For the opposite to the conductors, in these materials it does not have free loads that they can be put into motion with easiness. But the dielectrics also are Constitudos of loaded particles (the electres and the protes). An electric field (external), in the presence of a body insulator, also is modified, even so in different way of what he was a conductor. Let us consider a condenser of plates parallel bars, isolated and loaded with a load Q. Let us full the space enters the plates with an dielectric material, for example, wax, to measure d.d.p now enters the plates of the condenser, we go to see that it diminishes comparing with the situation without wax. However, the stored load does not modify, does not have load movement through the wax layer. Then, the electric field in the condenser diminished due to presence of the wax.
Let us introduce a parameter, called constant dielectric that describes the attenuation of the electric field in the wax layer. Mathematically express in the following way: E= That is, the dielectric constant of a material insulator says how many times weakker are the electric field in this material comparing with the one in the vacuum. As the electric field in the condenser he is homogneo, we can say that the definitive constant through the relation (75) is, of fact, a parameter of the material (in this in case that, of the wax) and does not depend on the geometry or the sizes of the body insulator. Then, the electric field in the material insulator is times weakker of what in the vain emptiness: = This must it the fact of that in a external electric field, the insulator is polarized, that is, appears a induced polarization in the material. Many material insulators are constituted by atoms (or for molecules) that they have not null a dipole moment. As we know, a doublet has trend of to line up itself with the external electric field,