Modelling the Charging of a Capacitor

Discussion in 'Homework Help' started by Sci, Feb 25, 2005.

  1. Sci

    Thread Starter New Member

    Jan 21, 2005
    8
    0
    I consulted some text books, which gave me what I attached as a screenshot, for dv/dt of a capacitor from the time it is just to be about charged. To cut a long story short, I'm suppose to model it using the analytical equation and Euler's method. However the voltage DE I got from the text book itsn't working out. It says:

    (dv/dt) = (v - Vs) / RC,
    where v is the voltage across the cap, and Vs is the applied voltage. Using this equation makes me end up with a neg, or just wrong voltage as opposed to the corrent analytical equation of

    v = Vs (1 - e^(-t/RC) )

    What's the proper DE?
     
  2. hgmjr

    Retired Moderator

    Jan 28, 2005
    9,030
    218
    Is it possible that you overlooked the negative sign in the expression shown in your screenshot.

    It reads dv/dt = - (v-Vs)/RC. This is equal to dv/dt = (Vs-v)/RC.

    Hope this help?

    Good Luck.
     
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