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Flow of electrons

  1. Oct 9, 2012 #1
    in a battery, when all the electrons have transferred to the positive terminal ( i mean both terminals have same no. of electrons) , then do any current flow? if no , then how much time does it take for all electrons to be transferred fron negative to positive terminal? (i know it is a silly question but i need an easy logical answer)
     
  2. jcsd
  3. Oct 9, 2012 #2
    Both terminals always have the same number of electrons.

    A battery participates in a closed circuit.

    In the ouside part of the electrical circuit we can say electrons move from the negative terminal towards the positive.

    Within the battery they move the other way, completing the circuit and so maintaining the number around the circuit.

    The electron 'movement' is powered by the chemical reaction within the battery.
    This reaction cannot take place unless the circuit is completed externally so current only flows in a complete circuit.
    When the chemicals are all used up the reaction ceases and so does the current.
    The time for this to happen depends upon the current draw by the external circuit and the available quantity of chemicals internally (ie battery size or capacity).

    Does this help?
     
    Last edited: Oct 9, 2012
  4. Oct 9, 2012 #3
    first of all, the positive and negative terminals obviously DO have different numbers of charged particles...be they ions or electrons...otherwise there would be no potential difference between them....just as there are more negative charges on one plate of a capacitor than the other ....

    see here for basic battery operation:
    http://en.wikipedia.org/wiki/Battery_(electricity)#Principle_of_operation


    You can get some standard figures to compare batteries regarding how long they will deliver current from the ampere hour rating and Peukert's Law:

    http://en.wikipedia.org/wiki/Automotive_battery#Terms_and_ratings
    http://en.wikipedia.org/wiki/Peukert's_Law


    Although I don't think automotive batteries typically have an ampere hour rating provided
    [ they seem to use cold cranking amps [CCA]as a standard measure] all deep cycle batteries that I have seen do. These ratings are usually based on a 20 amp discharge rate in the US....so an 8D deep cycle lead acid battery, for example, might have a rating of about 220 amp hours....at 20 amps, it will provide current for 220/20 or about 11 hours....after which the voltage is down to 10.5 volts....many loads will not work at or beyond that but additional current will flow at a reduced rate.

    Peukerts law is the more accurate way to calculate how long a current will continue to flow.
     
  5. Oct 9, 2012 #4
    If this is true then the salt bridge in your Wiki article should not necessary. Simply connecting the terminals by a wire should enable all these excess electrons to flow between the half cells without the bridge.

    Of course this cannot and does not happen so perhaps you would like to explain further?
     
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