The table shows the results of an experiment to find the half-life of a radioactive substance.
| Time / minutes | Count rate / (counts / minute) |
|---|---|
| 0 | 400 |
| 10 | 317 |
| 20 | 252 |
| 30 | 200 |
| 40 | 159 |
| 50 | 126 |
What is the half-life of the substance?
10 minutes10\text{ minutes}10 minutes
20 minutes20\text{ minutes}20 minutes
30 minutes30\text{ minutes}30 minutes
40 minutes40\text{ minutes}40 minutes
484 exam-style questions on CIE IGCSE Physics 5.2 Radioactivity, covering 5.2.1 Background radiation and measuring count rate, 5.2.2a Alpha, beta and gamma emission, 5.2.2b Deflection and ionising effects of nuclear radiation, 5.2.3a Radioactive decay, 5.2.3b Effects of decay on the nucleus and decay equations, 5.2.4a Half-life, 5.2.4b Choosing isotopes for applications, and 5.2.5 Effects of ionising radiation and safety precautions. Each one has a worked solution and a mark scheme showing where the marks go.