Half-Life Practice

Front

What is half-life?

Back

Half-life is the time required for half of the radioactive atoms in a sample 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 number of radioactive atoms in a sample over time?

Back

The number of radioactive atoms decreases exponentially over time.

Front

If you start with 80 g of a substance with a half-life of 5 years, how much will remain after 15 years?

Back

10 g (after 3 half-lives: 80 g -> 40 g -> 20 g -> 10 g)

Front

What is the half-life of carbon-14?

Back

The half-life of carbon-14 is approximately 5730 years.

Front

How many half-lives are needed for a substance to decay from 64 g to 8 g if its half-life is 10 years?

Back

3 half-lives (64 g -> 32 g -> 16 g -> 8 g)

Front

If a radioactive isotope has a half-life of 1 year, how much of a 16 g sample will remain after 3 years?

Back

2 g (after 3 half-lives: 16 g -> 8 g -> 4 g -> 2 g)

Front

What is the relationship between half-life and the stability of a radioactive isotope?

Back

Shorter half-lives indicate less stability and faster decay.

Front

If you have 1,000 atoms of a radioactive isotope with a half-life of 2 years, how many will remain after 6 years?

Back

125 atoms (after 3 half-lives: 1000 -> 500 -> 250 -> 125)