How does a graph of time to diffuse as a function of distance look? In other words,

1. Use the equation *T = (Δx) ^{2 }/ 2D*

2. Put distance (*Δx*) on the x-axis

3. Put time (*T*) on the y-axis

4. Assume *D* = 0.00001 cm^{2}/sec

So, how does the graph look like?

Remember that** T = (Δx)^{2} / 2D is a quadratic equation**, analogous to

*y = ax*and so takes the shape of a parabola. In this case, the coefficient “

^{2}*a*” is represented by

*1*/(

*2D*). Here is the graph, using

*D*= 0.00001.

Notice that **as the distance increases a little, time increases a lot**. We say that:

- “time to diffuse increases with the square of distance”, or equivalently,
- “distance diffused increases with the square root of time”.