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half-lives for a curve

  1. #1
    im_1
    Guest

    half-lives for a curve

    can someone tell me asap how i can calculate half lives for a curve in
    microsoft excel?

  2. #2
    James Silverton
    Guest

    Re: HALF-LIVES FOR A CURVE

    im_1 wrote on Sun, 27 Nov 2005 10:55:03 -0800:

    i> can someone tell me asap how i can calculate half lives for
    i> a curve in microsoft excel?

    More explanation please? I know about half lives of isotopes and
    reactions but not of curves.

    James Silverton.


  3. #3
    B. R.Ramachandran
    Guest

    RE: HALF-LIVES FOR A CURVE

    Hi,

    Do you mean by 'half-life of a CURVE', the x-value when the y-value is 50%
    of the initial y-value (i.e., y-value when x is zero)? Also, I assume that
    your x-axis corresponds to time.

    If the curve corresponds to an exponential decay of something, i.e., the
    equation for the curve is "y= a*exp(-b*x)" where y is the quantity of that
    thing and x is time, and if you know the values of the parameters ('a' and
    'b'), the half-life ican be calculated using the following equation,

    half-life = ln(2)/b = 0.6931/b

    Note: For an exponential-decay as the above, a plot of ln(y) vs x would be
    linear with a slope of -b and a y-intercept of ln(a).

    If the decay is non-exponential the formula is different. If the functional
    form is known (maybe from the trendline equation of an appropriate type), you
    can calculate the half-life either analytically using an appropriate formula
    or find it using the "Solver" in Excel. Please post details about the
    functional form of the curve.

    Regards,
    B. R. Ramachandan


    "im_1" wrote:

    > can someone tell me asap how i can calculate half lives for a curve in
    > microsoft excel?


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