Page "Electromagnetic field" Paragraph 38

where is the charge density, which can ( and often does ) depend on time and position, is the permittivity of free space, is the permeability of free space, and is the current density vector, also a function of time and position.

The units used above are the standard SI units.

Inside a linear material, Maxwell's equations change by switching the permeability and permittivity of free space with the permeability and permittivity of the linear material in question.

Inside other materials which possess more complex responses to electromagnetic fields, these terms are often represented by complex numbers, or tensors.