A quantity is subject to exponential decay if it decreases at a rate proportional to its value. Symbolically, this process can be expressed by the following differential equation, where N is the quantity and λ (lambda) is a positive number called the decay constant:
The solution to this equation (see derivation below) is: Exponential rate of change
Here N(t) is the quantity at time t, and N0 = N(0) is the initial quantity, i.e. the quantity at time t = 0.
Read more about Exponential Decay: Solution of The Differential Equation, Applications and Examples