Half Life Calculations Practice

Front

What is half-life?

Back

Half-life is the time required for half of the quantity of a radioactive substance to decay.

Front

How do you calculate the remaining amount of a substance after a certain number of half-lives?

Back

Remaining amount = Initial amount × (1/2)^(number of half-lives)

Front

If a substance has a half-life of 10 years, how much of a 100 g sample remains after 20 years?

Back

25 g (after 2 half-lives: 100 g -> 50 g -> 25 g)

Front

What happens to the amount of a radioactive substance over time?

Back

It decreases exponentially as it decays over successive half-lives.

Front

If a sample of 8 g of a substance has a half-life of 4 years, how much will remain after 12 years?

Back

1 g (after 3 half-lives: 8 g -> 4 g -> 2 g -> 1 g)

Front

What is the formula to find the number of half-lives that have passed?

Back

Number of half-lives = Total time elapsed / Half-life duration.

Front

If the half-life of a substance is 5 minutes, how long will it take for a 40 mg sample to decay to 5 mg?

Back

20 minutes (4 half-lives: 40 mg -> 20 mg -> 10 mg -> 5 mg)

Front

What is the remaining mass of a 16 g sample after 3 half-lives if the half-life is 2 years?

Back

2 g (16 g -> 8 g -> 4 g -> 2 g)

Front

How do you determine the initial amount of a substance if you know the remaining amount and the number of half-lives?

Back

Initial amount = Remaining amount × 2^(number of half-lives).

Front

If a radioactive isotope has a half-life of 30 minutes, how much of a 12 g sample remains after 90 minutes?

Back

1.5 g (after 3 half-lives: 12 g -> 6 g -> 3 g -> 1.5 g)