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!

RC circuit final charge

  1. Feb 10, 2009 #1
    1. The problem statement, all variables and given/known data
    Consider an RC circuit in which a capacitor is being charged by a battery connected in a circuit. Initially the capacitor is uncharged. Then the switch is closed.
    After a time equal to 4.5 time constants, what percent of the final charge is present on the capacitor?

    2. Relevant equations
    Q = Qo [1 - e^ (-t/RC)]

    3. The attempt at a solution

    I picked a value of 100 for Qo
    Q= 100 [1 - e^ (-t/4.5)]
    my approach was going to be to find Q and then see wht percent that is of the initial charge Qo
    but I dont know wht to put in for the time "t"
    please help me out
  2. jcsd
  3. Feb 10, 2009 #2


    User Avatar
    Homework Helper

    I think you would take t = 4.5RC
  4. Feb 10, 2009 #3
    so for the expression e^(-t/RC) I do e^(-4.5) ?
  5. Feb 10, 2009 #4


    User Avatar
    Homework Helper

    4.5 time constants means a time of 4.5*R*C.
    R*C comes out in units of time.
  6. Feb 10, 2009 #5


    User Avatar
    Homework Helper

    Yes that should do it.
  7. Feb 10, 2009 #6
    Awsome! Thank you so much!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: RC circuit final charge
  1. Charging RC circuit (Replies: 11)