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Homework Help: Max Harge on a Capacitor in LC Circuits

  1. Apr 3, 2012 #1
    1. The problem statement, all variables and given/known data
    An oscillating LC circuit consisting of a 1.2 nF capacitor and a 3.3 mH coil has a maximum voltage of 2.6 V.
    (a) What is the maximum charge on the capacitor?

    2. Relevant equations

    3. The attempt at a solution
    I tried Q=CV but this did not work I got the answer 3e-9 when I plugged in but this did not work. I have also tried doing it the long way by solving for energy using .5Li^2 = .5CV^2 then solving for i. Then I solved for w by using ω=1/(√LC) and the solved for the period by using T=2∏/ω which after you find it you can divide by 4 to get time when you can plug in time, angular frequency, and current max to the equation I(max) = -ωQ(max)sin(ωt) this gave me 3e-9 as well which is not correct. The numbers I got for I(max) = .00155692, ω=502518.9076, time=.000003126. Finally I have tried this which I found online Q=(energy of capcitance)V this gave me 1e-8 this did not work either. I double checked the numbers in my calc and they were correct I dont understand!!
  2. jcsd
  3. Apr 3, 2012 #2


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    Staff: Mentor

    Is it possible that you're being tripped up by required significant figures? Was your charge really 3E-9, or should it be 3.1E-9?
  4. Apr 3, 2012 #3
    I am gonna try another calulator mine seems to be off
  5. Apr 3, 2012 #4
    LOL thanks man that worked and I checked it with a new calc.
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