Please help with this proplem

Discussion in 'Homework Help' started by tinhnho, Oct 31, 2004.

  1. tinhnho

    Thread Starter Active Member

    Aug 31, 2004
    34
    0
    hi everyone

    Please help me this proplem

    The voltage source in the figure below has a step increase at t =0 . For t<0, vs(t)=0 while for t>0, vs(t) = 1V
    Find v1(0-), v2(0-), v1(0+), v2(0+), v1(infinite), v2(infinite)

    i have found v1(0-)=0 and v2(0-)=0 , but just confuse how to find v1(0+), v2(0+), v1(infinite), v2(infinite), could anyone please give me some ideas ? thanks alot
     
  2. haditya

    Senior Member

    Jan 19, 2004
    220
    0
    at 0+, the caps act like shorts while inductors acts like open ckts.... therefore the ckt reduces to a voltage divider of R1&R3.. v1=v2=0.5V

    at t=infinite, the caps are open, the inductors short, the V2=0
    and v1=0.6666V

    jus verify the answers of u hav em
     
  3. tinhnho

    Thread Starter Active Member

    Aug 31, 2004
    34
    0
    VEry thanks for those comments. Sorry that i still have other question which just like to verify with you. Please see these pictures below

    Question:

    The current source in the figure below has a step increase at t =0 . For t<0, Is(t)=0 while for t>0, is(t) = I0. The circuit is "dead" before t = 0, so v(0-)=Ic(0-)=Ir(0-)=iL(0-)=0

    a) Find v(0+), Ic(0+), Ir(0+), IL(0+), Symbolic answers( formulas)


    B) Find dv/dt at t =0 symbolic answer( formulas)

    Here is the answer for both a) and b) in the picture number 2 from left to right
     
  4. haditya

    Senior Member

    Jan 19, 2004
    220
    0
    i think
    ic(0+)= Is, Ir=0, Il=0...ie the cap acts like short
    why do u say Ic=-Is??
    V(0)=0
    V=C*(integral)Ic(t)dt
    dv/dt eludes me
     
  5. tinhnho

    Thread Starter Active Member

    Aug 31, 2004
    34
    0
    sorry, i think they were
    Ic = C(dv/dt)
    Ir= -Is

    now it's confusing me :(
     
  6. tinhnho

    Thread Starter Active Member

    Aug 31, 2004
    34
    0
    thanks, i got it figured out
     
Loading...