Half-Life Practice SET 3

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 mass after a certain number of half-lives?

Back

Remaining mass = Original mass × (1/2)^(number of half-lives).

Front

If a sample has a half-life of 10 years, how much of a 100 g sample remains after 30 years?

Back

After 30 years (3 half-lives), 100 g × (1/2)^3 = 12.5 g remains.

Front

What fraction of a sample remains after 4 half-lives?

Back

1/16 of the original sample remains after 4 half-lives.

Front

If 64 grams of a substance remain after 3 half-lives, what was the original mass?

Back

The original mass was 512 grams.

Front

What happens to the half-life of a substance as it decays?

Back

The half-life remains constant regardless of the amount of substance present.

Front

How long will it take for a 20 g sample of strontium-90 to decay to 5 g?

Back

It will take 2 half-lives (approximately 145.5 years) for the sample to decay to 5 g.

Front

What is the half-life of a substance if 25% of the original sample remains?

Back

The half-life is 2 half-lives.

Front

If a radioactive isotope has a half-life of 5 years, how much of a 40 g sample will remain after 15 years?

Back

After 15 years (3 half-lives), 40 g × (1/2)^3 = 5 g remains.

Front

What is the relationship between half-life and decay rate?

Back

A shorter half-life indicates a faster decay rate.