13.Nuclei
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किसी रेडियोऐक्टिव पदार्थ की अर्ध-आयु $10$ मिनट है । यदि आरम्भ में नाभिकों की संख्या $600$ है, तो $450$ नाभिकों के विघटित होने में लगने वाला समय (मिनट में) है

A

$20$

B

$10$

C

$15$

D

$30$

(NEET-2018)

Solution

Number of nuclei remaining,

$N=600-450=150$

According to the law of radioactive decay,

$\frac{N}{N_{0}}=\left(\frac{1}{2}\right)^{\frac{t}{T_{1 / 2}}} ;$ where $N_{0}$ is the number of nuclei initially.

$\therefore \quad \frac{150}{600}=\left(\frac{1}{2}\right)^{\frac{t}{T_{1 / 2}}} ;$ where $T_{1 / 2}=$ half life.

or $\quad\left(\frac{1}{2}\right)^{2}=\left(\frac{1}{2}\right)^{\frac{t}{T_{1 / 2}}}$

$\Rightarrow t=2 T_{10}=2 \times 10$ minutes $=20$ minutes

Standard 12
Physics

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