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Potential in a capacitor

  1. Nov 24, 2004 #1
    how does the potential increases on adding positive charges and decreases on adding negative charges.
    why does the the existence of capacitor does not have any effect in a circuit with resistors and battery
  2. jcsd
  3. Nov 24, 2004 #2
    If you add charges, negative or positive, the potential difference between the plates of a capacitor increases. The reason is that always an equal charge of opposite sign in induced on a plate whenever you put a charge on another of the plates. So, since the ratio of charge and potential diff. is the constant ( and equal to capacitance ), the potential diff also increases.

    Existence of capacitors has an effect on the circuit. The current increses slowly and decays slowly etc.

  4. Nov 24, 2004 #3

    I have got into trouble before for this reply -- it is however true.
    Potential is a very odd unit -- it is the amount of work done on a unit charge ( e.g. an electron ) in moving it thru an electric field from one place to another. the unit is therefore work ( joules ) per unit charge. specifically it is the work done in moving the unit charge from an infinite distance to the one under consideration. ( this is a precise definition )
    It follows that if you move more than one charge then the potential is proportional to the number of charges . ( it just takes more work )
    We have more misunderstanding of this unit than almost any other , because it envokes all sorts of images -- most of which are not true.
    for instance volts are NOT a force . potential is not like temperature
    there is NO absolute potemtial .
    Because there are many definitions of the volt ( to do with how it maybe measured ) it is a really confusing situation.
    However there is only ONE definition if you look at the units implied ( see dimensional analysis ) the basic metric is MKS -- meter kilogram second -- to which we have to ADD charge ( because it does not belong to the others ).
    This is why the measure of potential includes our normal metric but adds charge.
    What I am talking about here is the formal definition , NOT peoples idea of what this means . So take care and read up on any formal physics book for this definition.
    My personal advice is NEVER look up a 'forum' for definitions , they are full of peoples opinions which for the most part are innaccurate , and totally biassed -- any body who has the gall to call themselves a ' super mentor '
    should be shot !!!!!!!!!
    I do not know if this helps -- but it was a 'try'
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