What is "half-life"?
Half-life is a term commonly used in radioactivity. It defines the time taken for a radioactive source to halve its activity. A radioactive source will emit radiation (energy) through the emission of particles or photons. How many of these particles are being released every second (or any arbitrary unit of time) determines a substance's activity. This can be seen mathematically through analysing the radioactive decay equations listed in the AQA formula list here: http://filestore.aqa.org.uk/subjects/AQA-PHYA4-5-INS-JUN12.PDF. Furthermore, the maths used to derive the equation for half-life, can be explained through these equations; I would be happy to show you if you wish. In conclusion, half life is how long it takes for a radioactive substance to become half as radioactive as it initially was.
Related Physics A Level answers
All answers ▸Why does light change direction when it hits a surface with a different refractive index?
If photons of wavelength 0.1nm are incident on a 2m x 2m Solar Panel at a rate of 2.51x10^15s^-1, calculate the intensity, I, of the photons on the Solar Panel.
A DVD is dropped from rest. The DVD does not reach terminal velocity before it hits the ground. Explain how the acceleration of the DVD varies from the instant it is dropped until just before it hits the ground.
A small ball is projected with speed 15 m/s at an angle of 60 degrees above the horizontal. Find the distance from the point of projection of the ball at the instant when it is travelling horizontally.