Units (Radioactivity)
3 marks · NormalA class is measuring background radiation. The table shows the counts measured in each of three 60-second intervals:
| Interval | Counts |
|---|---|
| 1 | 12 |
| 2 | 14 |
| 3 | 10 |
Calculate the average count per interval.
Calculate the average activity in Bq (counts per second).
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) 12
(b) 0.2 Bq
Common mistakes: using total counts instead of average; not converting time to seconds
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correctly calculates average count: (12+14+10)/3 = 12
M2 (b) · 1 mark · Divides average count by interval time (60 s) to get 12/60 = 0.2 (follow-through)
A1 (b) · 1 mark · Gives final activity in Bq with correct unit (0.2 Bq) (follow-through)
Worked solution
a) Average = (12 + 14 + 10) / 3 = 36 / 3 = 12 counts.
b) Activity = average counts / 60 s = 12 / 60 = 0.2 Bq.