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Homework Help: RC Circuit Analysis

  1. Nov 24, 2013 #1
    1. The problem statement, all variables and given/known data

    Use current equation and find di/dt expression, hence show if initial gradient were maintained the current would be 0 after 1 time constant.

    2. Relevant equations

    I calculated RC to be 0.5s i=0.02e^-t/0.5

    3. The attempt at a solution

    I solved di/dt to be


    i'm stuck where to go next though, can anyone help? Thanks :)
  2. jcsd
  3. Nov 24, 2013 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    We are not mind readers, please post a COMPLETE problem description and show us your work.
  4. Nov 24, 2013 #3
    Sorry I didn't realise it was linked.The initial circuit was an RC circuit with 100v source in series with a 100uf capacitor and 5kohm resistor.I was then tasked with graphing i vs t for the first 3 seconds and drawing it.After 3 seconds i=5*10^-5

    The formula for i was given as 0.02e^-2t

    Then calculated CR to be 0.5

    Then I had to draw a tangent and estimate the gradient which came out at 0.02/-1.1=-0.018

    Then came the question that was asked, hope that helps.
  5. Nov 25, 2013 #4


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    Staff: Mentor

    You differentiated to find the general equation for gradient as a function of time? Well, when you need to know the gradient at some time t1 you simply substitute the value of t1 for t in your general equation for gradient.

    Initial gradient is usually the gradient when t = 0 secs.
  6. Nov 26, 2013 #5
    Thanks, so the gradient would be -0.04, so after 0.5s( one time constant) the current will have dropped by 0.02, so the current will be 0 after one time constant.

    Thanks so much for your help. :)
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