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.

 

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.

 

bleh thanks, must have been really tired last night lol