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RLC circuit resistance, inductance and capacitance

  1. May 16, 2012 #1
    A series RLC circuit connected to a 100-V 60-Hz source draws a current of 2.5 A. The
    measured power factor for the circuit is 0.7 leading, and the inductive reactive power is
    300VAr. Calculate the resistance, inductance and capacitance of the circuit and show the
    corresponding impedance diagram.
     
  2. jcsd
  3. May 16, 2012 #2

    psparky

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    Cool problem, but we can't answer you unless you show some effort or work. Also, this looks like it belongs in the homework section.........

    Also, the power factor for inductive ciruits are lagging! PF's for capacitive circuits are leading!
     
  4. May 16, 2012 #3
    In a series circuit don't we take the current to be the reference direction.
    This means that Voltage leads the current in an inductive circuit and voltage lags the current in a capacitative circuit.
    I think this is correct !!!!
     
  5. May 16, 2012 #4

    psparky

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    Almost...but voltage is always your reference point because it's generally set. And the reference point for the voltage is set at zero degrees.

    So in inductive circuits....we say that current lags the voltage.

    In capacitive circuits....we say that current leads the voltage.

    And I would show you the math but I'm getting tired of explaining caps and inductors.

    Perhaps a section should be dedicated to this obviously gigantic topic that most people understandably struggle with.
     
    Last edited: May 16, 2012
  6. May 16, 2012 #5
    In all of my text books for SERIES RLC circuits the current phasor is drawn at 0 degrees (horizontal) because the current is the same through each component. The voltage phasors are then drawn vertical(+) for inductor and vertcal(-) for capacitor and horizontal for resistor.
    In a way it does not matter what you say when you use leading and lagging as long as you make clear the reference phasor. V leading I means exactly the same as I lagging V.
    It makes sense to use leading for inducatance and lagging for capacitance when referring to voltage because this matches DC behaviour when a switch is closed.
    In my teaching the exam board even suggest a mnemomic to remember CIVIL.....I is behind V for a capacitor and V is ahead of I for an inductor.
     
  7. May 16, 2012 #6

    psparky

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    I see what you are saying......

    But since the voltage is set in a circuit....and the current and the resistances are the variables......Voltage is generally the set point.

    Also, in general conversations with engineers and PHD's.....it is generally put the way I put it.

    But....perhaps you are from overseas or something....I'm in USA. Oh....and I see you are a physics major.....that's probably the difference in our opinions.

    You are not wrong in what you are saying, I've just never heard it put that way before.
     
  8. May 17, 2012 #7
    worth looking at HyperPhysics (Georgia state university) for guidance in this area
    Infinetly better than Wiki and used as an excellent reference source for physicists. I use it all the time.
     
    Last edited: May 17, 2012
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