NEET Physics Nuclear Physics And Radioactivity NEET PYQ-Nuclear Physics

  • question_answer
    The half-life of radium is about 1600 years. Of 100 g of radium existing now, 25 g  will remain unchanged after:                                                                                                                                         [AIPMT (S) 2004]

    A)     4800 year  

    B)              6400 year

    C)          2400 year

    D)        3200 year

    Correct Answer: D

    Solution :

    Amount of substance remained is
    \[M={{M}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\]
    Given,
    \[{{M}_{0}}=100\,g;\,\,M=25\,kgm,\,\,{{T}_{1/2}}=1600\] years
    So,       \[25=100{{\left( \frac{1}{2} \right)}^{n}}\]
    or \[\frac{25}{100}={{\left( \frac{1}{2} \right)}^{n}}\]
    or \[{{\left( \frac{1}{2} \right)}^{2}}={{\left( \frac{1}{2} \right)}^{n}}\]
    Comparing the power, we have
    \[n=2\]
    or \[\frac{t}{{{T}_{1/2}}}=2\]
    or \[t=2{{T}_{1/2}}=2\times 1600=3200\] years


You need to login to perform this action.
You will be redirected in 3 sec spinner