The table shows the results of an experiment to find the half-life of a radioactive substance.
| Time / s\text{s}s | Count rate from substance / counts/second\text{counts/second}counts/second |
|---|---|
| 0 | 200 |
| 40 | 160 |
| 80 | 128 |
| 120 | 100 |
| 160 | 80 |
What is the half-life of the substance?
40 seconds40\text{ seconds}40 seconds
80 seconds80\text{ seconds}80 seconds
120 seconds120\text{ seconds}120 seconds
160 seconds160\text{ seconds}160 seconds
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.