Half-life of a substance is 20 , minutes. Wha | vedclass

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(B) Let $N_{0}$ be the initial number of radioactive nuclei.After $33 \%$ decay,the number of undecayed nuclei remaining is $N_{1} = N_{0} - 0.33 N_{0

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(B) Let $N_{0}$ be the initial number of radioactive nuclei.After $33 \%$ decay,the number of undecayed nuclei remaining is $N_{1} = N_{0} - 0.33 N_{0} = 0.67 N_{0}$.After $67 \%$ decay,the number of undecayed nuclei remaining is $N_{2} = N_{0} - 0.67 N_{0} = 0.33 N_{0}$.We observe that $N_{2} \approx \frac{N_{1}}{2}$,since $0.33 N_{0} \approx \frac{0.67 N_{0}}{2}$.By the definition of half-life,the time required for the number of undecayed nuclei to reduce to half of its initial value is exactly one half-life.Therefore,the time taken for the substance to decay from $33 \%$ to $67 \%$ is equal to the half-life of the substance,which is $20 \, minutes$.

Half-life of a substance is $20 \, minutes$. What is the time between $33 \%$ decay and $67 \%$ decay? ................ $minutes$

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