A detector placed near a radioactive isotope gives a measured count rate of 700 counts/minute700\text{ counts/minute}700 counts/minute. The half-life of the isotope is four hours.
The background count rate is 60 counts/minute60\text{ counts/minute}60 counts/minute.
What is the count rate on the detector after twelve hours?
80 counts/minute80\text{ counts/minute}80 counts/minute
140 counts/minute140\text{ counts/minute}140 counts/minute
148 counts/minute148\text{ counts/minute}148 counts/minute
220 counts/minute220\text{ counts/minute}220 counts/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.