Dielectric

Dielectrics (or insulators) are materials where “all charges are attached to specific atoms or molecules.”¹ As opposed to a conductor, dielectrics have a conductivity that approaches 0 ($\sigma =0$). A key implication of this is that within a dielectric, the current density is 0:

$$\vec{J}=0$$

When an electric field passes through a perfect dielectric, the field is weakened compared to that of a vacuum. This is because the applied field polarises some of the dipoles within to oppose some of the field.

Footnotes

1. From Introduction to Electrodynamics, by David Griffiths. ↩