Question detail
A radioactive substance has an initial count rate of 800 counts per minute. After 3 half-lives, what will be the remaining count rate? Use the half life sample context to keep Half-lives and the random nature of radioactive decay distinct from nearby atomic and nuclear radiation ideas.
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Atoms and nuclear radiation
Question
- A. 100 counts per minute (halflives and the random nature)
- B. 1000 counts per minute (halflives and the random nature)
- C. 200 counts per minute (halflives and the random nature)
- D. 400 counts per minute (halflives and the random nature)
Answer
The correct answer is 100 counts per minute (halflives and the random nature).
Explanation
The correct answer is 100 counts per minute (halflives and the random nature). It supports the learning objective: Calculate the count rate or activity remaining after a whole number of half-lives.. The correct answer is 100 counts per minute (halflives and the random nature). It directly supports the learning objective: Calculate the count rate or activity remaining after a whole number of half-lives.. In Half-lives and the random nature of radioactive decay, this is the best option because it matches the specific half life sample context; the other options mix up nearby ideas such as activity, count rate, isotope notation, radiation type, or nuclear-equation changes.
Common mistake
Misunderstanding Half-Life Calculations
Students often confuse the concept of half-life with the total decay time, leading to incorrect calculations of remaining count rate or activity.
To accurately calculate the remaining count rate after a number of half-lives, remember that each half-life reduces the count rate by half. Use the formula: remaining count rate = initial count rate × (0.5)^n, where n is the number of half-lives.
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