1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Modern Physics help.

  1. Feb 7, 2008 #1

    rock.freak667

    User Avatar
    Homework Helper

    1. The problem statement, all variables and given/known data
    Analysis of potassium and argon atoms in a moon rock sample shows that the ratio of the number of stable Ar-40 atoms to the number of radioactive K-40 atoms is 10.3.
    Assume that all the Ar atoms were produces by the decay of K atoms, with a half-life of 1.25x10^ years.
    (i)Calculate:
    a) the fraction of the original K-40 atoms remaining in the rock
    b) the number of half-lives that has elapsed
    c) the age of the rock.

    (ii) From the answers above, deduce the age of the solar system.

    2. Relevant equations

    [tex]N=N_0e^{-\lambda t}[/tex]

    3. The attempt at a solution

    Can someone guide me on how to start this?

    "the number of stable Ar-40 atoms to the number of radioactive K-40 atoms is 10.3."

    Now in the formula N=N_0exp(-[itex]\lambda t[/itex]) N is the no. of radioactive atoms at time t, So I am a bit lost.
     
    Last edited: Feb 8, 2008
  2. jcsd
  3. Feb 7, 2008 #2

    rl.bhat

    User Avatar
    Homework Helper

    If N is the no. of radioactive atoms at time t and N_o is the no. of radioactive atoms at time t = 0, then what is N_o - N? And what is (N_o - N)/N ?
     
  4. Feb 8, 2008 #3

    rock.freak667

    User Avatar
    Homework Helper

    Well [itex]N_0-N[/itex] would be the number of radioactive atoms left at time t.

    But how do I find N_0 or N since I don't have the value of N at t=0 or at any value for t?
     
  5. Feb 11, 2008 #4

    rl.bhat

    User Avatar
    Homework Helper

    (N_0 - N) is the number of stable atoms.
    In the problem (N_0 - N)/N is given. And that is equal to [e^(lambda t)] -1.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Modern Physics help.
  1. Modern Physics (Replies: 4)

Loading...