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Finding resistane and current non-ohmic

  1. Mar 27, 2014 #1
    1. The problem statement, all variables and given/known data
    A 10.0-μF capacitor is charged by a 10.0-V battery through a resistance R. The capacitor reaches a potential difference of 4.00 V at the instant 3.00 seconds after charging begins
    1.) Find R
    2.) Find the current at t=3.00 seconds after charging begins.


    2. Relevant equations
    i=[itex]\frac{dq}{dt}[/itex]=-[itex]\frac{CV_{ab}}{RC}[/itex]e[itex]^{-t/RC}[/itex]


    3. The attempt at a solution
    so obviously I know how to find current but I need to find resistance and I cannot use R=V/I because it is non-ohmic! what do I do?
     
  2. jcsd
  3. Mar 27, 2014 #2

    gneill

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    Staff: Mentor

    Find the time constant ##\tau = RC##. You know C....
     
  4. Mar 27, 2014 #3
    why am i using time constant?
     
  5. Mar 27, 2014 #4

    gneill

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    Staff: Mentor

    Read the question carefully. Some information you're given involves time. If you can find the time constant RC and you already know C then...
     
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