A sample of a radioactive isotope emits 12 80012\,80012800 β\betaβ-particles per second. After 15 hours the rate of emission has fallen to 400 β\betaβ-particles per second. What is the half-life of this isotope?
3.0 hours3.0\text{ hours}3.0 hours
5.0 hours5.0\text{ hours}5.0 hours
7.5 hours7.5\text{ hours}7.5 hours
15 hours15\text{ hours}15 hours
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.