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30 September, 07:08

When two capacitors are connected in parallel across a 12.3 v rms, 1.46 khz oscillator, the oscillator supplies a total rms current of 560 ma. when the same two capacitors are connected to the oscillator in series, the oscillator supplies an rms current of 124 ma?

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  1. 30 September, 07:25
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    3.32µF and 1.64µF

    Since, you haven't actually asked a question, I am going to make a guess on what the question is based upon the data provided. My educated guess is "What are the values of the two capacitors?"

    The formula for the Capacitive reactance is

    X = 1 / (2*pi*f*C)

    where

    X = reactance

    f = frequency

    C = capactance

    Let's solve for C

    X = 1 / (2*pi*f*C)

    CX = 1 / (2*pi*f)

    C = 1 / (2*pi*f*X)

    Now with the capacitors in parallel, we have a reactance of:

    I = V/X

    IX = V

    X = V/I

    X = 12.3/0.56

    X = 21.96428571

    So the capacitance is:

    C = 1 / (2*pi*f*X)

    C = 1 / (2*pi*1460*21.96428571)

    C = 4.96307x10^-6 = 4.96307 µF

    And with the capacitors in series we have a reactance of:

    X = V/I

    X = 12.3/0.124

    X = 99.19354839

    So the capacitance is:

    C = 1 / (2*pi*f*X)

    C = 1 / (2*pi*1460*99.19354839)

    C = 1.09896x10^-6 = 1.09896 µF

    Now we can setup two equations with 2 unknowns.

    4.96307 = x + y

    1.09896 = 1 / (1/x + 1/y)

    y = 4.96307 - x

    1.09896 = 1 / (1/x + 1 / (4.96307 - x))

    1.09896 = 1 / ((4.96307 - x) / (x (4.96307 - x)) + x / (x (4.96307 - x)))

    1.09896 = 1 / (((4.96307 - x) + x) / (x (4.96307 - x)))

    1.09896 = 1 / (4.96307 / (x (4.96307 - x)))

    1.09896 = x (4.96307 - x) / 4.96307

    5.45422 = x (4.96307 - x)

    5.45422 = 4.96307x - x^2

    0 = 4.96307x - x^2 - 5.45422

    0 = - x^2 + 4.96307x - 5.45422

    We now have a quadratic equation. Use the quadratic formula to solve, getting roots of 3.320460477 and 1.642609523. You may notice that those 2 values add up to 4.96307. This is not coincidence. Those are the values of the two capacitors in µF. Rounding to 3 significant figures gives us 3.32µF and 1.64µF.
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