice the propagation delay, transmission line effects must be considered. So, for example, if the propagation delay of a wire or trace is 5ns, then any signal with a rise time of less than 10ns will be affected due to transmission line effects.
So again, apologies for taking the thread off-topic but thanks for stimulating the thoughts on the lumped model vs the distributed/transmission line/non-lumped model.
To the OP, I think your questions were focused in the realm of DC (and lumped models) vs AC (and distributed models with transmission lines) - and it's probably easier to figure out DC first and then move on to AC. In any event, keep asking your questions until things make sense. It is truly amazing how we can keep hearing the same words and discussing the same concepts and then one day someone says something with slightly different wording and stuff that didn't quite make sense snaps into sharper focus.
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You can think of it like this: there must be a circuit between the two terminals of any given cell in order for current to flow i.e. to get electrons flowing out of the negative terminal they must be able to return to the positive terminal on that same cell.
By only connecting the positive of one cell to the negative of the other, there is no path for electrons to flow back to their respective cells.
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Im still a bit confused guys, I do understand that you have to have a closed loop circuit for electricity in series thats not what Im asking. Its not a basic question i am trying to ask. What i am trying to ask, is why when touching the + to another battery - electricity doesn’t flow?
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The + of a battery is only + with respect to, or relative to, its own - end. It is not + or anything with respect to the other battery’s - end. I know that statement has some shortcomings but I think it’s superficially okay for the OPs original question.
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It might help if we take a look at the chemistry that makes a battery work: If you want to store electric energy you have to somehow separate charges: A capacitor is the simplest device that can separate charges: Two plates, you take the electrons from one plate and stick them onto the other plate. Can be used as a "battery", but it has one major problem: The voltage (aka how badly the electrons on the negative plate want to go to the positive plate) correlates linear to the electric charge (number of extra electrons on one plate): Half the charge, half the voltage. Not great if you want to power something that needs a fixed voltage.
A battery solves this problem by storing the charge electrochemically: It consists of two chambers (called half cells) that both have a metal electrode and a solution of the dissolved metal. Now, how do we get electrons flowing with this setup? We use two different metals (and solutions of dissolved metals), let's use Zinc/Zincsulfate and Copper/Coppersulfate as examples: One that badly wants to get rid of its electrons (Zinc) and one (dissolved metal) that wants those electrons (Coppersulfate) and connect the two metal electrodes. The metal that wants to get rid of its electrons (Zinc) dissolves and its electrons go to the other half cell: The dissolved metal there (in the form of Coppersulfate) (that badly wants electrons) takes them and gets deposited at the electrode in the form of elemental copper. Now we have another problem: The half cell with the metal that is dissolving (Zinc) is rapidly accumulating a positive charge as it is giving its electrons away while the half cell with the other metal (Copper) is building up a negative charge due to all the electrons it received. Nature really doesn't want such a buildup of charges (it wants chaos aka maximal entropy), so we have to get rid of the charges while still allowing electrons to flow. We do that by connecting two half cells with a membrane that only lets ions, but not electrons pass: The extra dissolved, positively charged Zinc goes to the Copper half cell while the negative sulfate ions from the copper half cell go the zinc half cell.
What happens when we connect two batteries the way you described? The electrons can flow, but we also need a flow of ions in the opposite direction to counter the buildup of positive and negative ions in the solutions. We have that between the two half cells in each battery, but not between the two batteries-> no ions can flow between them->no closed loop->no current flows
If a current was to flow we would get a buildup of positive charges in battery 1 due to the dissolving Zinc and a buildup of negative charges in battery 2 due to the copper getting electrons
If we take another cable and connect the other two terminals we get a current. Why? Because now we also get a buildup of charges in the other halfs of the batteries: The other half of battery 1 is building up a negative charge while the other half of battery 2 gets positive. But since ions can flow between the two halves of the batteries the charges get neutralized->current can flow.
Why do we use batteries if they are way more complicated than capacitors? Because their output voltages are fixed: You get 0.35 V if you give a dissolved Copper its electrons to become elemental copper and you get 0.76 V if your Zinc dissolves. Add those voltages and you get the voltage across your Copper/Zinc battery. That's also why we use Lithium in modern batteries: You get 3 V when it dissolves. Pair it with something that really wants electrons (like thionylchloride) and you get a cell voltage of 3.7 V.
(Yes, it's massively oversimplified, i know)
Edit: Added picture
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Im still a bit confused guys, I do understand that you have to have a closed loop circuit for electricity in series thats not what Im asking. Its not a basic question i am trying to ask. What i am trying to ask, is why when touching the + to another battery - electricity doesn’t flow?
I think the answers below helped persuade you that the loop is necessary, so now we get to your question about why it doesn't flow from battery to battery (even though it's clear there is no closed loop).
So, let's start by thinking about your first statement - that a closed loop is needed, and then compare that to your question (why doesn't it flow?)
It's a subtle thing no doubt, so here is one more way of trying to explain what is happening.
This is a Newton's Cradle:
https://en.wikipedia.org/wiki/Newton%27s_cradle#/media/File:Newtons_cradle_animation_book_2.gif
There is tendency to visualize an electron flowing around a circuit, but another way of visualizing it is to say that each electron bumps into the electron ahead if it. In order for each electron to bump the next electron, the next electron has to go somewhere (ie, bump into the next electron). If there is no path, ie no circuit that eventually allows for the continuation of the bumping process, there is an open loop or "open circuit", which by definition keeps the current from flowing. With no flowing current we can have "electrical potential" ie voltage, but we don't have flowing electricity ie, we have no current.
So, the answer keeps coming back as.....
IanB:
Electricity cares about going round in closed loops. If there is no loop, there is no flow.
When you join batteries end to end without completing the circuit there is no loop, therefore no flow can happen
ArthurDent:
Your drawing of the two batteries has no return path (it is open circuit) so there can be no current flow
drussell:
Unless you connect something between the + and - terminals of this (now larger, higher voltage battery pack,) no current will flow through the open circuit. If you put a light bulb from the outer + to - terminals, electrons will flow out from the - terminal of the left battery in your diagram, through the light bulb and into the + of the right hand battery. An electrochemical reaction within the cells of the batteries provides the source of these electrons to be pushed/pulled through the now closed circuit.
helius:
Since charges are not allowed to bunch up anywhere in the circuit, each electron that wants to leave a battery through its (-) terminal needs to be replaced by another electron entering the battery at its (+) terminal. If there is nothing attached at the other terminal, they cannot move.
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Im still a bit confused guys, I do understand that you have to have a closed loop circuit for electricity in series thats not what Im asking. Its not a basic question i am trying to ask. What i am trying to ask, is why when touching the + to another battery - electricity doesn’t flow?
Read my longer reply again. It DOES flow, at least in theory. Just not very much. It stops when the potential between the two terminals is equal.
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Im still a bit confused guys, I do understand that you have to have a closed loop circuit for electricity in series thats not what Im asking. Its not a basic question i am trying to ask. What i am trying to ask, is why when touching the + to another battery - electricity doesn’t flow?
How about you explain your reason for thinking electricity should flow when you connect it like that that instead of us repeating that a loop needs to exist?
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Im still a bit confused guys, I do understand that you have to have a closed loop circuit for electricity in series thats not what Im asking. Its not a basic question i am trying to ask. What i am trying to ask, is why when touching the + to another battery - electricity doesn’t flow?
How about you explain your reason for thinking electricity should flow when you connect it like that that instead of us repeating that a loop needs to exist?
:)
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Another try..... :)
Here is someone who asked a similar question - and the answers might or might not help.
https://electronics.stackexchange.com/questions/445525/when-you-connect-two-batteries-in-series-why-doesnt-the-middle-short/445535
But in this article there is a diagram showing that it would be possible to measure voltage and current in the two batteries touching configuration with the use of multimeters.
It might be interesting for the OP to do such measurements.... although that would not necessarily answer the question of why the values are shown by the measurements.
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Trying to "learn electricity" using a wire and batteries is like trying to "learn surgury" with a butcher knife.
In the next episode:
How can flat batteries still work?
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Im still a bit confused guys, I do understand that you have to have a closed loop circuit for electricity in series thats not what Im asking. Its not a basic question i am trying to ask. What i am trying to ask, is why when touching the + to another battery - electricity doesn’t flow?
You are assuming all positive terminals and all negative terminals are equivalent. They are not. You need to label the batteries #1 and #2 (first battery and second battery).
So, you can now label the terminals on the first battery as "Positive#1" and "Negative#1". You can label the other battery with "Positive#2" and "Negative#2".
Now, when you connect Positive#1 and Negative#1 with a wire, electricity can flow out of Positive#1, through the wire, into Negative#1, through the battery, and back to Positive#1. The through the battery bit is important. It is how the electricity gets back to the starting point (what closes the loop).
Draw this with a pencil on your diagram to be sure you understand it.
So let's try the same experiment with the two batteries. Electricity can flow out of Positive#1, through the wire, into Negative#2, through the second battery, out of Positive#2, and...then where? Where has the electricity got to go? There is no wire attached to Positive#2, so there is a dead end. There is no circuit. Therefore no electricity can flow.
Draw this again with your pencil on your drawing. How can you get back to home after you leave the positive terminal of the second battery?
If you want a different way to think about this, think about a motorway with traffic flowing along it. Suppose there is an accident and the carriageway is blocked? All the traffic comes to a standstill because it can't get past. All flow of traffic is stopped. The same is with electricity. If there is no path forward, the flow is blocked and everything comes to a standstill.
Someone earlier mentioned about static electricity with balloons and such. Guess why it is called "static" electricity? Static means stationary, not moving. Same thing. If electricity hasn't got a path to follow, it is stuck and doesn't move.
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The key thing to understand is that electronics operate under a restricted subset of physical laws. Clearly you do not need a closed path for electricity to flow: rubbing a balloon on a fur coat will quickly disabuse you of this notion!
However, electronic circuits are somewhat simplified and the above example (where electrons "bunch up" in one place) is not allowed. The simplified laws allow for easier analysis. There are two main simplified models in electronics, called the Lumped Element model and the Transmission Line model. The Lumped Element model is introduced first and is easier to understand. It contains two classes of entities: Elements, such as resistors and capacitors; and Wires. Wires are assumed to be of zero impedance, as if they were perfect conductors. Elements are assumed to be located at a single point in space and only connected to the world through their attached Wires.
When the Lumped Element model is applied to your example of the two batteries, we notice something right away. Since charges are not allowed to bunch up anywhere in the circuit, each electron that wants to leave a battery through its (-) terminal needs to be replaced by another electron entering the battery at its (+) terminal. If there is nothing attached at the other terminal, they cannot move.
Thanks for posting this. I found it very helpful in connecting some "understanding dots". It might be a tad off topic or beyond topic regarding the OP's original question but still, it helped generate some insight. In looking up the definitions of lumped element vs transmission line I found that perhaps the compare and contrast might be better termed lumped element vs distributed element (or distributed system?) but that's maybe a terminology nit. (And no doubt we take our terminology pretty seriously so I am ready to be stand corrected....)
Ahh, geez, guys, the poor kid was just trying to understand why two unconnected cells/batteries don't short out across thin air.... :)
Do we need to get into lumped element vs distributed element analysis in a beginner's thread? ;D
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I'm more interested in knowing how the OP's misconception came about. I suspect it's through interpreting very literally the "rule" that current flows from + to -. :popcorn:
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Im still a bit confused guys .... .... ....
What i am trying to ask, is why when touching the + to another battery - electricity doesn’t flow?
Hi challie2!
When it comes to these very basic questions of understanding, you will gets lots of replies that are accurate - but are not helping you understand. This is, perhaps, one of the greatest challenges of the newcomer - wading through it all. (In fact, there's a graphic somewhere which has been used before - I'll dig it up ...)
I suggest you read THIS reply and pay close attention as it is the only one I've read so far that clearly and succinctly makes the point you need to understand....
The + of a battery is only + with respect to, or relative to, its own - end. It is not + or anything with respect to the other battery’s - end.
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Here's the graphic I mentioned....
(https://www.eevblog.com/forum/beginners/beginners-don_t-run-away-please!/?action=dlattach;attach=399689;image)
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The key thing to understand is that electronics operate under a restricted subset of physical laws. Clearly you do not need a closed path for electricity to flow: rubbing a balloon on a fur coat will quickly disabuse you of this notion!
However, electronic circuits are somewhat simplified and the above example (where electrons "bunch up" in one place) is not allowed. The simplified laws allow for easier analysis. There are two main simplified models in electronics, called the Lumped Element model and the Transmission Line model. The Lumped Element model is introduced first and is easier to understand. It contains two classes of entities: Elements, such as resistors and capacitors; and Wires. Wires are assumed to be of zero impedance, as if they were perfect conductors. Elements are assumed to be located at a single point in space and only connected to the world through their attached Wires.
When the Lumped Element model is applied to your example of the two batteries, we notice something right away. Since charges are not allowed to bunch up anywhere in the circuit, each electron that wants to leave a battery through its (-) terminal needs to be replaced by another electron entering the battery at its (+) terminal. If there is nothing attached at the other terminal, they cannot move.
Thanks for posting this. I found it very helpful in connecting some "understanding dots". It might be a tad off topic or beyond topic regarding the OP's original question but still, it helped generate some insight. In looking up the definitions of lumped element vs transmission line I found that perhaps the compare and contrast might be better termed lumped element vs distributed element (or distributed system?) but that's maybe a terminology nit. (And no doubt we take our terminology pretty seriously so I am ready to be stand corrected....)
Ahh, geez, guys, the poor kid was just trying to understand why two unconnected cells/batteries don't short out across thin air.... :)
Do we need to get into lumped element vs distributed element analysis in a beginner's thread? ;D
Point well taken. :-+
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Here's the graphic I mentioned....
(https://www.eevblog.com/forum/beginners/beginners-don_t-run-away-please!/?action=dlattach;attach=399689;image)
challie2, this is great advice. Give us your next question....
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I tried to go with as simple an explanation as I could . When you look at a battery . The positive side is not positively charged but has a lower negative potential than the negative side . I used your picture to give an explanation.
Sorry about the lopsided picture.
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I'm sorry, but that is absolutely :) not true. It is possible to define, quantify and measure the potential of an isolated object and that measurement is not relative to anything else. The usual definition of zero potential is when the charges are equal. Whether current will flow to or from another object is dependent on their relative potential, but there are other effects that only depend on the absolute charge difference. For example, if you charge up an object to a high enough absolute voltage, it can explode from the electrostatic repulsion of similar charges. That effect does not depend in any way on the presence or effect of another object or potential.
You are confusing charge with voltage. Charge causes voltage but they aren't the same thing. There are no effects whatsoever that depend on absolute voltage. An object with high net charge will indeed experience repulsion between those charges, independent of the voltage. I 100% promise you that there is no meaning or measurable effect of absolute voltage. Charges respond to electric fields. Electric field is the gradient of voltage. Adding a constant voltage offset doesn't change the gradient, therefore doesn't change the electric field, and has no effect on any measurable force. You can hide the reference terminal, but you can't eliminate it.
You can measure absolute voltage with one of these.
https://www.arborsci.com/products/demonstration-electroscope?variant=18112031195209&utm_medium=cpc&utm_source=google&utm_campaign=Google%20Shopping&gclid=CjwKCAjw2Jb7BRBHEiwAXTR4jfyo1IPxDsruewpqzHqaPzP1LB7kjvYdgtb744xl1Epc9rnExJJBlBoCxeAQAvD_BwE (https://www.arborsci.com/products/demonstration-electroscope?variant=18112031195209&utm_medium=cpc&utm_source=google&utm_campaign=Google%20Shopping&gclid=CjwKCAjw2Jb7BRBHEiwAXTR4jfyo1IPxDsruewpqzHqaPzP1LB7kjvYdgtb744xl1Epc9rnExJJBlBoCxeAQAvD_BwE)
That measures the charge on the plate, not any "absolute" voltage which again -- is not a real thing. You can see this by a simple example: take your electroscope and charge up the plate so that the needle moves. Then attach a battery or power supply to the base plate. As you adjust that power supply the voltage of the entire system will be shifted relative to the power supply ground but the needle won't move. That's because the charge on the plate won't change.
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Its not a basic question i am trying to ask. What i am trying to ask, is why when touching the + to another battery - electricity doesn’t flow?
If you're trying look under the hood, then you're come to AC world. The answer on your question - it flows. When you connect (-) terminal of first battery with (+) terminal of second battery, the electric current is really flows. But it flows for very-very short period of time, so you even cannot notice it. It just stops to flow in a short period of time, because there is no path to flow.
The same thing happens when you connect water pump to a pipe with closed output on the other pipe end. At the first moment water flows from pump into pipe. But since there is no output from pipe, the pressure quickly raise and this pressure produces a counteracting to the pump.
The same thing happens in the wire with electron gas. When you connect wire to (+) terminal of the second battery, electron gas flows from the first battery to the second battery. But since there is no output from (-) terminal on the second battery, it leads to higher density of electron gas and it starts to flow back to the first battery. This is known as wave reflection. And this is what is described in Transmission Line theory.
Actually electrons don't sit at the same location, it always move at random direction. But when there is no way to move, it just move back and forth at random directions. And in average there is no movement. These random back and forth movement of electrons is everywhere. It is known as thermal noise. You can hear this electrons movement with amplifier, for example you can listen it with a good radio receiver :)
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@challie2:
When the other guys say you need a "loop" that means you need some sort of CIRCLE (hence "circuit"). If you just connect two batteries like this:
[PLUS1-MINUS1]---[PLUS2-MINUS2]
there is no circle. Yes, there is a *connection* between MINUS1 and PLUS2, but this connection does not form a circle.
Some words specific to batteries: a battery works by means of a chemical reaction that moves electrons from MINUS to PLUS. For this movement, some sort of bridge must be created between the terminals. The electronics do not move within the battery itself from MINUS to PLUS (otherwise, there would be short within the battery and you couldn't use it for anything).
If you create the series connection as above, the terminals of the individual batteries 1 and 2 are not bridged (that means, there is no connection from MINUS1 to PLUS1 and no connection from MINUS2 to PLUS2), so no chemical reaction can take place that moves electrons from MINUS1 to PLUS1 or from MINUS2 to PLUS2. You think that they should move from MINUS1 to PLUS2, but between those terminals, there is no battery, so no chemical reaction can take place to move the electrons.
The only places here where chemical reactions can take place is within battery 1 and battery 2, and those reactions "want" to move electrons from MINUS1 to PLUS1 and from MINUS2 to PLUS2. The series connection above only supports those reactions if the circle is closed, not when it is open.
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You think that they should move from MINUS1 to PLUS2, but between those terminals, there is no battery, so no chemical reaction can take place to move the electrons.
Actually they always move. And electric current will flows from MINUS1 to PLUS2, but since there is no path to continue flow, it will be reflected back from PLUS2 terminal and flow back to MINUS1.
So, when you attach MINUS1 to PLUS2 you will see electric current something like this:
(https://i.imgur.com/JAgy6ap.png)
But the frequency of this bouncing will be very high, because electricity is really fast :) So your voltmeter cannot measure it, because current drops to zero at very-very short period of time.
If you want to catch such current of open circuit, you can try to use very long coaxial cable with open end. Since wave propagation in coax cable is about 197'863 kilometers per second, you can measure current between battery and cable before pulse reach to the end of cable and returns back to the battery. You will see a short pulse of current when you attach long cable to the battery. :)
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Its not a basic question i am trying to ask. What i am trying to ask, is why when touching the + to another battery - electricity doesn’t flow?
If you're trying look under the hood, then you're come to AC world. The answer on your question - it flows. When you connect (-) terminal of first battery with (+) terminal of second battery, the electric current is really flows. But it flows for very-very short period of time, so you even cannot notice it. It just stops to flow in a short period of time, because there is no path to flow.
The same thing happens when you connect water pump to a pipe with closed output on the other pipe end. At the first moment water flows from pump into pipe. But since there is no output from pipe, the pressure quickly raise and this pressure produces a counteracting to the pump.
The same thing happens in the wire with electron gas. When you connect wire to (+) terminal of the second battery, electron gas flows from the first battery to the second battery. But since there is no output from (-) terminal on the second battery, it leads to higher density of electron gas and it starts to flow back to the first battery. This is known as wave reflection. And this is what is described in Transmission Line theory.
Actually electrons don't sit at the same location, it always move at random direction. But when there is no way to move, it just move back and forth at random directions. And in average there is no movement. These random back and forth movement of electrons is everywhere. It is known as thermal noise. You can hear this electrons movement with amplifier, for example you can listen it with a good radio receiver :)
You think that they should move from MINUS1 to PLUS2, but between those terminals, there is no battery, so no chemical reaction can take place to move the electrons.
Actually they always move. And electric current will flows from MINUS1 to PLUS2, but since there is no path to continue flow, it will be reflected back from PLUS2 terminal and flow back to MINUS1.
So, when you attach MINUS1 to PLUS2 you will see electric current something like this:
(https://i.imgur.com/JAgy6ap.png)
But the frequency of this bouncing will be very high, because electricity is really fast :) So your voltmeter cannot measure it, because current drops to zero at very-very short period of time. :)
If you want to catch such current of open circuit, you can try to use very long coaxial cable with open end. Since wave propagation in coax cable is about 197'863 kilometers per second, you can measure current between battery and cable before pulse reach to the end of cable and returns back to the battery. You will see a short pulse of current when you attach long cable to the battery. :)
All of this is completely unhelpful to furthering the OP's understanding, just potentially adding more confusion.
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Voltage really is always relative. That is not an approximation or simplification is a fundamental fact of nature.
I'm sorry, but that is absolutely :) not true. It is possible to define, quantify and measure the potential of an isolated object and that measurement is not relative to anything else. The usual definition of zero potential is when the charges are equal. Whether current will flow to or from another object is dependent on their relative potential, but there are other effects that only depend on the absolute charge difference. For example, if you charge up an object to a high enough absolute voltage, it can explode from the electrostatic repulsion of similar charges. That effect does not depend in any way on the presence or effect of another object or potential.
You can measure absolute voltage with one of these.
https://www.arborsci.com/products/demonstration-electroscope?variant=18112031195209&utm_medium=cpc&utm_source=google&utm_campaign=Google%20Shopping&gclid=CjwKCAjw2Jb7BRBHEiwAXTR4jfyo1IPxDsruewpqzHqaPzP1LB7kjvYdgtb744xl1Epc9rnExJJBlBoCxeAQAvD_BwE (https://www.arborsci.com/products/demonstration-electroscope?variant=18112031195209&utm_medium=cpc&utm_source=google&utm_campaign=Google%20Shopping&gclid=CjwKCAjw2Jb7BRBHEiwAXTR4jfyo1IPxDsruewpqzHqaPzP1LB7kjvYdgtb744xl1Epc9rnExJJBlBoCxeAQAvD_BwE)
Again, not helpful to the OP's understanding. And while it may be true (dubious) from a pure physics standpoint that voltage can be absolute, the electronics in question here clearly and unambiguously deals only with current electricity (http://www.differencebetween.net/science/difference-between-current-and-static-electricity/), where voltage is definitely a relative measurement. Bringing electroscopes into the picture for someone who clearly needs to be learning the basics of a multimeter is simply not helpful.
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But this is completely unhelpful to furthering the OP's understanding, just potentially adding more confusion.
I couldn't agree more.
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But this is completely unhelpful to furthering the OP's understanding, just potentially adding more confusion.
He said that he want to know why there is no current. I think he understand that it needs circuit for current flow, but he want to understand why current is missing when there is circuit break.
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He said that he want to know why there is no current. I think he understand that it needs circuit for current, but he want to understand why current is missing when there is break.
that doesn't make any sense. if i have understood that I need a circle, then i don't need to ask why there is no current without a circle. please let us stop this wankery and concentrate on helping the op.
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that doesn't make any sense. if i have understood that I need a circle, then i don't need to ask why there is no current without a circle. please let us stop this wankery and concentrate on helping the op.
He may know that there is need a closed electrical circuit for a current flow just because someone said that. But it doesn't means that he understand why
Anyway, after so many comments, I think now he should understand it. So, let's wait what he says :)
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All of this is completely unhelpful to furthering the OP's understanding, just potentially adding more confusion.
This thread is like when a young child asks where do babies come from and they end up getting a lecture on obstetrics and gynaecology and who knows what else, when they would be satisfied with the answer "mummy's tummy."
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in my post above I have tried to make it as simple and concise as possible, but this attempt gets sabotaged basically immediately. I think in this forum there is a lack of rules how to behave in threads like this.
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in my post above I have tried to make it as simple and concise as possible, but this attempt gets sabotaged basically immediately. I think in this forum there is a lack of rules how to behave in threads like this.
your answer, which you're talking about, is that there is need a closed loop circuit and what it means.
But just look what topic starter wrote before your answer:
Im still a bit confused guys, I do understand that you have to have a closed loop circuit for electricity in series thats not what Im asking. Its not a basic question i am trying to ask. What i am trying to ask, is why when touching the + to another battery - electricity doesn’t flow?
This is pretty obvious, that the topic starter claims that he know, that there is need a closed loop. But he asking why current don't flows.
But after that you're trying to explain that there is need closed loop and what it means.
And you wrote that he don't need answer why:
He said that he want to know why there is no current. I think he understand that it needs circuit for current, but he want to understand why current is missing when there is break.
that doesn't make any sense. if i have understood that I need a circle, then i don't need to ask why there is no current without a circle. please let us stop this wankery and concentrate on helping the op.
As you can see, your answer is not what topic starter asked for.
You're trying to say that the answer on topic starter question "why" doesn't make any sense, because if he know about closed loop, then he "don't need to ask why"...
But topic starter clearly stated that he needs answer "why".
And he clearly stated that he already knows that there is needs closed loop.
So who attempts to sabotage? :)
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for the two batteries, connect the other positive to the other negative and you will have a closed loop and current will flow.
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another example of current flow with no closed loop is a capacitor. There is no connection between capacitor terminals. But if you apply battery to the capacitor, you will see a short pulse of current. After some period of time needed to charge capacitor, current will drops to zero.
The same thing happens when you connect terminals MINUS1 and PLUS2, but since capacitance is much lower, it will happens much-much faster :)
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You are confusing charge with voltage.
No, really, I"m not. I was only providing a simple explanation that I thought the OP might understand, not a complete grade-school class on electrostatics, but to simply refute your assertion:
1. Charge is measured in Coulombs.
2. Potential, aka voltage, is defined in terms of the work required (+ or -) to move a unit charge from one state or object to another. This holds for any type of voltage, whether it be a 9V battery or a balloon. What I call 'absolute' voltage is the work required to move a unit charge from infinity to the charged object.
3. Charge and potential are related to each other and as far as single, isolated objects go, that relationship is called Capacitance.
That measures the charge on the plate, not any "absolute" voltage which again -- is not a real thing. You can see this by a simple example: take your electroscope and charge up the plate so that the needle moves. Then attach a battery or power supply to the base plate. As you adjust that power supply the voltage of the entire system will be shifted relative to the power supply ground but the needle won't move. That's because the charge on the plate won't change.
I'm assuming your power supply is grounded to earth on the other end. The balanced-pointer electroscope ideally responds to its own charge and not external electric fields because external fields will act on both sides of the pointer uniformly. With foil-type indicators your experiment might actually cause some change if the power supply were strong enough. I don't have any idea what you mean when you say the voltage of the entire system will be shifted--two isolated objects that you define as a 'system' don't have one single potential. The base plate is insulated from the indicator so no charge is transferred. The indicator doesn't move because it is responding to its own 'absolute' voltage potential, not any external field.
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Again, not helpful to the OP's understanding. And while it may be true (dubious) from a pure physics standpoint that voltage can be absolute, the electronics in question here clearly and unambiguously deals only with current electricity (http://www.differencebetween.net/science/difference-between-current-and-static-electricity/), where voltage is definitely a relative measurement. Bringing electroscopes into the picture for someone who clearly needs to be learning the basics of a multimeter is simply not helpful.
I have found that when someone asks a question that appears to be the 'wrong' question, the best course is to at least try to address the actual question before proceeding on to tell the querier that they 'should' be asking a different question. I wouldn't presume anything about the OPs intentions nor what they should or should not be learning.
Electricity in the cosmos is largely of the static and absolute variety, not the sideshow we call electronics where we 'tame' it and make it run around in loops and through our devices like a flea circus.
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While it is true that once connected together, electrons are now able to flow between the two batteries connected via one battery's - terminal to the other's + terminal with no second connection (and in the strictest physics sense a few do flow momentarily,) I think that the OP still needs to grasp the more fundamental idea that with nothing to push those electrons "out" the - side or attract them, suck them "in the other side", the + side of the far battery by actually having somewhere to go, no current will flow through the (open) circuit.
Once the circuit is closed, the electrons are pushed and pulled through the circuit "loop", causing current to flow.
How much current flows depends on the voltage (ie. pressure) and how well connected everything is. (The resistance of the circuit.)
While yes, from a strictly technical physics perspective this is a simplification, I don't think it is probably helpful to the OP's basic understanding to get into transmission lines and watching electrons zip through long coaxial cables to show that a yes, few electrons do actually zip along to balance any two electrically connected things out, but I don't think that was what the OP was getting at. I could be wrong, though, of course, we'll have to let the OP chime in. :)
There are better ways of demonstrating that principle, like using a Van de Graaff generator to make static electricity build up a bunch of electrons on one person, making their hair stand up, then joining another person, or using balloons with bits of styrofoam or whatever and showing that half of the charge moves to another balloon by seeing how the styrofoam bits behave when you "connect" the balloons so the electrons can jump over and even out between the two balloons, etc. etc.
Edit: Changed wording in first paragraph to try to be more clear.
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Electricity in the cosmos is largely of the static and absolute variety, not the sideshow we call electronics where we 'tame' it and make it run around in loops and through our devices like a flea circus.
Indeed.
Electronics is all about taming some of those wild, "angry pixies" and forcing them to do work for us. :)
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Again, not helpful to the OP's understanding. And while it may be true (dubious) from a pure physics standpoint that voltage can be absolute, the electronics in question here clearly and unambiguously deals only with current electricity (http://www.differencebetween.net/science/difference-between-current-and-static-electricity/), where voltage is definitely a relative measurement. Bringing electroscopes into the picture for someone who clearly needs to be learning the basics of a multimeter is simply not helpful.
I have found that when someone asks a question that appears to be the 'wrong' question, the best course is to at least try to address the actual question before proceeding on to tell the querier that they 'should' be asking a different question. I wouldn't presume anything about the OPs intentions nor what they should or should not be learning.
Electricity in the cosmos is largely of the static and absolute variety, not the sideshow we call electronics where we 'tame' it and make it run around in loops and through our devices like a flea circus.
Maybe the OP is snoozing, or enjoying what the question unleashed with some :popcorn: , or getting some really good :-DD ‘s out of this, or is trying to take it all in but is finding it |O . Seems at least temporarily MIA.... who knows....? But in the meantime this thread is informative , entertaining, and I think maybe going to be pretty memorable. This might deserve to be in a sticky of good quotes:
”Electricity in the cosmos is largely of the static and absolute variety, not the sideshow we call electronics where we 'tame' it and make it run around in loops and through our devices like a flea circus.”
- emphasis on the italic part :) :-+
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Again, not helpful to the OP's understanding. And while it may be true (dubious) from a pure physics standpoint that voltage can be absolute, the electronics in question here clearly and unambiguously deals only with current electricity (http://www.differencebetween.net/science/difference-between-current-and-static-electricity/), where voltage is definitely a relative measurement. Bringing electroscopes into the picture for someone who clearly needs to be learning the basics of a multimeter is simply not helpful.
I have found that when someone asks a question that appears to be the 'wrong' question, the best course is to at least try to address the actual question before proceeding on to tell the querier that they 'should' be asking a different question.
I didn't tell the querier what they should be asking. I was admonishing responders to keep the replies at a level appropriate for the querier. Going off on know-it-all tangents that are way beyond the OP's head is nothing more than posturing.
I wouldn't presume anything about the OPs intentions nor what they should or should not be learning.
I didn't make any such presumptions. My analogy about the multimeter was at you for bringing electrometers into the discussion!
Electricity in the cosmos is largely of the static and absolute variety, not the sideshow we call electronics where we 'tame' it and make it run around in loops and through our devices like a flea circus.
OK, I must grant you that that's a magnificent wording! But with that said, in reality, we constantly use abstractions and simplifications, because it's literally impossible to learn everything at full detail from the beginning. That's why we start by teaching rules, and then later, we say "so remember that rule from before? OK, it was actually a lie, there are exceptions." And we iteratively repeat this, because starting with simplifications is the way to get the big picture, which is needed in order to make sense of the details.
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I didn't make any such presumptions. My analogy about the multimeter was at you for bringing electrometers into the discussion!
Yes, a bit of thread creep. That was directed at ejeffrey, not the OP. But on reflection, perhaps the beginner-level explanations should start with basic demonstrations of electrostatics and not defer that to a college-level course on electric fields. I happen to like the historical method of teaching science, where you learn about things roughly in the order that they were discovered. I suppose todays crop of young would die of boredom doing it that way.
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Maybe the OP is snoozing, or enjoying what the question unleashed with some :popcorn: , or getting some really good :-DD ‘s out of this, or is trying to take it all in but is finding it |O .
This thread does seem to be a bit out of step with his posting history. :popcorn:
https://www.eevblog.com/forum/profile/?area=showposts;u=124265 (https://www.eevblog.com/forum/profile/?area=showposts;u=124265)
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I didn't tell the querier what they should be asking. I was admonishing responders to keep the replies at a level appropriate for the querier. Going off on know-it-all tangents that are way beyond the OP's head is nothing more than posturing.
The topic starter clearly state that he already know about closed loop circuit and this is not what he asking. He clearly state that he don't need a basic information, because he already know that. He asked to explain why current don't flows at more detailed level.
just look what topic starter wrote:
Im still a bit confused guys, I do understand that you have to have a closed loop circuit for electricity in series thats not what Im asking. Its not a basic question i am trying to ask.
Did you seen that?
So, why you're still trying to give basic answer for topic starter?
He said that he already know that and don't need basic answer. Isn't it? :)
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The first few replies in this topic gave the answer to the question for those without a physics degree and some of the other replies just confuse what is a simple question with a simple answer suited for the beginning section. Just think about all the examples of ‘cells’ in series we have in real life.
A 2 cell flashlight (diagram below) uses 2 cells in series to deliver twice the voltage of 1 cell to the bulb. It is the switch that, when closed, allows the circuit to be completed through the bulb and the bulb lights as current flows. If the switch is open there is no complete circuit, no current flows, and no light even though there is a physical connection between the 2 batteries just like in the original drawing.
A 12 volt auto battery is another example where you actually have six 2 volt cells in series in one case and connecting the cells in series does not cause the cells to discharge. Only when this 6 cell battery is connected to the car and various loads are connected (radio, wipers, headlights) does current flow.
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I didn't tell the querier what they should be asking. I was admonishing responders to keep the replies at a level appropriate for the querier. Going off on know-it-all tangents that are way beyond the OP's head is nothing more than posturing.
The topic starter clearly state that he already know about closed loop circuit and this is not what he asking. He clearly state that he don't need a basic information, because he already know that. He asked to explain why current don't flows at more detailed level.
just look what topic starter wrote:
Im still a bit confused guys, I do understand that you have to have a closed loop circuit for electricity in series thats not what Im asking. Its not a basic question i am trying to ask.
Did you seen that?
So, why you're still trying to give basic answer for topic starter?
He said that he already know that and don't need basic answer. Isn't it? :)
Because the OP's original question clearly shows some severe confusion at a more basic level.