Models: Models are simplified descriptions of reality, obeying definite rules.
Exponential models: used to describe radioactive decay. Exponential changes are ones in which the rate of change of a quantity is proportional to that quantity- fractional change.
Radioactivity is a random spontaneous process. An exponential equation to describe this process is:
dN/dt = -λN = A
The negative sign is to symbolise that the gradient is negative as the number (N) of atoms we have is decreasing over time. dN/dt represents the activity (A): the number of atoms decaying each second.
If we want to know how many atoms are left, we must use natural logarithms:
N = Noe^-kt…