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Help with integration

  1. Feb 5, 2012 #1
    hello all new to the forum i have a calculus problem wonder if anyone can help the charge (q) can be obtained by intergrating (i) with respect to time determine the the charge on capacitor as a result of current flowing for three hundredths of a second if (i) is a constant 5mA, my calculus is very rusty but have i got the equation right
    ∫ 5 di which i get the answer to 23.5 if im doing it right.

    Any help would be great thanks.
  2. jcsd
  3. Feb 5, 2012 #2


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    Staff: Mentor

    Welcome to the PF.

    IF the current i is constant, you don't need to use integration. You only need to use integration if i varies with time...
  4. Feb 5, 2012 #3
    ah ok so q = integral of (idt) is that right
  5. Feb 5, 2012 #4


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    Staff: Mentor

    Again, since i(t)=constant, you don't need the integral. You just multiply.

    The fundamental equation for when the current is constant is

    i(t) = ΔQ / Δt

    So the change in charge with time is constant if I(t) is constant. What multiplication should you use to find the charge accumulated on the capacitor in a time Δt?
  6. Feb 6, 2012 #5
    ok thanks for your help.
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