# Dictionary:Diffusion equation

**1**. A simplification of the wave equation for EM-waves in a good conductor:

where =angular frequency, =magnetic permeability, and =electric conductivity.

**2**. An equation for the rate of temperature change as a consequence of heat diffusion:

where *T*=temperature, *t*=time, *k*=thermal diffusivity, =density, and *c*_{p}=specific heat at constant pressure. See Fowler (1990, 222–223).