Which statement correctly describes the term half-life for a radioactive isotope?
The time taken for the number of unstable nuclei in a sample to decrease to a quarter of its original value.
The time taken for the activity of a sample to decrease to half of its initial value.
Half of the time required for all the radioactive nuclei in the sample to decay completely.
The average lifetime of a single radioactive nucleus.
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.