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Math Help - Rather simple question... (What is "time constant"?)

  1. #1
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    Rather simple question... (What is "time constant"?)

    So a math question says "An unspecified quantity of a radioactive element is stored in a safe vault in the year 2000. Six years later, we find there is only half the amount there was originally." one of the subquestions is to find the "TIME CONSTANT..."

    I know how to do these types of questions (radioactive decay and all that jazz) so I don't need the actual answer or any explanations... rather I just need to know what exactly time constant IS. Is it the original quantity when time is zero? Or is it the half-life? Or what? How is it defined?

    Thanks
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  2. #2
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    the following general equation models exponential growth or decay (base e) ...

    A = A_0 e^{kt}

    A = amount of material present at any time t

    A_0 = amount of material at time t = 0

    k is the time constant
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  3. #3
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    Quote Originally Posted by skeeter View Post
    the following general equation models exponential growth or decay (base e) ...

    A = A_0 e^{kt}

    A = amount of material present at any time t

    A_0 = amount of material at time t = 0

    k is the time constant

    Are you sure? I'm pretty certain k is the DECAY constant (because the question asks for both decay constant and time constant)...
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  4. #4
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    not sure ... I do know that k is the time constant when dealing with RC and RL circuits.

    here is a wiki link that seems to explain the difference ...

    http://en.wikipedia.org/wiki/Exponential_decay
    Last edited by skeeter; October 30th 2008 at 03:42 PM.
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