NEET Sample Paper NEET Sample Test Paper-82

  • question_answer
    Decay constant of a radio isotope is \[\lambda \] .If \[{{A}_{1}}\,and\,\,{{A}_{2}}\] be its activity at time \[{{t}_{1}}\,and\,\,{{t}_{2}}\]respectively, the number of nuclei which have decayed during the time \[\left( {{t}_{1}}\,-\,\,{{t}_{2}} \right)\] is

    A)  \[{{A}_{1}}\,-\,{{A}_{2}}\]                 

    B)  \[{{A}_{1}}{{t}_{1}}\,-\,{{A}_{2}}{{t}_{2}}\]

    C)  \[\lambda ({{A}_{1}}-{{A}_{2}})\]                  

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

    Correct Answer: D

    Solution :

    According to question, \[{{A}_{1}}=\lambda {{N}_{1}}\,\,at\,\,time\,\,{{t}_{1}}\] \[{{A}_{2}}=\lambda {{N}_{2}}\,\,at\,\,time\,\,{{t}_{2}}\] \[\therefore \] Number of nuclei decayed in interval \[({{t}_{1}}-{{t}_{2}})\] is \[{{N}_{1}}\lambda -{{N}_{2}}\lambda ={{A}_{1}}-{{A}_{2}}\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,{{N}_{1}}-{{N}_{2}}=\frac{[{{A}_{1}}-{{A}_{2}}]}{\lambda }\]


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