JEE Main & Advanced Physics Nuclear Physics And Radioactivity Question Bank Mock Test - Modern Physics

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

    A) \[{{R}_{1}}{{T}_{1}}-{{R}_{2}}{{T}_{2}}\]  

    B) \[{{R}_{1}}-{{R}_{2}}\]

    C) \[\frac{({{R}_{1}}-{{R}_{2}})}{4}\]     

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

    Correct Answer: D

    Solution :

    [d] \[{{T}_{1}}={{N}_{1}}\lambda ,{{R}_{2}}{{N}_{2}}\lambda \] Also \[T=\frac{{{\log }_{e}}2}{\lambda }\] or \[\lambda =\frac{{{\log }_{e}}2}{T}\] \[\therefore {{R}_{1}}-{{R}_{2}}=({{N}_{1}}-{{N}_{2}})\lambda \] \[=({{N}_{1}}-{{N}_{2}})\frac{{{\log }_{e}}2}{T}\] \[\therefore ({{N}_{1}}-{{N}_{2}})=\frac{({{R}_{1}}-{{R}_{2}})T}{{{\log }_{e}}2}\] i.e. \[({{N}_{1}}-{{N}_{2}})\propto ({{R}_{1}}-{{R}_{2}})T\]


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