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Homework Help: Carbon Dating

  1. Apr 13, 2010 #1


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    The problem statement, all variables and given/known data
    The half life of carbon 14 is 5730 years long. Assume that dQ/dt = -rQ. Determine the constant rate r.

    The attempt at a solution

    dQ/dt = -rQ (Given)

    dQ/Q = -rdt (algebra)
    lnQ = -rt (integrate)
    -lnQ/t = r (algebra)

    How do I work in 5,730? Also, did I do the equations correctly?
  2. jcsd
  3. Apr 14, 2010 #2


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    Homework Helper

    I think you have forgotten a constant in your inetgration if it is an indefinite integral, otherwise integration looks ok

    to get r
    start with Q = 1 at t = 0
    then by the meaning of half life, you have Q = 1/2 at t = 5730yrs

    Another option is to re-perform the integration as a definite integral from t=0 to t= 5730 knowing the Qf/Qi ratio = 1/2
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