JEE Main & Advanced JEE Main Paper (Held On 12 April 2014)

  • question_answer
    A piece of bone of an animal from a ruin is found to have \[^{14}C\] activity of 12 disintegrations per minute per gm of its carbon content. The 14C activity of a living animal is 16 disintegrations per minute per gm. How long ago nearly did the animal die? (Given half life of 14C is t1/2 = 5760 years)   [JEE Main Online Paper ( Held On 12 Apirl  2014 )

    A) 1672 years                          

    B) 2391 years

    C) 3291 years                          

    D) 4453 years

    Correct Answer: B

    Solution :

                    Given, for \[^{14}C\] \[{{A}_{0}}=16\] dis \[{{\min }^{-1}}{{g}^{-1}}\] A = 12 dis\[{{\min }^{-1}}{{g}^{-1}}\] \[{{t}_{1/2}}=5760\]years Now, \[\lambda =\frac{0.693}{{{t}_{1/2}}}\] \[\lambda =\frac{0.693}{5760}\]per year Then, from, \[t=\frac{2.303}{\lambda }{{\log }_{10}}\frac{{{A}_{0}}}{A}\] \[=\frac{2.303}{0.693}{{\log }_{10}}\frac{16}{12}\] \[=\frac{2.303\times 5760}{0.693}{{\log }_{10}}1.333\] \[=\frac{2.303\times 5760\times 0.1249}{0.693}=2390.81\approx 2391\]years.


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