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Are the terminals of a well-charged battery neutral?

  1. Jan 31, 2009 #1
    Hi,It may looks illogical but concepts of electrostatics and current electricity force me to think so..'Are the terminals of a well-charged battery neutral?'my dc fan doesn't work when one of its wire is connected to the positive terminal of one battery and the other wire of the same fan to the negative of another battery.while its ok using only one battery.Is it possible for two bodies'of about same finite capacitance' being oppositely charged to have no potential difference?Please explain.Thanks a ton.
     
  2. jcsd
  3. Jan 31, 2009 #2

    turbo

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    You have to have a complete circuit for electricity to flow. Can you do this with two separate batteries?
     
  4. Jan 31, 2009 #3
    Thanks Turbo-1 for your attention to my question.But as far as i know whenever their is potential difference between two bodies,current flow from higher potential to lower potential till both the bodies attain same potential.in texts they show two they bodies of oppositely charged when connected by a single wire electrons flow flow from negatively charged body to positively charged body.
     
  5. Jan 31, 2009 #4

    turbo

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    This can only happen when you have a complete circuit through which the current can flow. Draw it out.
     
  6. Jan 31, 2009 #5
    It sounds that your answer for the question 'why current produce?' to be due to complete connection of wires rathar than due to difference of potential.
     
  7. Jan 31, 2009 #6

    turbo

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    You need both. Draw out a picture of your batteries with their poles, the wires and the load (fan in this instance).
     
  8. Jan 31, 2009 #7
    Ok upon your advice i draw a diagram but still i am confused.See, does it just nead for the current to have its wires end to be connected to the source or is it also necessary for the terminals of the source to be connected through any conducting material besides the wire.If the latter'as per your view' why do a capacitor is able to draw current,when its two charged plates are not connected by a conductor.I think you need to re-look at the defination of close circuit.
     
    Last edited: Jan 31, 2009
  9. Jan 31, 2009 #8
    I mean a close circuit should have been defined as the one in which the load must be connected i.e.the two wires join connecting the load from both sides, and the other ends of the wires must be connected to the terminals which have potential difference,irrespective wether the terminals are themselves are joint or separated from each other but they must have p.d.Please correct me if i am wrong.in ac also we can use phase wire of poles and can make the tab etc as neutal to run load
     
    Last edited: Jan 31, 2009
  10. Jan 31, 2009 #9

    turbo

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    Wrong. The two terminals cannot just have different potentials, but must be connected to one another to supply a path for current to flow.

    You can prove this to yourself with a 2-cell flashlight. When the batteries are touching one another and you turn on the switch, the bulb lights up. If you take out the battery at the back of the flashlight and put a piece of tape over the small (+) terminal and reinsert it, you won't be able to turn the light on because you have interrupted the circuit. The bulb is still connected to the positive end of one battery and the negative end of the other battery, but no current can flow because you have interrupted the circuit.
     
  11. Jan 31, 2009 #10
    So how is it possible for a capacitor and ac 'as i mentioned' to work,when their source terminals are not connected.And how does it possible for two oppositily charged spears to pass current when joint by a wire,while no cyclic connection is their.I think you need to look deeper.
     
    Last edited: Jan 31, 2009
  12. Jan 31, 2009 #11

    turbo

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    I'm sorry. You'll have to educate yourself, since you seem intent on ignoring every bit of help that I have given you.
     
  13. Jan 31, 2009 #12
    Well explain me how capacitor is able to draw current when its two wires are connected to a load.You must have been known that the plate of a capacitor are made of a conductor,and these plate have no conducting connection between them.The plates of a charged capacitor have equal and opposite charge but they are remain separated with a insulator weather the capacitor is working or not.so please explain me when oppositely charged separated plates can draw current why can't two oppositely charged termns can
     
  14. Jan 31, 2009 #13

    turbo

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    You seem unable to grasp the concept of current-flow through a resistive load in a circuit. There is no point in discussing the behavior of capacitors until you have gotten past that simple concept.
     
  15. Jan 31, 2009 #14
    O' Tor do not feel me bad.I just want to understand things.May their be some sort weakness in my mind due to which i am not getting you.I do not intend to tease any body.What that is going on either you are feeling difficulty understanding me or it may be some problem with me.Hope you are not dissappointed with me.
     
  16. Jan 31, 2009 #15
    O' Tor do not feel me bad.I just want to understand things.May their be some sort weakness in my mind due to which i am not getting you.I do not intend to tease any body.What that is going on either you are feeling difficulty understanding me or it may be some problem with me.Hope you are not dissappointed with me.Do any body know my answer?Please help.Thanks
     
  17. Jan 31, 2009 #16
    Consider two identical spears of iron ,if some how one spear is given neagtive charge and the other is given a positive charge.And thesd two spears are then place 10meter apart with both separatly on an insulated stand.Now the the spears are connected to nothing other than air or say they are in vacuum.Now could you tell me what happen when this system of two spears is joint by a wire.The spears are themselves in no connect other than external wire or external circuit.Thanks.
     
  18. Jan 31, 2009 #17
    If you have two separated bodies of opposite charge, the charges will try to neutralize : if you touch the first of your "iron spears" (say negative one) with an iron wire, the excessive charge on the spear will distribute across both spear andwire, but you will notice nothing of that. If you now touch the positive "spear" with you wire, you'll most probably observe a spark (=short manifestation of charge neutralization, or so to say, "current"): you could call this electrostatic discharge (ESD), if you like.

    If there is no machinery which supplies new charge to the "iron spears", this spark will be the only thing which happens
     
  19. Jan 31, 2009 #18
    It is possible to have current flow when arranged as you've stated, but it requires far greater voltage potentials and the flow is typically brief, lasting only as long as is required for both points to reach the same level of charge, at which point no additional current will flow. 12 volts is just too low to accomplish the task.
     
  20. Feb 1, 2009 #19

    Mapes

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    This is a good question, ovais. Indeed, current will flow between two objects if one is negatively charged, one is positively charged, and they are connected by a wire. And current will flow if you connect the positive terminal of one battery to the negative terminal of another, but only briefly.

    See, a battery operates by containing chemicals that tend to react. When the reaction occurs, ions (i.e., atoms bearing charge) are pushed from one electrode to another within the battery. At the negative electrode, each ion changes to an uncharged atom and an electron or electrons. At the positive electrode, an electron or electrons combines with an uncharged atom to produce an ion. The ions move through a paste called an electrolyte (by definition, a substance that allows ionic charge transfer).

    When the battery is assembled, the same reaction occurs briefly, until electrons build up on the negative electrode and are depleted at the positive electrode. This quickly stops the reaction. The battery is now ready for use.

    When you connect the positive terminal of one battery to the negative terminal of another, the reaction will continue briefly and charge will flow briefly, but you haven't fulfilled the requirements for continuous power because the negative terminal of the first battery still has a surplus of electrons and the positive terminal of the second is still depleted of electrons.

    It's only when you connect a load to a battery or batteries in a circuit loop that you can transfer electrons from the negative electrode to the positive electrode via electronic current flow. This allows the reaction to continue. Does this make sense?
     
  21. Feb 11, 2009 #20
    hello mapes, first of all thank you your answer makes full sense you seem to understand my query.you have answered from inside the battery that's what i want.now i very much understand why charge don't continously flow from one battery to another as you said.But I will be very thankfull to if you explain this more openly and in more informative way,since i at this stage is satisfied with it but still can not explain it to others on my own.REGARDS
     
    Last edited: Feb 11, 2009
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