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Homework Help: Circuit Problem: Stored Energy

  1. Dec 14, 2008 #1
    1. The problem statement, all variables and given/known data
    We are given: R1= 1[tex]\Omega[/tex]
    R2= 2[tex]\Omega[/tex]
    L = 3 mH
    C = 500 [tex]\mu[/tex]F

    If the voltage is kept at 4V what is the energy stored in the circuit after it has reached a steady state. There is a link posted to the circuit provided below.

    2. Relevant equations
    energy stored in capacitor = 1/2Cv2
    energy stored in inductor = 1/2Li2

    3. The attempt at a solution

    Since you are given all the values you can just plug into the formula to find the energy stored in the capacitor. I got 0.004J. For the inductor I determined the current that flows through it which is 4V / 2[tex]\Omega[/tex] = 2A. I then used this value to compute the energy stored in the inductor, for that I got 0.006J. The total energy would be the sum of the two.

    This seems to be a simple problem but I'm just wondering if its a trick question since they want to know what the energy stored is after a long period of time.

  2. jcsd
  3. Dec 14, 2008 #2
    The energies (1/2)Li^2 and (1/2)Cv^2 are the steady state values for stored energy. You're result looks correct to me.
  4. Dec 14, 2008 #3
    Great thanks.
  5. Dec 15, 2008 #4


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    Steady state means after an infinite time. Generally we consider that after 5 time constants the circuit reaches steady state. That is the meaning of a long period of time
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