A student investigates four different radioactive isotopes. The student places a detector near each radioactive material. The background count rate is 24 counts per minute24\text{ counts per minute}24 counts per minute throughout the investigation. The table shows the detector readings at the start and after 6 hours6\text{ hours}6 hours.
| Isotope | Count rate at the start (counts per minute) | Count rate after 6 hours6\text{ hours}6 hours (counts per minute) |
|---|---|---|
| A | 120 | 30 |
| B | 184 | 64 |
| C | 224 | 100 |
| D | 304 | 59 |
Which isotope has a half-life of 3 hours3\text{ hours}3 hours?
A
B
C
D
144 exam-style questions on CIE IGCSE Physics 5.2.4a Half-life. Each one has a worked solution and a mark scheme showing where the marks go.