Calculation of the potential distribution around a charge or a current in the presence of three dielectric media using the image method

The general formulae for calculating the potential distribution around an electrostatic point charge in the presence of three different dielectric media, i.e. two semi-infinite media separated by a sheet, are deduced using the image method. The potential is expressed as an infinite series which is shown to be convergent. The number of terms for a reasonable accuracy, for instance 10⁻³, is usually less than 20. An equivalence between the point charge in the presence of three dielectrics and a point current (linear current density) in the presence of three media with different resistivity is introduced.