Uttarakhand PMT Uttarakhand PMT Solved Paper-2005

  • question_answer
    One gram of [A] decays by p-emission to 0.125 g in 200 years. The half-life period of the reaction is:

    A)  0.014 years       

    B)  6.66 years

    C)  66.6 years        

    D)  666 years

    Correct Answer: C

    Solution :

     Total amount of \[(A)\text{ }{{N}_{0}}=1\text{ }g\] After\[\beta -\] emission the amount rest \[=0.125\text{ }g\] Total time = 200 years \[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{n}},\frac{0.125}{1}={{\left( \frac{1}{2} \right)}^{n}}\] \[=\frac{125}{1000}={{\left( \frac{1}{2} \right)}^{n}}=\frac{1}{8}={{\left[ \frac{1}{2} \right]}^{n}}\] Or \[{{\left( \frac{1}{2} \right)}^{3}}={{\left( \frac{1}{2} \right)}^{n}}n=3\] \[n=\frac{T}{{{t}_{1/2}}},3=\frac{200}{{{t}_{1/2}}}\] \[{{t}_{1/2}}=\frac{200}{3}\] \[=66.6\text{ }years\]


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