Manipal Medical Manipal Medical Solved Paper-2008

  • question_answer
    The radioactivity of a sample is\[{{A}_{1}}\]at time\[{{t}_{1}}\]and \[{{A}_{2}}\]at time\[{{t}_{2}}\]. If the mean life of the specimen is T, the number of atoms that have disintegrated in the time interval of\[({{t}_{2}}-{{t}_{1}})\]is

    A)  \[({{A}_{1}}-{{A}_{2}})\]

    B)  \[\frac{({{A}_{1}}-{{A}_{2}})}{T}\]

    C)  \[({{A}_{1}}-{{A}_{2}})T\]

    D)  \[({{A}_{1}}{{t}_{1}}-{{A}_{2}}{{t}_{2}})\]

    Correct Answer: C

    Solution :

     \[{{A}_{1}}={{N}_{1}}\lambda ,\] \[{{A}_{2}}={{N}_{2}}\lambda \] Mean life, \[T=\frac{1}{\lambda }\] \[{{A}_{1}}-{{A}_{2}}=({{N}_{1}}-{{N}_{2}})\lambda \] \[=({{N}_{1}}-{{N}_{2}})\frac{1}{T}\] So, number of atoms disintegrated in\[({{t}_{2}}-{{t}_{1}})s\] \[=({{N}_{1}}-{{N}_{2}})=({{A}_{1}}-{{A}_{2}})T\]


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