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RLC Series Circuit

  1. Oct 23, 2003 #1
    I just finished an exam and this problem gave me fits. It seemed simple enough when I first looked at it, but it took me a while to come to the following conclusions which I'm not sure are correct.

    The problem had an RLC series circuit with source of 141.4 Volts peak and a frequence of 1 kHz. The RMS voltage over the inductor is 100 volts and the RMS voltage over the capacitor is 40 volts.

    I needed to find the RMS voltage over the resistor, the power factor and draw a phasor diagram of the voltages.

    This is my reasoning and boy do I hope it's correct:

    Since it's a series circuit the current is the same through all the components. Therefore, can't I use a phasor diagram to find Vrms over the resistor.

    The voltage of the inductor would have a phase angle of 90 degrees and the voltage of the capacitor would have a phase angle of -90 degrees, so on the y-axis (complex axis) I'd have a vector 60 volts long and on the x-axis (real axis) I'd have the 100 rms volts from the source or would I have the unknown Vrms of the resistor?

    Argh! I put the 100 volts rms for the source on the x-axis, but now I'm thinking it should have been the unknown Vrms over the resistor.

    Too tired to think about out it right now, but I'd really appreciate some input.

  2. jcsd
  3. Oct 23, 2003 #2
    Yup, after considerable thought. The voltage for the resistor should have been on the x-axis, not the voltage for the source. I guess I was confused by the fact that you usually use the source voltage with a phase angle of 0 as your reference point.

    Anyway it all comes back to me now. (too little too late for my exam).

    Thanks anyway.
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