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Electric Current in an open circuit

  1. Dec 27, 2013 #1
    I'm still a beginner at Electricity and electromagnetism, I'm wondering If we connect a wire to a positive terminal ONLY , why won't the electrons flow to the positive terminal of the cell as electrons are negatively charged, I have been days thinking about it and I need a clear convincing answer I don't matter if it is in detail but I need an understandable answer for a beginner
     
  2. jcsd
  3. Dec 27, 2013 #2

    TumblingDice

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    Why wouldn't they? (as long as there's nothing wrong with the wire)
     
  4. Dec 27, 2013 #3
    So there would be an instantaneous current in the wire?
     
  5. Dec 28, 2013 #4

    Student100

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    In chemical batteries the electrolyte prevents electrons from going up from the anode to the cathode. It would be kind of pointless to have a battery that constantly was reacting without a circuit.

    Well hopefully they wouldn't, seeing as how he hasn't completed the circuit.
     
  6. Dec 28, 2013 #5
    But the electrons would move towards the anode the they would stop? I mean some kind of an instantaneous current
     
  7. Dec 28, 2013 #6
    Then they would stop *********
     
  8. Dec 28, 2013 #7

    Student100

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    Current flows from the anode to the cathode, a wire connected on the cathode only wouldn't permit the chemical reaction to occur. As I said before, the electrolyte prevents stray elections from going anode -> cathode.

    This is an over simplistic view on batteries in general, but I’m not sure how much you actually understand.

    So no, no instantaneous or inrush current that I’m aware of, but I have a very superficial understanding of batteries in general.
     
  9. Dec 28, 2013 #8

    I'm talking about a wire connected to the anode not to the cathode
     
  10. Dec 28, 2013 #9

    Student100

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    Then edit your question, the anode is the negative terminal.
     
  11. Dec 28, 2013 #10
    I'm a little bit confused I'm so sorry, I know the fact that chemical reactions won't occur in an open circuit but I mean why won't the electrons move toward the cathode "as electrons are negatively charged" then just stop there till the circuit is closed
     
  12. Dec 28, 2013 #11

    Student100

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    Like I said, there is “stuff”(electrolyte) inside the battery that prevents electrons from moving inside the battery itself.

    If you just had a wire on either the anode or cathode you have an open circuit. V=I/R, which means voltage equals current divided by resistance, think about the resistance of air for a moment. The wire hanging off either creates a potential if the circuit is completed, but cant do any work itself. What you’re basically doing is creating “pipe", but no “water" (current) will flow because you haven't built your infrastructure up completely. So there is a potential for electrons to flow, but you need a completed circuit.

    I’m not trying to be short with you, so no need to apologize, hopefully someone will respond with a better way to explain things then I can come up.
     
  13. Dec 28, 2013 #12

    Who said that you are trying to be short???!!! I never thought of that I actually appreciate your replies,, thanks very much
     
  14. Dec 28, 2013 #13

    davenn

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    sorry, wrong answer!!

    correct answer, no circuit completed, therefore no current will flow .... simple as that
    doesnt matter which terminal of the battery or power supply the single wire is ONLY connected to.
    If there uis no circuit between the positive and negative terminals, then no current flow

    Dave
     
    Last edited: Dec 28, 2013
  15. Dec 28, 2013 #14

    Yes. Some electrons move to the anode, stop there, and neutralize the anode.
     
  16. Dec 28, 2013 #15
    !!!! I'm confused I got 2 different answers to the same post
     
  17. Dec 28, 2013 #16
    I Need to talk someone specialized in electric physics or engineering
     
  18. Dec 28, 2013 #17
    Here is a AC generator and an open circuit:

    O------------G--------------O

    O is a metal ball. G is the generator.

    A current will flow in that open circuit.

    In an open circuit there will be no continuous DC current.


    AC=Alternating current
    DC=Direct current
     
    Last edited: Dec 28, 2013
  19. Dec 28, 2013 #18
    I don't get your point, let's talk about a normal battery and a circuit will there be an instantaneous DC if it is connected to Positive terminal only
     
  20. Dec 28, 2013 #19

    davenn

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    No



    Dave
     
  21. Dec 28, 2013 #20
    Yes. A momentarily DC current.
     
  22. Dec 28, 2013 #21
    http://en.wikipedia.org/wiki/Battery_(electricity)

    here take a read on this article , especially the principle of operation part with the explanation using voltaic cells.
    a battery's terminals if they are not connected in a circuit are not physically connected otherwise , like you would imagine , because if the battery left alone would ahve it's electrons or say neagtive charges flow to the positive then the battery would cancel itself out and the next time you would use it it would have zero current and zero volts inside of it.Because that is what happens whne you leave the battery in a closed circuit after a while.So from this alone you can logically conclude that if the battery terminals are not connected to anything then the electrons dont flow anywhere.
    They start to flow through the battery only when they are driven by the potential difference but to get that you need to physically connect the both terminals in a closed circuit.
     
  23. Dec 28, 2013 #22

    sophiecentaur

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    Batteries are complicated and they add a whole extra level of understanding to this problem. Why not approach this from a more straightforward direction? A power supply (could be a battery, or a wall wart or a bicycle dynamo etc. etc.) will have two terminals. They have a potential difference across them. When not connected to anything, there is a state of equilibrium and no current is flowing. If you connect anything - even just a short length of wire, connected to just one terminal, some charge will flow and the potential will build up on the added item until no more charge flows. The relationship between PD and Charge is called Capacitance. Big objects have a large capacitance and small objects tend to have a small capacitance. If you want a large capacitance (lots of charge for a small PD) you can put two plates / sheets of metal close together, with an insulator (dielectric) between them - a 'Capacitor'. Connect a Capacitor between the two terminals and a lot of charge will flow until it's 'charged up'. If there is no resistive path between the terminals, the charge flow will eventually stop when the capacitor is fully charged and the volts across it are the same as the supply voltage.

    If you really feel you have to talk in terms of electrons then most of the above will apply but, stop and think why electrical engineers very seldom deal in electrons. Do you think it's because they don't understand? Or just possibly, talking Charge, Current Volts etc. is a better way through the problem. If you got the 'electrons' model from School then, along with all the other students, you were probably not done any favours; possibly, the person who had to deliver that model to you (National Curriculum Reequirements and all that) wasn't keen on it or didn't actually understand it.
     
  24. Dec 28, 2013 #23
    Well of course any piece of wire functions as a capacitor and/or inductor, although a random wire hanging off of the positive terminal of <whatever>, and not passing near the negative terminal would be a really, really tiny capacitance. So yes, it would charge like a really, really tiny capacitor does. If it happens to lie close to the negative terminal, the capacitance will be a little more.
    We're talking really, really tiny here - tightly twisted pairs of wire have capacitance in the pF/foot range. Your random wire might be .001 femtofarads or something like that.
     
  25. Dec 28, 2013 #24

    So there would be a potential difference and an instantaneous flowing current when connected to one of the two poles
     
  26. Dec 28, 2013 #25

    TumblingDice

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    It was a question, not an answer. I wanted the OP to explain more behind the thought process.

    For example, where does the cathode begin and end?

    The answer I would offer, rather than simply "the circuit is incomplete", is: "The wire is now the cathode."

    I think that's a better way to describe the given scenario. I didn't think the OP expected the battery the would 'suck out' all of the electrons in the wire...
     
    Last edited: Dec 28, 2013
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