Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

End Amt =Start Amt *e^-0.0391 * t (in years) Half-life =?

  1. Apr 29, 2016 #1
    I know how to do half life problems and I even have a half-life calculator on my website:
    http://www.1728.org/halflife.htm

    However, I cannot calculate half-life when problems are stated in this form:
    End Amt = Start Amt * e^-0.0391 * t (in years)
    Half-life =?

    I know calculus but I find it difficult understanding that kind of equation.

    I believe the figure 0.0391 is the function "lambda".
    So if lambda = .0391
    then
    half-life = ln(2) / lambda
    half-life = 0.6931 / 0.0391
    half-life = 17.73 years
    Did I get that right?
     
  2. jcsd
  3. Apr 29, 2016 #2

    Ygggdrasil

    User Avatar
    Science Advisor

    The half life is the value of t for which End Amt = 0.5 * Start Amt.
     
  4. Apr 29, 2016 #3
    End Amt = Start Amt * e^-0.0391 * t (in years)
    So the equation becoames
    .5 = 1.0 * e^-0.0391 * t
    Taking logs of both sides
    ln (.5) = -0.0391 * t (since ln (e) = 1)
    t = ln (.5) / -0.0391
    t = -0.6931471806/ -0.0391
    t = 17.73 years
    which is what I calculated when using the "lambda" function
    So I guess that is it.
    Thank you. :-)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: End Amt =Start Amt *e^-0.0391 * t (in years) Half-life =?
  1. Half life (Replies: 1)

  2. Half Life Accuracy? (Replies: 20)

Loading...