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    Hi all!

    Why is the potential difference the same across each component in a parallel circuit? Whereas in a series circuit the p.d. is shared across the components depending upon the resistance?

    Please help, I am really confused :confused:
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    Same question here
    http://www.thestudentroom.co.uk/show....php?t=2302355
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    Is it possible to answer more scientifically? Thanks
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    In the series case it's because the same current has to flow through each component... When you work out the pd across every component with ohms law, the potential across each component always comes out in proportion to it's contribution to the total resistance.


    In the parallel case all the positive ends of the components are all connected together by conductors and all the negative ends are all connected together by conductors. Every point on a conductor has the same potential so the potential across the parallel components has to be the same.
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    (Original post by Joinedup)
    In the series case it's because the same current has to flow through each component... When you work out the pd across every component with ohms law, the potential across each component always comes out in proportion to it's contribution to the total resistance.


    In the parallel case all the positive ends of the components are all connected together by conductors and all the negative ends are all connected together by conductors. Every point on a conductor has the same potential so the potential across the parallel components has to be the same.

    I honestly do not understand what my book is talking about:
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    ok so back to basics:

    current is a flow of electrons
    Charge is basically a big bunch of electrons (Charge=current x time)
    Charge is measured in coulombs (1 coulomb= 1/1.6x10^-19 electrons)

    Potential difference is the amount of work that a coulomb has to do to overcome the total resistance of the circuit (load resistance).

    a unit of charge has to do work to overcome the resistance encountered when travelling through a component e.g. bulb

    if 3 bulbs are in series, the unit of charge must travel through all 3 bulbs

    if the 3 bulbs are in parallel, the unit of charge only has to go through one. however, regardless of which of the 3 paths it decides to choose the total work it has to do to get from one end of the circuit to the other remains the same, hence that's why voltage is the same all over a parallel circuit
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    (Original post by park1996)
    I honestly do not understand what my book is talking about:
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    i don't like that diagram... I think what it's trying to tell you is that if you set up a circuit with 2 cells in series, and measure the current passing through the cells you'll see the current going through each of the cells must be identical. Which is true.

    What is not true, but what that diagram looks like, is that you can add a cell and the current stays the same.

    As you've probably noticed cells are marked with a voltage but not a current. They're fixed voltage because the reaction producing the pd can only give each electron a fixed amount of energy - the current produced by the cell can however vary depending on the rate the chemical reaction is taking place.
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    (Original post by park1996)
    I honestly do not understand what my book is talking about:
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    Reading the previous paragraph in your book gives the clue as to what the book is trying to say, which I agree is confusing if you are learning this stuff:

    CELL VOLTAGES ADD UP:

    Easy to prove, just stack batteries +ve to -ve terminals and get the sum of the voltages.

    CELL CURRENTS DO NOT:

    The book is trying to say that the TOTAL current AVAILABLE from a single cell CANNOT be increased by simply connecting them in series. To INCREASE the TOTAL AVAILABLE current you need to connect the batteries in parallel.

    This cannot readily be proved on a simulator or even by building the circuit, both of which WILL give you the right answer for the circuit you constructed (i.e. the load has not changed but since I=V/R then stacking the batteries will simply double the voltage and hence double the current), but definitely the WRONG answer for the question you are asking if that makes sense?

    To answer that you would need to find the limiting current of each battery and then connect a load resistance to achieve that measuring the current as you did so. Do that for one battery and then for two series batteries and you will find the current indeed does not increase.

    NB do not try this at home as you will be running a serious fire risk or worse the batteries may explode.
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    (Original post by uberteknik)
    Reading the previous paragraph in your book gives the clue as to what the book is trying to say, which I agree is confusing if you are learning this stuff:

    CELL VOLTAGES ADD UP:

    Easy to prove, just stack batteries +ve to -ve terminals and get the sum of the voltages.

    CELL CURRENTS DO NOT:

    The book is trying to say that the TOTAL current AVAILABLE from a single cell CANNOT be increased by simply connecting them in series. To INCREASE the TOTAL AVAILABLE current you need to connect the batteries in parallel.

    This cannot readily be proved on a simulator or even by building the circuit, both of which WILL give you the right answer for the circuit you constructed (i.e. the load has not changed but since I=V/R then stacking the batteries will simply double the voltage and hence double the current), but definitely the WRONG answer for the question you are asking if that makes sense?

    To answer that you would need to find the limiting current of each battery and then connect a load resistance to achieve that measuring the current as you did so. Do that for one battery and then for two series batteries and you will find the current indeed does not increase.

    NB do not try this at home as you will be running a serious fire risk or worse the batteries may explode.
    I'm sorry, but I don't understand what this means!
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    (Original post by Joinedup)
    i don't like that diagram... I think what it's trying to tell you is that if you set up a circuit with 2 cells in series, and measure the current passing through the cells you'll see the current going through each of the cells must be identical. Which is true.

    What is not true, but what that diagram looks like, is that you can add a cell and the current stays the same.

    As you've probably noticed cells are marked with a voltage but not a current. They're fixed voltage because the reaction producing the pd can only give each electron a fixed amount of energy - the current produced by the cell can however vary depending on the rate the chemical reaction is taking place.
    Thank you!
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    (Original post by park1996)
    I'm sorry, but I don't understand what this means!
    OK.

    The maximum current available from any battery will be limited by how fast the internal chemical reactions can generate that current.

    You can't pull more current than the rate of the internal chemical reaction will allow.

    That means in series, the current will be limited by the slowest reaction in any given battery because the same current must flow through all the batteries in the series connection.

    However, in parallel, current can be pulled from any battery independently and so the available current is the sum available from all the batteries.
 
 
 
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