Capacitance

Discussion in 'General Science & Technology' started by Skulking Lurker, Oct 24, 2001.

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  1. Skulking Lurker

    Skulking Lurker Registered Member

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    Why is the Farad such a large unit? It' not everyday that come across even a 1F cap.
     
    Skulking Lurker, Oct 24, 2001
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  3. Skulking Lurker

    Skulking Lurker Registered Member

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    Oops, I found out. This sounds right-


    The base units of S.I. are the metre, the kilogram, the second, the ampere, the kelvin, the mole, and the candela. These are all defined by various physical criterion.

    Clearly, no unit is going to be a handy size for all fields. The metre is way to small for astronomical work, and way too big for crystallography work. However, this is of no great consequence, because we have scientific notation. It is no great brain strain to write 3.5 x 1017 m.

    The other units are all derived from these. Some of these units are of unusual magnitudes, but again, it just means one must use scientific notation.

    It turns out that capacitance has the same dimensions as length-2 times current2 times mass-1 times time4.

    So the base unit, the Farad, equals that capacitance has the same dimensions as m-2.A2.kg-1.s4.

    This is a large unit for practical electronics, so we tend to use sci notation or the various S.I. prefixes, e.g. picoFarad, nanoFard.
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    Skulking Lurker, Oct 24, 2001
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  5. James R

    James R Just this guy, you know? Staff Member

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    1 Farad = 1 Coulomb per Volt.

    Due to the definition of the Ampere (an SI base unit), a Coulomb turns out to be a very large charge. Hence, the Farad is also a large unit.
     
    James R, Oct 24, 2001
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  7. Skulking Lurker

    Skulking Lurker Registered Member

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    Just testing
     
    Skulking Lurker, Oct 24, 2001
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  8. Reign_of_Error

    Reign_of_Error Registered Senior Member

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    1 Farad capacitors are common in very powerful car HiFi system installations!!
     
    Reign_of_Error, Oct 24, 2001
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  9. Chagur

    Chagur .Seeker. Registered Senior Member

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    Sulking Lurker ...

    Remember too that a Farad wasn't all that large when electronics depended on tubes (valves) rather than transistors.

    Take care.
     
    Chagur, Oct 24, 2001
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  10. Skulking Lurker

    Skulking Lurker Registered Member

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    Chagur: It's <font size=+3>Skulking </font>,Not sulking.
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    Skulking Lurker, Oct 25, 2001
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  11. Chagur

    Chagur .Seeker. Registered Senior Member

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    Oooops ...

    Sorry about that, mate.

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    But you must admit, 'Sulking Lurker' has a certain panache

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    Last edited: Oct 25, 2001
    Chagur, Oct 25, 2001
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