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The battery and its potential difference

  1. Nov 12, 2013 #1
    Hello everybody :smile:
    can anybody explain to me why there is potential difference in the battery (and when we say the potential difference of the battery is Va-Vb =12 v can both electric potentials be positive for example Va=20v and Vb =8v ) . From the last , can somebody illustrate to me in a deep way how the battery works and how it produce emf..?
    and thanks a lot :smile:.
  2. jcsd
  3. Nov 12, 2013 #2


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    Batteries have a positive terminal and a negative terminal.Normally,a simple battery is a cell.(As far as I know)The cells works by electrolysis.Two metals with a different reactivity is used.The two metal is then dipped into the electrolyte and connected with a wire above the electrolyte.The electrons flow from the more reactive metal to the less reactive metal,as more reactive metals tends to lose electrons more easily(not through the electrolyte,but through the wire above it,which connects two metals to complete the circuit.).So the more reactive metal is the negative terminal and the less reactive metal,the positive terminal.The greater the difference in the reactivity,the greater the emf produced.
    (If you know chemistry,I will explain it more)
  4. Nov 12, 2013 #3


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    I don't think the electric potentials can both be positive or negative unless you electrically charge the whole battery. (which I've never heard of) Still, this potential would be with reference to ground, not between the terminals, so it doesn't really matter.
  5. Nov 12, 2013 #4
    the problem is that I am weak in chemistry . if you can illustrate in a physical way?
  6. Nov 12, 2013 #5


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    Electrolysis is the process of decomposition of a molten or ionic aqueous salt solution using electricity.When the two metal is connected by a wire,the more reactive metal tends to lose electrons,so electron travels through the wire to the less reactive metal.(it is now dipped into the electrolyte(molten or aqueous salt solution,acid or alkali))the electron transfer makes the more reactive metal positively charged,making it the anode(which attracts negative ions or anions)Anions in the electrolyte gets discharged there,giving electrons to the metal.On the other hand,the less reactive metal is now negatively charged(as electron has traveled to it).It becomes cathode(attracts cations or positive ions)Cations gets discharged there taking electrons away from the less reactive metal.So,the electrons now travel round the circuit,until the electrolyte depletes.
  7. Nov 12, 2013 #6
    thanks for your effort. But I just want to understand it physically. I know that V1=Qk/r1 V2=Qk/r2 V1-V2 produce emf , I want it to be illustrated in a physical way with out any chemical details as much as possible .
  8. Nov 12, 2013 #7


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    I'm not sure it's possible to understand how a battery works without getting into some basic chemistry.
  9. Nov 12, 2013 #8


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    I am with Drakkith on this, a battery is a chemical device. To understand how one works requires chemistry. No satisfactory explanation can be given without mention of chemistry.
  10. Nov 13, 2013 #9
    ok thanks ..
  11. Nov 13, 2013 #10


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    I could take a 12V battery and put it in series with a 1000 V DC source and the battery terminals could be..

    -ve terminal 1000V
    +ve terminal 1012V

    If you have a toy that uses three 1.5V cells in the battery the voltages would typically be

    Cell 1 -ve = 0V (I define it so)
    Cell 1 +ve = 1.5V
    Cell 2 -ve = 1.5V
    Cell 2 +ve = 3V
    Cell 3 -ve = 3V
    Cell 3 +ve = 4.5V

    Overall voltage of the battery is Cell 3 +ve minus Cell 1 -ve which is 4.5 - 0 = 4.5V

    I run the toy across a nylon carpet so it picks up some static electricity, then relative to earth the voltages might become

    Cell 1 -ve =10,000V
    Cell 3 +ve = 10,004.5V
  12. Nov 13, 2013 #11


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