First slide

Radio activity

Question

Certain radio active substance reduces to 25% of its initial value in 16 days. Its half life is

Easy

A

32 days
B

8 days
C

64 days
D

28 days

Solution

(2)
$\begin{array}{l} N = \frac{N_{0}}{{(2)}^{t / t 1 / 2}} \Rightarrow \frac{N_{0}}{4} = \frac{N_{0}}{{(2)}^{t / t 1 / 2}} \\ ∴ {(2)}^{t / t 1 / 2} = {(2)}^{2} \Rightarrow \frac{t}{t^{1 / 2}} = 2 \\ \Rightarrow t_{1 / 2} = \frac{7}{2} = \frac{16}{2} d a y s = 8 d a y s \end{array}$

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