JEE Main & Advanced Physics Nuclear Physics And Radioactivity Question Bank Critical Thinking

  • question_answer
    If one starts with one curie of radioactive substance (T1/2 = 12 hrs) the activity left after a period of 1 week will be about 

    A)            1 curie                                     

    B)            120 micro curie

    C)            60 micro curie                      

    D)            8 mili curie

    Correct Answer: C

    Solution :

                1 week » 7 days \[\underline{\tilde{\ }}\] \[7\times 24hrs\underline{\tilde{\ }}\,\ 14\]half lives                    Number of atoms left \[=\frac{No}{{{(2)}^{14}}}\], Activity =\[N\lambda \]                    \ Activity left is \[\frac{1}{{{(2)}^{14}}}\] times the initial                    Þ \[\frac{1}{{{(2)}^{14}}}\times 1\] curie \[=\frac{1}{16384}\times 1\] curie\[\cong \]\[61\times {{10}^{-6}}\] curie                    \[\approx 60\mu \,\]curie. 


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