The background count rate measured by a radiation counter is 80 counts per minute80\text{ counts per minute}80 counts per minute. With the counter close to a radioactive source, the counter reading is 1040 counts per minute1040\text{ counts per minute}1040 counts per minute. The half-life of the source is 15 minutes15\text{ minutes}15 minutes. What is the counter reading 45 minutes45\text{ minutes}45 minutes later?
120 counts per minute120\text{ counts per minute}120 counts per minute
130 counts per minute130\text{ counts per minute}130 counts per minute
200 counts per minute200\text{ counts per minute}200 counts per minute
210 counts per minute210\text{ counts per minute}210 counts per minute
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.