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Instantaneous Current

  1. Oct 22, 2009 #1
    1. The problem statement, all variables and given/known data
    The quantity of a charge passing through a surface of area 2.67 cm^2 varies with time as q=q1t^3 + q2t + q3, where q1=4 C/s^3, q2=4.5 C/s, q3=9.5 C and t is in seconds. What is the instantaneous current through the surface at t=1.2s? Answer in units of A

    2. Relevant equations

    3. The attempt at a solution
    I found that dq/dt = 12C/s^3t^2 + 4.5C/s

    To find I, I need to plug in t. Which gives me (12C/s^3)(1.2s) + 4.5C/s, however I am unsure of how to do the conversion to come to the right answer. I know that 1A = 1C/s. I plugged in 25.236 A in but it came out wrong. I know there is some conversions I am missing, any pointers? Thanks
  2. jcsd
  3. Oct 22, 2009 #2


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    Homework Helper

    (12C/s^3)(1.2s) + 4.5C/s
    Check the substitution.
  4. Oct 26, 2009 #3
    I got it. Thanks for pointing that out, its amazing how the simple mistakes always get you.
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