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Math Help - rearrange equation to find 2 unknowns

  1. #1
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    rearrange equation to find 2 unknowns

    can some one help with this formula please i need to find 2 unknowns
    A area and d distance

    Formula is

    C = Er*Eo*A / d

    where
    C= 100x10 power-12
    Er=12
    Eo= 8.85x10power-12

    i can isolate d/A to equal Er*Eo/C which makes d/A = 1.062 ohms

    and get d= Er*Eo*A / C


    but brain wont go any further

    any help much appreciated


    thanks Ian
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  2. #2
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    A= \frac{Cd}{E_rE_0}

    and

    d = \frac{AE_rE_0}{C}

    do you have the units for E_r, E_0 and C ?
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  3. #3
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    hello there that was a quick reply thanks!

    the units are
    C= 100pico farads
    Er is relative permittivity of 12 (ratio no units)
    Eo is relative permittivity of air 8.85x 10power-12
    A in Meters ie but very small area
    d in metres but likely around 1mm or less

    as its to do with capacitors

    thanks Ian
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  4. #4
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    Sorry Ian, a bit out of my league....
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  5. #5
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    thanks for having a go, my tutur told me to make d the subject and use that value in another equation but the question dosnt have a value for the area so im really not sure how to do it



    Regards Ian
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  6. #6
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    You still have 2 unknowns so the best you can do is make a relationship between the 2 values.

    substituting in the values given A = \frac{513}{500}d
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  7. #7
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    Thanks for taking the time m8

    back to thr drawing board i think


    Cheers Ian
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