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: Capacitor Equations

  1. Jun 17, 2017 #1
    1. The problem statement, all variables and given/known data
    Hi, i've run into two different equations for the voltage of a typical RC circuit, one resistor, and one capacitor.
    Please explain the different between the two. One has a 1 - the natural log and the other one doesnt.

    2. Relevant equations
    1. V(t) = Vo*e^(-t/RC)

    2. Vc = Vs(1-e^-t/RC)

    3. The attempt at a solution
  2. jcsd
  3. Jun 17, 2017 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    One of the equations is for a charging capacitor and the other for a discharging capacitor. To figure out which is which, evaluate each expression at t = 0 and at t → ∞ .
  4. Jun 17, 2017 #3
  5. Jun 18, 2017 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    It is not a log; it is a negative exponential.
    Do you understand what these two curves look like?
  6. Jun 18, 2017 #5
    Typo, yes it is the natural exponent. I dont know why but i was thinking exponent and typed log. They are inverse of each other.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted