Basic Second Order Transient Circuit (RLC)

Discussion in 'Homework Help' started by wiz0r, May 2, 2008.

  1. wiz0r

    Thread Starter Active Member

    May 2, 2008
    64
    0
    Hello,

    I'm having problems with this circuit. I'm trying to solve this problem, but I'm stuck right now. Okay, well, I'm trying to figure out if this is a Parallel RLC or a Series RLC (we have not cover series + parallel RLC circuits on my class). Seems to me that it is a series+parallel RLC, tho.

    The circuit is on the picture. First, I turn off the sources, and try to find the equivalent resistence. What I do is:

    R12 = (R1 * R2) / (R1 + R2) = 3/2

    R123 = R12 + R3 = 11/2

    Now, how can I add R4 to R123? It doesnt seem to be in series, or parallel. Am I doing something wrong? Please help, I know this is a stupid/easy question, but bleh, I don't know what I'm doing wrong. Unless, this is a series + parallel RLC circuit?

    Sadly, I can't continue doing the exercise, 'cause of this little problem. Can someone help me?

    Any help will be greatly appreciated.

    ~wiz0r
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63

    if you remove the voltage source by a short and the current source by an open circuit, thus remove them, then R4 is in series with R123.
     
  3. wiz0r

    Thread Starter Active Member

    May 2, 2008
    64
    0
    thanks alot, mike.

    Now I know that R4 is in series with R123. But, I supposed I did something wrong before that.

    the α(series) = Req / (2*L)

    which according to our professor, α(series) should be 0.5.

    according to my calculations;

    Req = R123 + R4 = 15/2

    therefore;

    α(series) = (7.5) / (2*2) = 1.875

    Obviously, 0.5 != 1.875

    So, can anyone please tell me what am I doing wrong, or where is my mistake? anyone?

    again, any help will be greatly appreciated.

    EDIT: Well, I supposed I did a little mistake when I drew the circuit. The closed switch should look like .---->. instead of having that 45 angle. I don't know if it matters or not, so yea..
     
  4. wiz0r

    Thread Starter Active Member

    May 2, 2008
    64
    0
    mm, well, i figured out what was wrong.

    since the switch is closed, i need it to open it to find the equivalents R, L, and C to check if its an series RLC or parallel RLC.

    i opened the switch, and took out the sources, everything cancels out, and i'll have only the rightmost loop with the 2 ohm resistance, 2H inductance, and 1F capacitance.

    anyway, could somone tell me if im right or not?
     
Loading...