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
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.