Q 12-13-111JEE MainJEE Main 2021 (27 Aug, Shift 1)Easy
There are $10^{10}$ radioactive nuclei in a given radioactive element. Its half-life time is $1$ min. How many nuclei will remain after $30$ s? $(\sqrt{2} = 1.414)$
Answer: (A) $7\times10^9$
$30$ s is half a half-life:
$$N = N_0\left(\frac{1}{2}\right)^{1/2} = \frac{10^{10}}{1.414} \approx 7\times10^9$$
Solution by Sreeraj P, M.Sc Physics