MCQ
At a given instant there are $25\%$ undecayed radioactive nuclei in a same. After $10 \,sec$ the number of undecayed nuclei reduces to $6.25\%$, the mean life of the nuclei is...........$ sec$
- A$14.43$
- ✓$7.21$
- C$5$
- D$10$
✓
Answer
Correct option: B.
$7.21$
b
(b) In $10\, sec$, number of nuclei has been reduced to one fourth ($25\%$ to $6.25\%$).
Therefore it’s half life is $T_{1/2} = 5\, sec$.
$\therefore$ Mean life $T = \frac{{{T_{1/2}}}}{{0.693}} = \frac{5}{{0.693}}$ $= 7.21\, sec$.
(b) In $10\, sec$, number of nuclei has been reduced to one fourth ($25\%$ to $6.25\%$).
Therefore it’s half life is $T_{1/2} = 5\, sec$.
$\therefore$ Mean life $T = \frac{{{T_{1/2}}}}{{0.693}} = \frac{5}{{0.693}}$ $= 7.21\, sec$.
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