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Homework Help: Unknown Simple RCL Circuit

  1. May 8, 2012 #1

    I'm trying to determine a simple RCL circuit from the output at the terminals. I have two unknown circuits and I'd just like to get a confirmation about if I'm heading in the right direction with this.

    The circuit can only be a combination of a single resistor and/or a single capacitor and/or a single inductor.

    Unfortunately the results are incomplete as well, so I've given my knowledge about the circuits where this is the case.

    Circuit A:
    DC Results: 10V DC input, results measured over terminals of unknown circuit.
    4.2 mA

    AC Results: Voltage source varies
    @ 4.96kHz with 9.2V input
    Voltage source and voltage over terminal are in phase.
    Voltage over terminal: 172mV

    @ 5.476kHz with 9V input
    Phase difference: 9.2μs No information about leading peak
    Voltage over terminal: 256mV

    @ 4.505kHz with 9V input
    Phase difference: 14μs No information about leading peak
    Voltage over terminal: UNKNOWN

    [STRIKE]This circuit is likely to either be a resistor in series with a parallel capacitor and inductor.
    [/STRIKE] URfyE.png

    I am now fairly certain that Circuit A is instead in this configuration:
    Due to the relationship between V and R, which is inversely proportional with the new circuit config and more linear for the one above it. When looking at the DC results you can see that the resistance is high, however the voltages for the AC analysis is low.
    Can anyone confirm this logic for me?

    Circuit B:
    DC Results: 10V source, results measured over terminals of unknown circuit.
    ∴ Circuit has a capacitor in series.

    AC Results: Voltage source varies
    @ 33Hz with 4.72V input
    Phase difference: Source(7.720ms) - Unknown circuit(2.12ms) = 5.6ms
    Voltage at terminals: 17.6mV

    @ 714.3Hz
    In Phase

    @ 51.89Hz
    Phase difference:Unknown circuit(4.90ms) - Source(2.08ms) = 2.9ms
    Voltage at terminals: 46.8mV

    B conclusions:
    - Not purely reactive, energy is dissipated.
    - In phase @ >714.3Hz
    - Source is the leading phase for 33Hz
    - Unknown circuit has leading phase for 51.89Hz
    ∴ Circuit could be one of the two:


    Does anyone have any idea how I would discern from these which was the circuit? Or if I would need more information to be able to proceed?

    Last edited: May 9, 2012
  2. jcsd
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