NEET Sample Paper NEET Sample Test Paper-15

  • question_answer A freshly prepared radioactive source of half life 2 hr emits radiation of intensity, which is 64 times the permissible safe level. The minimum time after which it would be possible to work safely with this source is

    A)  6 hr                 

    B)  12 hr

    C)  42 hr                          

    D)  128 hr

    Correct Answer: B

    Solution :

    b.\[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{t/T}}\]or \[\frac{1}{64}={{\left( \frac{1}{2} \right)}^{t/T}}\] or \[{{\left( \frac{1}{2} \right)}^{6}}={{\left( \frac{1}{2} \right)}^{t/T}}\]or \[\frac{t}{T}=6\] \[\therefore \]\[t=6T\]or \[t=6\times 2=12\,hr.\] Hence, the correction option is .

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