J & K CET Medical J & K - CET Medical Solved Paper-2006

  • question_answer
    A radioactive substancc has a half-life of four months. Three-fourth of the substance will decay in :

    A)  3 months                           

    B)  4 months

    C)  8 months                           

    D)  12 months

    Correct Answer: C

    Solution :

                     From Rutherford-Soddy?s law \[N={{N}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\] Given, \[N=1-\frac{3}{4}=\frac{1}{4}{{N}_{0}},n=\frac{t}{T}=\frac{t}{4}\] \[\therefore \]  \[\frac{1}{4}={{\left( \frac{1}{2} \right)}^{t/4}}\] \[\Rightarrow \]               \[{{\left( \frac{1}{2} \right)}^{2}}={{\left( \frac{1}{2} \right)}^{t/4}}\] \[\Rightarrow \]               \[2=\frac{t}{4}\] \[\Rightarrow \]               \[t=8\text{ }months\]


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