# Solution Exercise 2

Darcy’s law is defined by *q* = –*k*∇*h*, where:

*q* = specific discharge (length/time)

∇*h* = head gradient (length/length)

*K** *= hydraulic conductivity (length/time)

Ohm’s law is defined by *J* = –*σ*∇*V*, where:

*J* = current density (Ampere/length^{2})

∇*V* = voltage gradient (voltage/length)

*σ** *= electrical conductivity (Seimens/length)

The electrical current density quantifies the flow of electric charge and is thus equivalent to the flow of water. Head and voltages are both measures of potential (or energy). Electrical conductivity controls how easily current can flow through the medium, like water with hydraulic conductivity. When combined with conservation of mass or charge, both of these equations become diffusion equations.