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!

Discharging circuit

  1. Apr 1, 2009 #1
    1. The problem statement, all variables and given/known data
    http://online.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?courses/phys212/oldexams/exam2/fa06/fig17.gif [Broken]
    After a very long time with both switches in the closed position, switch S2 is reopened. How long does it take for the charge on capacitor C2 to drop to 1/e (36.8%) of its fully-charged value (i.e. of the value it had just before S2 was reopened)?


    2. Relevant equations
    Time constant = RC
    capchg7.gif

    3. The attempt at a solution
    I try to find the total resistance, but am not sure how. I am not even sure what it means by "drop to 1/e (36.8%)". Does it mean 36.8% of the total charge?
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 1, 2009 #2

    Pythagorean

    User Avatar
    Gold Member

    yes, since charge is a function of voltage here. As the voltage drops, less charge is accumulated on the plates of the capacitor.
     
    Last edited by a moderator: May 4, 2017
  4. Apr 1, 2009 #3
    Okay, to find the time constant, RC, I have to find the equivalent resistor at that point. But I don't know how? With only S2 reopened, are all the resistors now in parallel?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Discharging circuit
  1. Discharging a circuit (Replies: 1)

  2. Discharging RC circuit (Replies: 7)

Loading...