Question 140(i)

Consider a quantity of a radioactive substance. The fraction of this quantity that remains after t half-lives can be found by using the expression $3^{- t}$
What frcation of the substance remains after 7 half-lives?

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Solution

Since $3^{- t}$ expression is used for finding the fraction of the quantity that remains after t half-lives.
Hence, the fraction of substance remains after 7 half-lives will be equal to $3^{- 7}, i . e . \frac{1}{3^{7}} .$

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Question 140(i)

Consider a quantity of a radioactive substance. The fraction of this quantity that remains after t half-lives can be found by using the expression $3^{- t}$
What frcation of the substance remains after 7 half-lives?

Question 140(ii)

Consider a quantity of a radioactive substance. The fraction of this quantity that remains after t half-lives can be found by using the expression $3^{- t}$ .
After how many half-lives will the fraction be $\frac{1}{243}$ of the original?

Question 140(ii)

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 $300 \times 2^{- 3}$ grams after 3 half-lives. Evaluate $300 \times 2^{- 3}$ to determine how many grams of the substance is left.
Explain why the expression $300 \times 2^{- n}$ can be used to find the amount of the substance that remains after n half-lives.

Q. How much quantity of radioactive substance will remain in decayed after 5 half-lives period ?

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Question 140(i) Consider a quantity of a radioactive substance. The fraction of this quantity that remains after t half-lives can be found by using the expression 3−t What frcation of the substance remains after 7 half-lives?

Since 3−t expression is used for finding the fraction of the quantity that remains after t half-lives. Hence, the fraction of substance remains after 7 half-lives will be equal to 3−7, i.e.137.

Question 140(i)

Consider a quantity of a radioactive substance. The fraction of this quantity that remains after t half-lives can be found by using the expression $3^{- t}$
What frcation of the substance remains after 7 half-lives?

Since $3^{- t}$ expression is used for finding the fraction of the quantity that remains after t half-lives.
Hence, the fraction of substance remains after 7 half-lives will be equal to $3^{- 7}, i . e . \frac{1}{3^{7}} .$