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: Signal flow graph, describing a RC circuit?

  1. Jul 8, 2012 #1
    Signal flow graph, describing a RC circuit?

    Hi, guys. This is my first post on this forum!
    I'm trying to understand this example in my textbook.
    The current and voltage equations are:
    where G=1/R, Z(s)=1/Cs, and I1(s)=I1
    Then the text says the following signal flow graph can be obtained:
    And finally we can somehow obtain the transfer function:

    First question, why is it necessary to do the substitution for G, Z(s) and I1?
    For the fourth equation, it says V3=I2Z, where Z(s)=1/Cs. Therefore, V3=I2/Cs (voltage=current/capacitance)? Where does this relationship comes from?
    Lastly, how do I know how many equations do I need? And which circuit elements should I describe?

    I might have more questions later, but I couldn't proceed without know the basics.
    Thank you so much!
  2. jcsd
  3. Jul 9, 2012 #2
    V3 = I2Z , where Z(s) = 1/Cs this is because voltage across capacitance is given as CdV/dt=I thus taking laplace transform on both the sides we get sC*V(s)=I(s)
    and V(s)=I(s)/sC therefore V3=I2/Cs.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook