1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: AC Nodal Voltage V(t)

  1. Nov 3, 2012 #1
    1. The problem statement, all variables and given/known data
    I've attached the question. Nodal Voltage question.png
    So I'm not sure which method should be used to solve this. I was thinking superposition, but the voltage supplies are are both at the same ω value.

    2. Relevant equations
    v(t) = Vmaxcos(ωt + [itex]\phi[/itex])
    ZL = jωL
    ZC = 1/jωL
    3. The attempt at a solution
    convert everything to phasor form
    Vs1 = 20[itex]\angle[/itex]0°
    Vs2 = 20cos(1000t - 90°) = 20[itex]\angle[/itex]-90°
    10mH = j10 = 10[itex]\angle[/itex]90°
    0.1mF = -j10 = 10[itex]\angle[/itex]-90°

    Then I'm not really sure what to do next, do I use superposition or mesh analysis or etc. and then how does that work with phasors?
    So would appreciate a push in the right direction.
  2. jcsd
  3. Nov 3, 2012 #2


    User Avatar

    Staff: Mentor

    Since you have marked all node voltages, you could use: current through the inductor + current through the capacitor = current in the resistor
    and with only one unknown, solve this to find Vx
  4. Nov 4, 2012 #3

    rude man

    User Avatar
    Homework Helper
    Gold Member

    In terms of phasors, you can let Vs2 = 20, then Vs1 = 20ejπ/2.

    You can then solve using kvl or you can use superposition to solve for one of the sources at a time, then add the results.

    Superposition is allowable if the sources are independent, which here they are.

    Had the frequencies been different you would have had to use superposition, solving two separate problems individually, with different complex impedances for each problem. Superpositoon would have to be done in the time domain.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook