1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

RC Circuit Oscillation

  1. Nov 7, 2009 #1
    1. The problem statement, all variables and given/known data
    An oscillating LC circuit has a current amplitude of 7.20 mA, a potential amplitude of 250 mV, and a capacitance of 240 nF.

    (a) What is the period of oscillation?

    (e) What is the maximum rate at which the inductor gains energy?

    2. Relevant equations
    Possibly: Energy stored in an inductor = 1/2 * L * I^2
    i = -wQsin(wt+ø)

    3. The attempt at a solution
    Energy per unit of time is Watts.

    If I find the equation for energy stored in an inductor, I can differenceate that with respect to time and find its maximum value.

    I thought that this would be:
    dE/dt = P = -L(w^3)(Q^2)sin(wt)cos(wt)

    And isn't the maximum value for this just

    (1/2)L(w^3)(Q^2) ?

    And isn't that just

    0.9 mW ?

    I've done this problem wrong several times so far, so is this one right?
     
    Last edited: Nov 7, 2009
  2. jcsd
  3. Nov 7, 2009 #2
    U = ((Q^2)/2C) cos(^2)(wt+ø) is the equation for the energy contained in the capacitor,
    not for the potential across it.
     
  4. Nov 7, 2009 #3

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    How are you determining Q? I get Q = VC = .25 *2.4e(-7) = 6e(-8) C.

    [tex]Q = VC = \int_0^{\pi/2} dQ = \int_0^{\pi/2} idt = \int_0^{\pi/2} i_{max}\sin{\omega t}dt [/tex]

    so:

    [tex]Q = VC = i_{max}/\omega[/tex]



    AM
     
  5. Nov 7, 2009 #4
    Oh, I see. I misunderstood the equation for U I had written, and therefore got a bad Q. Thanks to both.
     
  6. Nov 7, 2009 #5
    But now I have another question for this problem, and I've edited the first post for it.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: RC Circuit Oscillation
  1. RC circuits voltage (Replies: 1)

  2. RC circuit and voltage (Replies: 8)

  3. RC circuit complete (Replies: 2)

Loading...