Half-Life Calculations-More Practice

Front

What is half-life?

Back

The half-life of a radioactive substance is the time required for half of the radioactive atoms in a sample to decay.

Front

How do you calculate the initial mass of a substance given its remaining mass and half-life?

Back

Use the formula: Initial Mass (M_i) = Remaining Mass (M_f) × 2^(n), where n is the number of half-lives that have passed.

Front

If a substance has a half-life of 5 minutes, how much of a 40 g sample remains after 15 minutes?

Back

After 15 minutes (3 half-lives), 40 g → 20 g → 10 g → 5 g remains.

Front

What is the formula to find the remaining mass after a certain time?

Back

Remaining Mass (M_f) = Initial Mass (M_i) × (1/2)^(t/T), where t is the elapsed time and T is the half-life.

Front

If a sample of 80 g has a half-life of 10 minutes, how much will remain after 30 minutes?

Back

After 30 minutes (3 half-lives), 80 g → 40 g → 20 g → 10 g remains.

Front

What percentage of a substance remains after 2 half-lives?

Back

After 2 half-lives, 25% of the original substance remains.

Front

How do you determine the number of half-lives that have passed?

Back

Divide the total time elapsed by the half-life of the substance.

Front

If a radioactive isotope has a half-life of 20 seconds, how long will it take for a sample to decay to 1/8 of its original mass?

Back

It will take 60 seconds (3 half-lives) to decay to 1/8 of its original mass.

Front

What is the remaining mass of a 100 g sample after 4 half-lives?

Back

After 4 half-lives, 6.25 g remains.

Front

If a substance decays from 50 g to 12.5 g, how many half-lives have passed?

Back

2 half-lives have passed (50 g → 25 g → 12.5 g).