Question 139
A half-life is the amount of time that it takes for a radioactive substance to decay one-half of its original quantity.
Suppose radioactive decay causes 300 grams of a substance to decrease 300×2−3 grams after 3 half-lives. Evaluate 300×2−3 to determine how many grams of the substance is left.
Explain why the expression 300×2−n can be used to find the amount of the substance that remains after n half-lives.
Since, 300 g of a substance decreases to 300×2−3g after 3 half-lives.
Similarly, 300 g of a substance would decrease to 300×2−ng after n half-lives.
So, we have to evaluate :
300×2−3
=300×2−3
=3008 [∵23=8]
=37.5 g