Current without a ‘closed circuit’?

It’s common knowledge that you need a ‘closed circuit’- an unbroken, continuous, conducting path- for an electric current to flow. If you are using a battery, this usually means an unbroken path from the positive terminal of the battery, through an LED (or whatever device you are running), all the way to the negative terminal of the battery.

But the closed loop between the terminals of the battery is strictly not necessary. What is important is that an electric current needs to flow through the LED, and for this all that is required is that the LED is connected between two points at different electrostatic potentials. The terminals of a battery contain static charges, and one could theoretically draw a small current for a small duration if we connected an LED between one terminal of the battery and a neutral object. The neutral object will act as a source or sink of electrons, depending on whether we are connecting it to the positive or negative terminal respectively. But for the chemical reactions in the battery to continue happening to provide a continuous current, the other terminal also needs to be operating (this is something that needs discussion, but I’ll do it in another post).

To test this out, I connected the positive lead of the LED to the positive terminal of a 9V battery, and held the negative lead with my fingers (myself being the neutral body). Obviously the LED didn’t light up. But then I connected the negative terminal of the battery to the earthing in an AC mains socket, so that it can act as a sink for electrons from the negative terminal of the battery. And the LED lit up! Not brightly, but that’s understandable, since my body has a large resistance.

Here’s a photograph of the LED glowing when I touch its negative terminal. The second picture shows the LED when it’s off, so that you can see the difference.

5 thoughts on “Current without a ‘closed circuit’?

  1. I don’t think the experiment you performed verifies the statement you made about closed loops not being required for an LED to work on a battery.
    When you connected the negative terminal of the battery to earth and the cathode of the LED to yourself, all you did was you provided a closed path for the current to flow from the battery through the LED -> you -> earth -> ground terminal -> and back to the battery. Electrostatics was not involved in the operation of the lamp. What you did is equivalent to simply connecting a large resistance in series with an LED and a battery. That one of the points on the path was ground did not influence the battery or LED in any way.
    Also, while it is true that charge can flow between points at different electrostatic potentials, generally such collected charges tend to be extremely small and can never light up an LED for a noticeable period of time. Maybe, ESD could damages a sensitive enough semiconductor, but cannot power one. And even if you could find a big lump of electrostatic charge somewhere, I would bet it wouldn’t be on a battery. They are more easily accumulated on insulators as they tend to collect and hold charge in one place instead of easily giving it back.
    Also, for the operation of circuits, KIL dictates that unbroken paths are a must.

    1. When you connected the negative terminal of the battery to earth and the cathode of the LED to yourself, all you did was you provided a closed path for the current to flow from the battery through the LED -> you -> earth -> ground terminal -> and back to the battery.

      I don’t disagree with you. That’s the ‘circuits way’ of looking at it. But if you look closely at the electron flow and the reactions happening in the battery, you’ll see that you just need an electron sink connected to the negative terminal of the battery and an electron source connected to the positive terminal of the battery for it to work and the electron source and sink can be theoretically two very large neutral objects, completely independent of each other.

      You are probably right that in this experiment there is a physical connection between me-earth-battery negative terminal through a large resistance. But the question is, is the current flowing because of the unbroken path, or because electrons are pulled out from one side and pushed in from the other?

      I’m trying out some other experiments where this physical connection doesn’t exist. Then the ‘circuits’ model will be that of a capacitor, and the current should flow till the capacitor gets charged (which would be a long time if the neutral objects have a very large capacitance). Will write more about them later.

      Electrostatics was not involved in the operation of the lamp.

      This is not true. It’s a common misconception that current electricity has nothing to do with electrostatics. But for an electric current to flow between two points there needs to be a difference in their electrostatic potential, and this is caused only by imbalances of charge.

      While teaching electrochemistry, I was studying how exactly electrochemical cells function, and it seems that there are static charges that build up on the electrodes which is what makes the current start flowing in the first place. Of course, these static charges are at too small a potential compared to the static charge that builds up on insulators in winter which is of the order of thousands of volts of potential.

      The static charge itself on the battery terminals is not insignificant (in fact a typical battery electrode seems to have around tens to hundreds of micro Coulombs according to calculations which I did based on the models of electrode-electrolyte interface), it’s just that the potential is quite small.

      Check this out, misconceptions coming from the unnecessary divide between electrostatics and current electricity. http://amasci.com/emotor/stmiscon.html

      1. It is useful to keep in mind that electroctatics refers to the condition which is attained when charges have distributed themselves (on conductors) in such a manner that equilibrium is established – no force on any charge. During any change in the distribution, currents flow, current being charge in motion. The (re)distribution process lasts for a very short time. – the relaxation time of the conductor which is of the order of nanoseconds.
        As part of Kishor’s experiment, one could set up a magnetic compass needle near the connecting wire which is simply transferring charge from one conductor to another. It should give a kick when current passes even for a short time.
        More comments later.
        A S Mahajan

      2. “But if you look closely at the electron flow and the reactions happening in the battery, you’ll see that you just need an electron sink connected to the negative terminal of the battery and an electron source connected to the positive terminal of the battery for it to work and the electron source and sink can be theoretically two very large neutral objects, completely independent of each other.”
        It depends on what you call “working” of the battery. If you connect the 2 terminals to 2 large completely independent neutral bodies, the battery will simply see a large capacitor as load and charge it up until the potential of the cap reaches the battery voltage. After that current flow will stop. So, no matter how large the bodies are, an LED connected in series will glow only while the transient current is flowing. After that it will stop.
        “But the question is, is the current flowing because of the unbroken path, or because electrons are pulled out from one side and pushed in from the other?”
        I didn’t get this question. The current is flowing because charges are being pushed in and pulled out and also because there is an unbroken dc path between the terminals through which the current can flow.
        “This is not true. It’s a common misconception that current electricity has nothing to do with electrostatics. But for an electric current to flow between two points there needs to be a difference in their electrostatic potential, and this is caused —only by imbalances of charge.—- ”
        I said that the LED glowing is not because of any static charge accumulation. When the battery is disconnected it might accumulate charge on its terminals. But, once the circuit is closed, there is no longer any static charge getting collected anywhere. As charge moves into a terminal, electron transfer happens simultaneously at the electrode-electrolyte interface to maintain the surface potential. It is a “dynamic” phenomenon.
        Thus, the charge on the terminals of a battery connected in a closed circuit is not really static. I am not very certain of this thing. But my main point was that the LED glowing in this case was the result of a closed path and thus the experiment cannot be used to test whether a current can flow in the absence of one.

      3. You’re right. I get it clear in my mind now.

        In the absence of a closed path, if two neutral objects were acting as electron source and sink, current flows only till the potential difference between them reaches the battery voltage. It’s a transient current. Even if the objects are large, it will flow for a little longer, but it’ll be transient.

        For the current to be continuous, you need to take away electrons from and give electrons to the initially neutral, now oppositely charged objects, and this can happen only if there is some kind of a conducting path between the two. So in circuit components’ terms, it’s either a resistor if the two objects are connected and a continuous current can flow, or a capacitor if the two objects are not connected and only a transient current flows.

        In my mind I was not making the distinction between transient and steady state currents, and obviously in this case it is a steady state current.

        Regarding battery terminals, there are static charges on the electrodes when it’s not connected. The best explanation I have found for the process at the electrode-electrolyte interface is here- http://www.chem1.com/acad/webtext/elchem/ec1.html#ENEUT

        And the charge distribution at the electrode-electrolyte interface is modelled as something similar to a capacitor.

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