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As I know a battery is an example of a closed circuit where it can then produce electricity , electrons will flow from negative pole to positive. A chemistry representation of this battery is for example I got this link : http://www.youtube.com/watch?v=0TvYlJ06MXo&feature=related

So it's a closed circuit where one of the side will release (lose) electron while another side will gain electrons. That's how the circular process will occur (the liquid act as a connector or bridge to close the circuit). What if we 'open' the circuit , so i mean separate the liquid?

Of course the chain process will stop, right? But what about if we can create some kind of instrument where I can supply electron to the liquid and on the other side using another tool/instrument to grab electrons from another liquid. Does it make any sense, that we can still produce electricity using open circuit? Am i wrong?

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A battery is basically just a chemical reaction. At the negative (cathode) end of the battery the reaction releases electrons while at the positive (anode) end of the battery the reaction consumes electrons. As long as the external circuit allows electrons to flow from the cathode to the anode the reaction goes and the battery generates power.

If you break the external circuit then electrons can't flow and the battery stops producing power. But if you can use some kind of instrument (to use your words) to supply electrons to the anode and remove them from the cathode the reaction in the battery will go and the battery will produce power. The battery doesn't care where the electrons are coming from or where they're going.

But you won't be able to do this indefinitely because as you remove electrons from the cathode you end up with a large collection of electrons i.e. a negative charge. In the same way, as you supply electrons to the anode you'll end up with a positive charge. This charge separation generates a potential difference (i.e. a voltage) and as soon as this voltage gets bigger than the battery voltage the electrons will stop flowing. At this point you'll need to let the two collections of charges neutralise by closing the external circuit or the battery will stop producing power.

An extreme example of the open circuit is the battery itself. If you pick up a battery it will have an excess of electrons at the -ve end and a deficit of electrons at the +ve end because the battery has pushed electrons to its ends until it couldn't push any more.

Response to comment:

Circuits

A very common analogy for an electrical circuit is to image it as a series of pipes with water flowing through them. The electrons are analagous to the water, and the battery is the water pump. So the usual closed circuit is shown on the left, with the battery pumping water (electrons!) out of one end of the battery, round the circuit and back in the other end of the battery.

The open circuit is represented by the diagram on the right, where the battery pumps water up from a closed container at the bottom to another closed container at the top. As the battery pumps water the pressure in the bottom decreases and the pressure at the top increases, and at some point the pressure difference will get bigger than the pump can manage. You can use a more powerful pump (i.e. a higher voltage) but even this will reach a point where it can't pump any more water.

This is why a battery in an open circuit can only pump a certain amount of electrons. As it pumps electrons they generate a reverse voltage that opposes the battery.

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  • $\begingroup$ sorry i don't understand when you said '..and as soon as this voltage gets bigger than the battery voltage the electrons will stop flowing.' , i think the highest the voltage or potential difference then the bigger current will flow. Am i right ? and also there is no battery voltage yet. Whatever voltage it is , it become the battery voltage. $\endgroup$
    – andio
    Commented Nov 28, 2012 at 12:06
  • $\begingroup$ @andio - I've edited my answer to (I hope!) make things clearer. $\endgroup$
    – John Rennie
    Commented Nov 28, 2012 at 12:32
  • $\begingroup$ Awesome!! That's explain very well. This is what i was thinking previously : according to your right-side pic (open circuit), the electron can't flow continuously…. actually they can if both ends are connected to some kind of intruments/tools to supply and to remove electron continuously. We can describe this instrument as black box as i don't know how it produces/adsorb electron. But then another question how can this black box keep supplying or adsorbing electron indefinitely ? (continue) $\endgroup$
    – andio
    Commented Nov 28, 2012 at 13:21
  • $\begingroup$ there will be a lot of electron stagnancy. IT must need a hugh energy to deal with that. well it needs another black boxes … then everything start to be indefinitely unsolved .. which one come first ? chicken or egg. At the end like you said it needs to be NEUTRALIZED or BALANCED (this is the key)so the next process can occur. In the other word , the two black box need to connect each other (salt bridge). So this way, they can 'cure' each other as a complete closed chain reaction. Nice explanation Sir. Thanks a lot for sharing your thought. $\endgroup$
    – andio
    Commented Nov 28, 2012 at 13:21
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    $\begingroup$ In theory if I use Anode from one battery and Cathode from different battery (those batteries are NOT connected on another side) I will get the voltage difference, So it will be open circuit But current will flow through the line. Right? $\endgroup$
    – Irakli
    Commented Nov 8, 2013 at 19:56
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The answer is YES, it is possible for current to flow in an open circuit. The only requirement is that the current be "alternating" current. A capacitor is essentially an open circuit, and alternating current will "flow" trough it.

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  • $\begingroup$ I often wonder how an isolating transformer can even work. If I grab one end, there would be a 120V AC potential in my body. If I'm standing in a puddle on the ground, how is the ground going to just ignore the voltage differential? $\endgroup$
    – Brain2000
    Commented Jul 11, 2017 at 3:48
  • $\begingroup$ Since the transformer is isolated, the ground will force the one transformer output to 0V, and the transformer won't care. It only cares about the difference between the outputs, so to speak. $\endgroup$
    – avl_sweden
    Commented Nov 28, 2017 at 9:02
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This isn't what you're asking, but it is possible for currents to flow in an open circuit. Even a plain old block of copper is an "open circuit", for instance, but you can induce eddy currents to flow in it by applying a changing magnetic field. In a regular circuit this effect would be very small, though, as the copper wires have small width.

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Spark plugs are an open circuit. But there is an exceptional amount of voltage causing a spark to jump the gap, same as lighting.

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    $\begingroup$ A true fact, but wrong interpretation. When a spark is created, there is no more “gap” and the circuit becomes closed with a new element: gas-discharging resistor. $\endgroup$
    – Incnis Mrsi
    Commented Oct 24, 2014 at 9:55

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