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Electricity - Total Charge

  1. Feb 15, 2005 #1
    An electric current is given by the expression I ( t ) = 115 sin(120t), where I is in amperes and t is in seconds. What is the total charge carried by the current from t = 0 to t = 1/120 s?

    >> Since I = deltaQ/deltaT I rearranged and solved for Q = I(deltaT).

    Then I took T=0 and plugged it into the I formula they gave. Then I plugged T=1/120 into that formula. And subtracted the two answers to get 0.008362. Then I tried taking this answer and multipling it by (1/120) to get Q. I don't think I did this right, but I don't really know how to go about finding the right answer :(

    Any ideas?
  2. jcsd
  3. Feb 15, 2005 #2

    Doc Al

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    Staff: Mentor

    I presume (120t) is in radians?

    I presume you integrated?

    What formula? All you needed to do was integrate over given range.
  4. Feb 15, 2005 #3
    ? I'm confused on what I'm supposed to integrate -> the original I(t) that they gave me? Won't that just give me the current when they want the charge?
  5. Feb 15, 2005 #4

    Doc Al

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    Staff: Mentor

    Since the current is the time derivative of charge ([itex]I = dQ/dt[/itex]), the charge is the integral (anti-derivative) of the current:
    [tex]dQ/dt = 115 sin(120t)[/tex]
    [tex]dQ = 115 sin(120t) dt[/tex]
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