# Exponential Models- Physics B G494

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- Created by: Laura
- Created on: 08-04-13 16:27

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**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.

**Radioactive Decay**

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**…

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