relative permitivity in a sentence

1. The other parameters represent the following : \ eta the viscosity of the medium; \ lambda the bulk conductivity; \ varepsilon _ { r } the relative permitivity of the medium; \ varepsilon _ { 0 } the permitivity of free space; \ rho the density of the particle; \ rho _ { 0 } the density of the medium; g is the acceleration due to gravity; and ?  " is the electrical conductivity of the bulk electrolyte solution.
2. It's difficult to find relative permitivity in a sentence.