Finding the Energy in Capacitor?

Discussion in 'Homework Help' started by Digit0001, Apr 3, 2011.

  1. Digit0001

    Thread Starter Member

    Mar 28, 2010
    89
    0
    Hi

    I am having trouble with the following question:
    View attachment tut4qns.doc


    For the first question i got the answers for a) however the energy for the 20 and 40 micro ohms capacitors are incorrect.

    This is what i did:

    sub 0.5 into the equations that i got for a) and i get
    v1 = 840.150v
    v2 = 208.030v

    w_12 = 0.5 * (12 * 10^-9) * v1^2
    =4.23J

    w_20 = 0.5 * (20 * 10^-9) * v2^2
    =0.424J

    w_40 = 0.5 * (40 * 10^-9) * v2^2
    =0.866J

    Question 2 how would i start it?

    P.S
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    A hint for (2) is to equate the equations of the energy of the capacitor with the energy of the inductor to find a relationship between the voltage across the capacitor and the current though the inductor. Also, at steady state the voltage across the inductor is zero and the current through the capacitor is zero.
     
  3. Digit0001

    Thread Starter Member

    Mar 28, 2010
    89
    0
    what about my first question what have a done wrong?
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    You've got the wrong value for V2. It should be 178V.
     
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