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Homework Help: Energy stored in a LC circuit

  1. Mar 12, 2016 #1
    1. The problem statement, all variables and given/known data
    Energy in the circuit remains constant. When the current is flowing, the energy stored is all stored in the inductor. When the current stops flowing, it is because all the energy is stored in the capacitor.
    Find the fraction of energy stored in the inductor when half of the max charge is on the capacitor.

    L = inductor
    C = capacitor
    I = current

    2. Relevant equations
    1/2 *Q^2/C = U of capacitor
    1/2 * LI^2 = U of inductor

    3. The attempt at a solution

    Didn't know where to really go.

    1/2 *Q^2/C + 1/2 * LI^2 = U
    Q= .5Q
    1/8Q^2/C + x*LI^2 =U
    x= 7/8?
  2. jcsd
  3. Mar 12, 2016 #2


    User Avatar

    Staff: Mentor

    When all the energy is in the capacitor (maximum charge) there is no energy in the inductor (current is zero). So start by positing some initial total energy U and determine the maximum charge associated with it. What happens when that charge is reduced to half and current is flowing?
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