A radioactive isotope has a half-life of 6 hours.
A detector placed near a sample of this isotope measures a count rate of 320 counts per minute. The background count rate is 40 counts per minute.
What is the count rate due to the source after 6 hours?
120 counts per minute120\text{ counts per minute}120 counts per minute
140 counts per minute140\text{ counts per minute}140 counts per minute
160 counts per minute160\text{ counts per minute}160 counts per minute
180 counts per minute180\text{ counts per minute}180 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.