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Resistors and capacitors

  1. Sep 19, 2005 #1
    I got a question that reads: Supoose a 10khz signal with an amplitude of 1 volt is applied across a 1k(ohm) trdidyot snf s 0.25 microF capacitor which are connected in series. What is the voltage drop across the capacitor?

    I tried to use the equation Vc(t) + Vco*cos(omega*t) in which i got 1*cos(2*pi*10000*0.0025) in which i got -.92104. I don't think this is right, but i am not sure.
     
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  3. Sep 19, 2005 #2

    Tom Mattson

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    Help me get this straight: You've got a single loop circuit with a voltage source, a resistance, and a capacitance, is that it?

    If that's the case then you can write down Kirchhoff's voltage law for the loop. You'll have a first order differential equation which you can solve for the capacitor voltage.
     
  4. Sep 19, 2005 #3
    so the answer would be 1 since i would do 1volt(1kohms/1kohms)=1v?
     
  5. Sep 19, 2005 #4

    Tom Mattson

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    Think about what you've just said. You've got a capacitor with a resistance hooked up to a time-varying voltage source. How can you have a constant voltage across the capacitor in that case? (Answer: You can't.)

    Am I correct in my assumption about the setup of this circuit?
     
  6. Sep 19, 2005 #5
    yes i beleive you are correct. I copy the question just like it is in my pre lab.
     
  7. Sep 19, 2005 #6

    Tom Mattson

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    OK, in that case you need to do what I said earlier. Write down Kirchhoff's voltage law for the circuit and solve the resulting differential equation. You will also need to know some initial condition for the circuit (like the initial capacitor voltage).
     
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