Question detail

If a radioactive isotope has a half-life of 10 years, how many half-lives will have passed after 40 years?

Try the question, check the answer, then read the explanation to understand the curriculum point.

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At a glance

MCQ

Type

practice

Style

Topic

Atoms and nuclear radiation

Question

A. 2 half-lives
B. 3 half-lives
C. 4 half-lives
D. 5 half-lives

Answer

4 half-lives

Explanation

After 40 years, which is four times the half-life of 10 years, 4 half-lives have passed.

Common mistake

Misunderstanding Half-Life Calculation

Students often confuse the concept of half-life with the total time for decay, thinking it is the time taken for all radioactive nuclei to decay rather than the time for half to decay.

Emphasize that half-life is the time required for half of the radioactive nuclei in a sample to decay, and practice calculating remaining activity after several half-lives.

Related flashcards

Flashcard 1 of 5

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A radioactive substance has a half-life of 5 years. If the initial count rate is 80 counts per minute, what will the count rate be after 15 years? Use the smoke alarm context to keep Half-lives and the random nature of radioactive decay distinct from nearby atomic and nuclear radiation ideas.