Why is there no current flow when I connect two opposite terminals of two separate batteries?

13,606

Solution 1

There exists a similar question here.

This description of a voltaic battery solves the conundrum which the question raises:

daniell cell

If one connects the + and - of the same battery with no resistance, one shorts and discharges it anomalously. There should always be a resistance ( the lamp in the drawing) on the same battery.It is clear in the diagram that a chemical path exists, a current of ions that closes the circuit and current flows.

A chemical circuit has to be closed for current to flow. Two different batteries have two different chemical flows . Electrons that might leave the anode to go to the cathode of the other battery cannot close the chemical circuit of the parent cell because the ions have no reason to move as no charge has gone to the copper cathode of the original cell. At the same time the second cell is at the same fix , as no chemical circuit is closed there too, no charge has left the zinc anode, no motion of ions possible.

Solution 2

Under the scenario you presented, all you've done is made a bigger battery. Which is just sitting there, so there is no current flow. If you open up a standard 9 volt rectangular battery you will find six 1.5 volt cells connected in series, i.e. exactly as you described.

Solution 3

It's common for almost all analogies to break down at some point when the phenomenon is understood at a deep enough level. In the very old days indeed electricity was thought of as a fluid and a concept of 'pressure' and 'flow' was used. However electrons are not marbles. Most commonly they move because they are in an electric field, not because anything is bumping into them. Now to answer your 2 questions it is simpler to understand a battery as a thing that exerts a potential difference (voltage) between the 2 terminals. The gradient (derivative) of the voltage is proportional to electric field:

  1. If you connect a conductor to a battery terminal the conductor becomes the same potential as the battery terminal, and the potential difference becomes 0, so there is no electric field.

  2. If you connect the - terminal of a battery to the + terminal of another battery, the contacts will be at the same potential (because they are conductors). Then the potential difference between the 2 contacts is 0 and again there is no electric field.

Share:
13,606

Related videos on Youtube

Muhammad Umer
Author by

Muhammad Umer

Updated on November 26, 2020

Comments

  • Muhammad Umer
    Muhammad Umer almost 3 years

    I don't understand this..maybe there is something wrong with my understanding of battery or electricity.

    I am learning about electricity more deeply this time. So please bear with me.

    So lets begin with what I know:

    • follow of current occurs when there is voltage drop.
    • voltage drop happens when there is imbalance in charge.
    • a battery is basically two separated chemicals. One side with electrons to spare and other side that needs electron to balance itself. which is imbalance in charge.
    • When both sides are connected + side snatches electrons from - side. (And if there is a medium, conductor, then first electrons are taken from conductor that in turn snatches from - side, which not being able to keep electrons lose them and give up those electrons, we label it as excessive.)

    The analogy i was taught with used marbles in pipe... When one side has excessive marbles And this pipe is connected to other side that has no marbles the marbles will instantaneously start falling out so even though marbles from container with excessive marbles haven't traveled there yet, they still start falling because filled side marbles are pushing marbles in pipe and which in turn push the last marbles in pipe out.

    1st, Aren't electrons pulled by atoms that can use more electrons, and not move because one side is overfilled with electrons so they can't wait to push some out.

    Questions:

    1. if I connect a conductor to positive side of a battery, shouldn't it make all electrons/marbles fall into empty container as empty container will pull marbles as atoms need electrons?
    2. if I connect two batteries' only opposite sides to each other shouldn't they drain (balance the each other out, cancelling all - & + charges)?
  • Muhammad Umer
    Muhammad Umer almost 10 years
    about 2, why is potential energy zero when side has excessive and other side lacks electrons. Why there is no potential here.
  • justin
    justin over 7 years
    :Could you tell why we use electrolyte?I'm really confused where the oxidation,reduction etc takes place.To be honest I know that the flow of electrons(from zinc metal) are produced by the attraction of electrons towards the protons(copper metal) as seen in this video.I can't get why do we need an extra potential to make the current flow and why do we use an electrolyte that has no role in flow of electrons.Could you help me.
  • anna v
    anna v over 7 years
    @justin electrolyte provides charge mobility, in the link provided: "As a zinc atom provides the electrons, it becomes a positive ion and goes into aqueous solution, decreasing the mass of the zinc electrode. On the copper side, the two electrons received allow it to convert a copper ion from solution into an uncharged copper atom which deposits on the copper electrode, increasing its mass."
  • justin
    justin over 7 years
    :Sorry but I couldn't get how electrolyte provides charge mobility.Do you mean to say that due to the potential difference in the electrolyte,electrons get an energy to move from zinc rod to copper rode through the wire?
  • anna v
    anna v over 7 years
    look at the diagrams, the electrolytes have electrons and ions that provide the current in the electrolyte and exchange copper and zinc
  • justin
    justin over 7 years
    :Yeah I could see that to obey the principle of electroneutrality the $Zn^{2+}$ ions are attracted by the $SO_4{2-}$ ions.Could you tell why does zinc losses two of it's electrons?
  • anna v
    anna v over 7 years
    @justin It is the effective potentials from the various bonds. It is not my field, but when energy exchanges happen it means that there are lower energy states for the ions and electrons to occupy which appear when the circuit is closed.
  • justin
    justin over 7 years
    :Could you tell whether we could get current by connecting a wire through an electrolyte so that electrons from the electrolyte goes to the protons in the electrolyte as said in the video.
  • anna v
    anna v over 7 years
    Yes, it is correct, it is a temporary current. I do not like the continuation, which glosses over what the diagram in my answer shows. A complete mix they are showing will discharge the battery.
  • justin
    justin over 7 years
    :Could you tell how does an electrolyte provides an continuous current.That's where I'm stuck.
  • anna v
    anna v over 7 years
  • justin
    justin over 7 years
    :I really couldn't get this sentence:"In order for the voltaic cell to continue to produce an external electric current, there must be a movement of the sulfate ions in solution from the right to the left to balance the electron flow in the external circuit. ".Could you help me.
  • anna v
    anna v over 7 years
    The sulfate ions carry the negative charge in the solution, the electrons in the metal.Notice the -2over the SO2 in the drawing in the answer. charge is conserved all around
  • justin
    justin over 7 years
    :Okay.Does this process goes on for ever or does it stop anytime?
  • anna v
    anna v over 7 years
    It stops when the solutions become saturated with zink on one side and all the copper depleted, just SO2 on the other, then the battery is discharged and has to be charged again.
  • justin
    justin over 7 years
    :Could you tell how does copper gets depleted.I think copper ($Cu(s)$) actually gets deposited on copper rode after it ($Cu^{2+}$) accepts electrons from zinc.
  • anna v
    anna v over 7 years
    @justin I mean that it is depleted from the solution , it becomes a part of the solid,
  • justin
    justin over 7 years
    :Oh sorry about that.Could you tell whether an electron can flow from zinc to copper through a wire without an electrolyte.I would like to know whether the electrolyte is responsible for turning $Zn(s)$ into $Zn^{2+}$ ions.
  • anna v
    anna v over 7 years
    @justin if you read the explanation you will see that the electrolyte is necessar "placing zinc and copper metal in solutions of their salts can cause electrons to flow through an external wire which leads from the zinc to the copper. " Just copper and zinc are neutral and there is no force to make electrons move. hyperphysics.phy-astr.gsu.edu/hbase/chemical/… . A chemical reaction takes place.
  • justin
    justin over 7 years
    :Yeah that's truely right.
  • justin
    justin over 7 years
    :Can we use water as an electrolyte for the zinc and copper reaction?Also as you said here could you tell whether it's $SO_4$ or $ZnSO_4$ on the other side of copper?Using only zinc rod,$ZnSO_4$ and $CuSO_4$ can we get the same reaction that we get when use zinc rod,$ZnSO_4$ and $CuSO_4$ and copper rode?I thinks there's no need of using a copper rode since copper only gets deposited.
  • anna v
    anna v over 7 years
    @justin if the copper is not deposited the SO4 will not carry a charge(-2), read the diagram, it shows how ball is played with the charges and the copper and zink . There can be other electrolytes, but not randomly guessed. The chemistry has to work. .
  • justin
    justin over 7 years
    :Do you mean to say that if the copper gets deposited in the $CuSO_4$ solution rather than getting deposited at the copper rode the chemical reaction wouldn't take place.I would like to know whether the electrons from zinc could be transferred to the $CuSO_4$ solution instead of depositing them on the copper rode so that the $Cu_{2+}$(aq) ions could accept these electrons and turn $Cu$(s) in the $CuSO_4$ solution itself instead of getting deposited on the copper rode?
  • anna v
    anna v over 7 years
    @justin I cannot teach chemistry. The way the chemical reaction works has been utilized in the set up of the battery. There is no if about the way the energetics of chemical reactions go.
  • justin
    justin over 7 years
    :Oh sorry about that.Could you tell whether $Cu_{2+}(aq)$ has a greater affinity for $Cu(s)$ rod than for $CuSO_4$ solution?
  • anna v
    anna v over 7 years
    @justin I am sorry, no, although I can guess since copper containers were popular before stainless steel that not much copper is dissolved in water.
  • justin
    justin over 7 years
    :No problem.Since copper doesn't get too much dissolved in water is it better to deposit copper in water than depositing it on a copper rod?
  • anna v
    anna v over 7 years
    @justin I do not understand you question. The whole point of an electrolyte that can deposit on coppe and dissolve from zink is the carrying of charge as seen in the diagram. This cannot happen with water. Bye Bye
  • justin
    justin over 7 years
    :Oh sorry I meant to say about $CuSO_4(aq)$ solution rather than water.Could you now help me.
  • anna v
    anna v over 7 years
    @justin I still do not understand the question . The diagram says it all. Better find a chemistry question and answer site. I do not know enough chemistry to answer further
  • justin
    justin over 7 years
    :Oh that's no problem.I'll ask it here.A great site indeed for any science questions.
  • ChemEng
    ChemEng almost 4 years
    The Cu2+ ions stay on the right side of the cell they are not permeable through the membrane only sulfate is. Some people use 2 separate jars with a salt bridge (KNO3) instead of a semipermeable membrane. The electrolyte is typically non-conductive so the electrons cannot flow through it, they have to flow through the external circuit.
  • ChemEng
    ChemEng almost 4 years
    If Cu2+ ions were at the zinc anode yes they may be reduced and the energy would then not be used as electricity instead it would be released as heat.It is important to use electrolytes that do not undergo oxidation or reduction at the anode or cathode or a full redox rxn will occur at the terminal instead of a half one