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

so

Finally, the resistivity is given by

where is the temperature and is the Boltzmann constant.