Which of the following is a correct definition of the half-life of a radioactive isotope?
The time taken for the total mass of the sample containing the isotope to be reduced by half.
Half of the time taken for all of the radioactive nuclei in a sample to decay.
The time taken for the number of radioactive nuclei of that isotope in a sample to decrease to half of its initial value.
The time taken for the activity of the sample to decrease to zero.
484 exam-style questions on CIE IGCSE Physics 5.2 Radioactivity, covering 5.2.1 Background radiation and measuring count rate, 5.2.2a Alpha, beta and gamma emission, 5.2.2b Deflection and ionising effects of nuclear radiation, 5.2.3a Radioactive decay, 5.2.3b Effects of decay on the nucleus and decay equations, 5.2.4a Half-life, 5.2.4b Choosing isotopes for applications, and 5.2.5 Effects of ionising radiation and safety precautions. Each one has a worked solution and a mark scheme showing where the marks go.