First slide

Radio activity

Question

A radioactive substance has a half life of 60 minutes After 3hours, the fraction of atom that have decayed would be

Moderate

A

12.5%
B

87.5%
C

8.5%
D

25.1%

Solution

$N = N_{0} {(\frac{1}{2})}^{\frac{t}{T_{1 / 2}}}$
Hence, fraction of atom decayed
$= 1 - \frac{N}{N_{0}} = 1 - {(\frac{1}{2})}^{\frac{t}{T_{1 / 2}}} = 1 - {(\frac{1}{2})}^{\frac{3 x 60}{60}} = \frac{7}{8} In percentage it is \frac{7}{8} x 100 = 87.5 %$

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