Question Detail
Question
The table shows the results of an experiment to find the half-life of a radioactive substance.
| time/hours | count rate from substance (counts/second) |
|------------|---------------------------------------|
| 0 | 800 |
| 1 | 620 |
| 2 | 480 |
| 3 | 370 |
| 4 | 290 |
| 5 | 220 |
What estimate of the half-life of the isotope can be obtained from the readings in the table?
| time/hours | count rate from substance (counts/second) |
|------------|---------------------------------------|
| 0 | 800 |
| 1 | 620 |
| 2 | 480 |
| 3 | 370 |
| 4 | 290 |
| 5 | 220 |
What estimate of the half-life of the isotope can be obtained from the readings in the table?
Correct Answer
Option B is the correct answer.
Detailed Explanation
The half-life of a radioactive substance is the time it takes for its activity (or count rate) to reduce to half of its initial value.Initial count rate at time 0 = 800 counts/second.Half of the initial count rate = 800 / 2 = 400 counts/second.Looking at the table:At 2 hours, the count rate is 480 counts/second.At 3 hours, the count rate is 370 counts/second.Since 400 counts/second is between 480 and 370, the half-life must be between 2 hours and 3 hours.
Hint
The half-life is the time it takes for the count rate to halve. Find when the count rate drops to half its initial value.