Need help with basic capacitance question.

Discussion in 'Homework Help' started by sini, Mar 19, 2011.

  1. sini

    Thread Starter New Member

    Jun 28, 2010
    6
    0
    Hello, I did all the questions in the book(Fundamentals of Electric Circuits, 4th edition) regarding the capacitance except this one which has me stumped.

    Q6.2
    A 20e-6 F capacitor has energy w(t)=10cos^2(377t) J. Find current.
    Now I know that if I differentiate w(t) i'll get power(p=dw/dt) which equals vi, but I can't get v anywhere. I also can't use Q=CV since there is no where to get Q from.
    I'm guessing the book made a mistake and meant to say v(t) not energy, or I'm missing something huge here. :confused:
     
  2. syed_husain

    Active Member

    Aug 24, 2009
    61
    5
    there is another formula: energy of a capacitor,w = 0.5*C*v^2. from this u can calculate voltage. the rest u already know.

    cheers.
     
    sini likes this.
  3. sini

    Thread Starter New Member

    Jun 28, 2010
    6
    0
    bleh thanks, must have been really tired last night lol
     
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