If a radioactive element having half-life of $30 \mathrm{~min}$ is undergoing beta decay, the fraction of radioactive element remains undecayed after $90 \mathrm{~min}$. will be
Solution
$t_{\text {half }}=30 \mathrm{~min}$.
<br/><br/>
In 90 min. there will be 3 half lives
<br/><br/>
$$
\begin{aligned}
\text { Number of remaining } & =\left(\frac{N_{0}}{2^{3}}\right) \\\\
& =\frac{N_{0}}{8}
\end{aligned}
$$
<br/><br/>
$\therefore \quad$ Fraction will be $\frac{1}{8}$
About this question
Subject: Physics · Chapter: Atoms and Nuclei · Topic: Radioactivity
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