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My textbooks at the moment don't really explain the underlying theory of circuits. All I do is apply the rules I was taught when I solve these problems. I don't get why electrons need to have a closed loop in order to want to flow.

The circuit I'm analysing right now is an RC circuit. The battery in the circuit is removed after the capacitor is fully charged, when the interruptor is closed for some reason electrons want to flow. Why is this? And how are they doing it?

Thanks a lot.

DLV
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2 Answers2

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Your question has two parts.

First addressing why electron needs a closed loop to flow-

Consider a wire which is not closed for e.g in the diagram. Here Due to the electric field(marked in green) the electrons move to the right.But after some time the electrons accumulate in the right forms their own electric field with the positive charge(marked in red).As a result both Electric fields cancel together and current stops flowing.Tragic...enter image description here

But this does not occur in closed loops which helps to maintain the current.

Addressing the second part of your question

The battery in the circuit is removed after the capacitor is fully charged, when the interruptor is closed for some reason electrons want to flow.

After the capacitor is fully charged,a potential difference is established between the two plates and obviously electron wants to flow by some path or the other-their target is to do work by the potential energy they have.As the electric field is conservative the path does not matter.Now,how will they flow if wire is not closed??So as soon as the wire is closed they start to flow due to the potential difference.

soumyadeep
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  • I've seen the first part of your explanation elsewhere but I don't understand why this doesn't happen in a closed loop. As for the second part of your answer, I don't see why they couldn't flow if the wire wasn't closed. Is this because of the first part of your answer? Thanks :( – DLV Oct 08 '14 at 16:34
  • In a closed loop the electron comes out of the battery and flows inside it.So it has no oppurtinity to accumulate and create an opposing electric field. – soumyadeep Oct 08 '14 at 16:37
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    As of the second part,describe the path you think that the electron might flow if loop is not closed.and even if you find a path,yes the first part is the answer. – soumyadeep Oct 08 '14 at 16:39
  • Can I post a picture that's in my textbook along with a quick question and you add it as part of your answer? It's related to the direction of the current as the capacitor is discharged – DLV Oct 08 '14 at 16:42
  • Sure its a free world;).... – soumyadeep Oct 08 '14 at 16:43
  • i've posted the image. you can ignore the spanish, although you might probably imagine what it is they're saying. – DLV Oct 08 '14 at 16:50
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    Well i am sorry i didnt realise it would be this long.Do one thing cut this from this question and post another question or else your question will be put on hold with the tag of "too broad" – soumyadeep Oct 08 '14 at 16:52
  • http://physics.stackexchange.com/questions/139388/why-have-they-chosen-this-direction-for-current-in-the-rc-circuit-seems-pretty Thats the link to my new Q. – DLV Oct 08 '14 at 16:55
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Why does current need a closed loop to flow? Not in every case you need a closed circuit.

A good example that current in an open "circuit" can flow is the antenna rod. A generator generates an alternating current and the electrons in the rod moves and there is an electric flow.

HolgerFiedler
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