The half life period of a radioactive substance is 60 days. The time taken for $\frac{7}{8}$th of its original mass to disintegrate will be :
Solution
<p>$\because$ $N = {{{N_0}} \over {{2^{{t \over {{T_{1/2}}}}}}}}$</p>
<p>$$ \Rightarrow {2^{{t \over {{T_{1/2}}}}}} = {{{N_0}} \over N} = {{{N_0}} \over {\left( {{{{N_0}} \over 8}} \right)}}$$</p>
<p>$\Rightarrow {2^{{t \over {{T_{1/2}}}}}} = 8 = {2^3}$</p>
<p>$\Rightarrow t = 3 \times {T_{1/2}} = 3 \times 60$</p>
<p>$= 180$ days</p>
About this question
Subject: Physics · Chapter: Atoms and Nuclei · Topic: Radioactivity
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