JAMB - Physics (2000 - No. 30)
If the fraction of the atoms of a radioactive material left after 120years is 1/64, what is the half-life of the material?
24 years
20 years
10 years
2 years
Paskaidrojums
1/64 is the usual fraction left of any radio active material after 4 half-lives, since 1/64 = (1/2)6
This implies that 6 half lives have elapsed.
Thus 6 half lives = 120 years
∴ 1 half life = 120/6 = 20 years
This implies that 6 half lives have elapsed.
Thus 6 half lives = 120 years
∴ 1 half life = 120/6 = 20 years