Question

What is the half life of a radioactive substance if
75% of any given amount of the substance
disintegrates in 60 minutes -
​

Answer 1

Explanation:

$75\% \: disintegrates \: means \: 25\% \: remains \: undecayed \: ie \: \frac{1}{4}$

$t = 60min$

$\frac{n}{n0 } \ = \frac{1}{4} \\ = \frac{1}{{2}^{n} } = \frac{1}{ {2}^{2 } } \\ n = 2$

$t = n \: t \frac{1}{2}$

$60 = 2 \times t \frac{1}{2}$

$t \frac{1}{2} = 60 \div 2 = 30 \: min$