A radioactive isotope has a half-life of 5 years.
A sample gives a count rate of 300 counts/min on a detector.
Which calculation is used to predict the count rate after 15 years?
300×12×12×12300 \times \frac{1}{2} \times \frac{1}{2} \times \frac{1}{2}300×21×21×21
300×12×12×12×12300 \times \frac{1}{2} \times \frac{1}{2} \times \frac{1}{2} \times \frac{1}{2}300×21×21×21×21
300×515300 \times \frac{5}{15}300×155
300×155×12300 \times \frac{15}{5} \times \frac{1}{2}300×515×21
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.