The conductivity of plasma can be related to its microscopic properties using the Drude model
where is the number density, is the elementary charge, is the mass of the electron and is the collision rate. The latter is given by
where is the cross section for collisions and is the thermal velocity. To calculate the cross section, we note the impact parameter below which a scattering angle between an electron and a proton will be of order unity
Finally, the resistivity is given by
where is the temperature and is the Boltzmann constant.