1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Second order circuit need some confirmation on the steps involved.

  1. Mar 10, 2013 #1
    1. The problem statement, all variables and given/known data
    Find v(t) for all t>0. Use second order method.

    2. Relevant equations

    3. The attempt at a solution
    Before the switch is closed:
    solving for i:

    From node v(t):
    [C dv(t)/dt] + i(t) + [V(t)/4] + [(v(t)-80i)/80]+[(v(t)-80)/160] = 0

    v(t)=L di(t)/dt

    Later on solve the 1st equation for i(t), then substitute into KVL equation.

    Attached Files:

    • 1.jpg
      File size:
      13.9 KB
  2. jcsd
  3. Mar 10, 2013 #2


    User Avatar

    Staff: Mentor

    Consider replacing everything before the switch with a Norton equivalent.

    Have you learned about Laplace transforms yet?
  4. Mar 10, 2013 #3
    yes, but the question ask us to use 2nd order to solve it.
    Do we need to take in account for the dependent source?
    we convert it to 80*0.25=20V
  5. Mar 10, 2013 #4


    User Avatar

    Staff: Mentor

    In my opinion, I don't think that using Laplace transforms to solve the differential equation would be cheating...
    Yes, the dependent source makes a difference, but you may be surprised by the resulting Norton equivalent. The Norton equivalent should have a current source in parallel with a resistance; 20V is not a current (nor is the the correct Thevenin voltage).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted