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: Voltage on capacitor

  1. Oct 28, 2012 #1
    A 22 nF capacitor is initially charged to 10V. It is then discharged by connecting a 100k resistor across it. Approximately how long does it take for the voltage on the capacitor to fall by 10%?



    v = v₀e^(–t/τ)
    RC = τ = time constant



    Im not sure if this the right equation what do you think guys?
     
  2. jcsd
  3. Oct 28, 2012 #2

    gneill

    User Avatar

    Staff: Mentor

    The equation looks fine. How you make use of it is what's important :smile:
     
  4. Oct 28, 2012 #3
    τ = 22nF x 100k = 2200µs = 2.2 ms

    then
    v/v₀ = 0.9 = e^(–t/2.2m)
    –t/2.2m = ln 0.9 = –0.1054
    t = 0.0002318 = 232 µs <-- answer!

    is that alright?
     
    Last edited: Oct 28, 2012
  5. Oct 28, 2012 #4

    gneill

    User Avatar

    Staff: Mentor

    Yes, that's fine.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook




Loading...