Electricity and magnetism/Electrostatics/Electrical polarization

A body is electrically polarized when a charge difference appears between two of its points. Conductive bodies are polarized when they are placed in a uniform external electric field. Opposite surface electric charges appear on two opposite sides of the object. Insulating bodies are also polarized by a uniform electric field. Surface electric charges appear on two opposite sides. How is this possible, when by definition, an insulating body has no free electric charges to move? In an insulating body, the electrons are attached to the nuclei. There is no free conduction electron to pass from one nucleus to another. Around the nucleus to which they are attached, the electrons have retained a little mobility. They can concentrate on one side or the other in order to compensate for the external electrical force to which they are subjected. We can think of electrons trapped in an atom or molecule as an electric fluid which is retained by the nuclei and which can be deformed. This is why insulating bodies can be polarized by an electric field like conducting bodies. Inside an insulating body, electric charges are displaced uniformly when it is polarized by a uniform external field. The charge density therefore remains zero inside the material. The surface charge density is the only one that varies. The movement of positive and negative charges inside an insulating body at the moment of its polarization is a transient electric current. But a permanent electric current cannot flow through an insulating material. When a body is electrically polarized, it orients itself in the direction of the applied electrical forces: 400px 400px 400px