8. Dielectric

In media (note: this is the plural of medium) that are not vacuum, polarisation can occur, leading to the induction of charges near the surface of the dielectric, decreasing the electric field by a factor. This factor is what we call the relative permittivity, or \(\epsilon_r\), while the permittivity is denoted by \(\epsilon=\ \epsilon_r\epsilon_0\).  The relative permittivity can be thought of as the factor by which the original surface charge is reduced by to obtain the effective charge, or in other words,