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 *N _{0} = 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

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