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Response of RLC circuit i'm lost

  1. Sep 8, 2010 #1
    the problem statement is attached.

    i've begun by converting everything into phasor notation but i'm not quite sure where to go from here. when i try to add the C and the L phasors, i get zero. this doesn't seem right.
    another problem is i have no idea what to do when i get the impedances of the components added together. do i just add that to the input voltage for the answer?

    any help appreciated.
     

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  2. jcsd
  3. Sep 8, 2010 #2
    so i've converted the circuit to it's current source equivalent ( i can't remember if thats called thevenin or norton) and am able to add the impedances.

    what to do from here?

    i think i'm supposed to add the component impedances to the voltage input signal impedance and plug into v=ir for the voltage. but maybe not... i'm lost like i said. am i on the right track or far from it?
     
  4. Sep 8, 2010 #3
    Yes, you have to go into the frequency domain. From here, you can treat all the components like they're resistors with their respective impedances

    So, yeah. For your source, you have 2 at an angle -pi/4. Impedance of Res, cap and inductor are 1, -j, and j, respectively (i.e., Zc = -j/(wC))

    Now you just have to do circuit analysis from here. How can you get y(t)? Since voltages are the same in parallel, what if we combine the inductor and cap?

    -j // j = ([-j]*[j])/(j-j) = undefined.

    Well that's weird. I'm not sure what that means physically. I was going to combine those two components and then use voltage division across the equivalent impedance there. Ask your teacher about this. Maybe try to do a node equation?
     
  5. Sep 9, 2010 #4

    vela

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    What you're finding is that when ω=1000, the LC combination has infinite impedance because that's the resonance frequency of the circuit. No current can flow, so the entire input voltage appears at the output.
     
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