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: Using Kirchoff's Laws to solve a circuit

  1. Feb 25, 2007 #1
    1. The problem statement, all variables and given/known data

    Find i, i1, i2 in terms of V, r, R, c, and t on the following circuit:

    problem.jpg


    2. Relevant equations

    I suppose I would use Kirchoff's law for this...


    3. The attempt at a solution

    i = i1 + i2
    -ir + V – i1R = 0
    -ir + V – Vc = 0

    Vc = V – ir = q/c
    i1R = -ir + V

    Where do I go from here?
     
  2. jcsd
  3. Feb 25, 2007 #2
    Following the path with just the resistor and the capacitor can I reduce the current to the equation: i2 = (V/r)e^(-t/rC)
     
  4. Feb 25, 2007 #3

    Mentz114

    User Avatar
    Gold Member

    After the transient current that charges the capacitor has gone, you have 2 resistors in series so

    V = i ( r + R)

    You can get the transient by calculating the voltage across R.
     
  5. Feb 25, 2007 #4
    This is what I'm currently thinking...

    i= [V/(r+R)](1-e^-(t/rC))+(V/r)e^-(t/rC)
    i1= [V/(r+R)](1-e^-(t/rC))
    i2= (V/r)e^-(t/rC)
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook