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newcomer battery question

Discussion in 'Electronic Basics' started by Anders Lindén, Jan 20, 2004.

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  1. Hello!

    I wonder why there is no currency in this "circuit" between
    the two batteries.


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    I have heard the explanation that the batteries wants
    "balance", and therefore
    the electrons from one of the batteries doesnt want to
    travel to the other battery,
    even if there is a shortcoming of electrons there. But, as I
    have understood it,
    there are two chambers in a battery that ideally are
    isolated from each other and
    doesnt "communicate".

    /Anders
     
  2. Greg Neill

    Greg Neill Guest

    There is no circuit. A circuit is so named because it
    implies a closed loop, a complete path around the
    components.
     
  3. True, there is no curcuit. I was writing "curcuit" to denote
    that I was aware of it.
    /Anders
     
  4. Greg Neill

    Greg Neill Guest

    Well, that's the answer to your question. No circuit equals
    no continuing flow. What you've got instead is an exercise
    in static electric charge distribution. Assuming both
    batteries are overall neutral in charge, connecting them
    any which way you please without completing a circuit so
    that their chemical energy can drive a current, you'll have
    no current flow.
     
  5. But isnt a battery consisting of two chambers that are
    isolated from each other?

    /Anders
     
  6. Ross Mac

    Ross Mac Guest

    That's easy....no load no current !!
     
  7. The fluid analogy for a battery is a pump that produces a constant
    pressure difference between inlet and outlet. Your diagram is thus
    equivalent a pump with a tall pipe connected to its outlet and the
    weight of the fluid standing in the pipe is balancing the pump's
    pressure, so the fluid is standing still. No work is being done so no
    energy is being consumed. But there is a pressure difference
    (voltage) between the top and bottom connection.
     
  8. Greg Neill

    Greg Neill Guest

    Well, it's a little more complicated than that.
    Batteries separate charge via chemical means.

    But even so, no charge is created out of nothing in
    the battery; the total number of electrons and
    protons remains the same, hence the battery, taken
    as a whole, is neutral.

    The potential difference between the two poles of the
    battery consists of equal and opposite charges. The
    total potential difference depends upon the chemical
    potential driving the charge separation, typically
    on the order of 1.5V for a unit cell. Once that
    potential difference equals that of the chemical
    potential, no further charge separation can occur.

    If you drop an electron onto the positive terminal,
    it will cancel one electron's worth of the charge,
    and the chemical cell will be able to separate
    another electron and send it to the negative pole
    to balance the charge. The entire battery will
    then have a net negative charge equal to that of
    the single electron that you put on it. This net
    charge would make it a bit harder to add another
    electron in a similar fashion. After a while,
    you'd find it impossible to add more electrons to
    the positive pole without first taking some away
    from the battery, because the battery will have
    a high overall negative charge.

    The solution is to take an electron off the
    negative pole each time you add one to the
    positive one. This keeps the battery overall
    neutral in charge. This is also why you need
    to have a complete circuit. Otherwise you quickly
    accumulate charge which prevents further movement.

    When you connect two batteries as you've shown, the
    effect is similar to connecting a chunk of inert
    metal to one pole of a single battery. There may
    be a brief, miniscule pulse of current while the
    charge spreads over the metal surface, but it will
    amount to a very tiny and short lived shifting of
    charges. The whole metal chunk will have a net
    1.5V charge with respect to the other pole of the
    battery. Once this situation obtains, no further
    current can flow.

    Let's imagine a simple mechanical analogy. Let's
    say our "battery" is a length of pipe filled with
    water. In the center of the pipe is a little
    pump which tries to pump water from the top of
    the pipe to the bottom. It has a fixed pressure
    rating, so it tries to maintain this fixed
    pressure between the ends of the pipe. When there
    are no connection to the "battery", no current
    can flow.

    Now you stack two of these pipes, one on top of the
    other and connect the touching chambers. You still
    have no connections to the remote ends. How much
    water can flow?

    If you connect a tube from the bottom of the stack
    to the top, what happens?
     
  9. Ok, put a resistor between the batteries then.

    /Anders


    net...
     
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