R, C, L circuits with AC Source, need help.

Discussion in 'Homework Help' started by lapoltba, Feb 1, 2009.

  1. lapoltba

    Thread Starter New Member

    Feb 1, 2009
    I am a student at RIT (Rochester institute of technology) in NY. 3rd year student in Electromechanical Technology.

    I am taking Elec. Principles I and i just cant seem to get my head around these simple RCL circuits. We have some hw problems and the teacher gave some examples but i just cant follow his method. He is a DR. and is basially brilliant so he blows people away and doesnt to a very good job explaining anythign.

    We have three series circuits one capacitive with a resistor, two inductor with a resistor (one with the resistor first and one with the inductor first)

    Given the circuits and that V= Vi Sin(wt)
    We have to:
    1. Derrive parameterized expressions for VR, VC, VL (ie. we are given no numbers) as functions of frequency (w)
    2. Draw magnitude and phase diagrams for the output voltage against normailzed (log w) scale
    3. Draw phasor diagrams for VR, VC, VL
    4. Derive parameterized expressions for Power for each circuit.

    Fun huh?

    What i understand.
    Xc(impedence for a cap) = -j(1/wc)
    Xl(impedence for an inductor) is jwl

    I know i have to use the voltage divider type deal to solve for the V. of the cap, then subtract that from the supply voltage to solve for the voltage of the resistor.

    I guess i just dont understand where to start here.... Can anyone help me out?
  2. RB211

    New Member

    Apr 17, 2007
    For the phasor diagrams the Resistor will be at 0° the Capacitor will lag by 90° and the inductor will lead by 90°.
  3. lapoltba

    Thread Starter New Member

    Feb 1, 2009

    I understand that, but i guess what i dont get is how to use the V=sin(wt) to get generic equations for the voltage of the capacitor and inductor.