..................(2.56)

Therefore, we can summarize the boundary conditions at the surface of a conductor as:

E_t = 0 ........................(2.57)

.....................(2.58)

Behavior of dielectrics in static electric field: Polarization of dielectric  

Here we briefly describe the behavior of dielectrics or insulators when placed in static electric field. Ideal dielectrics do not contain free charges. As we know, all material media are composed of atoms where a positively charged nucleus (diameter ~ 10^-15m) is surrounded by negatively charged electrons (electron cloud has radius ~ 10^-10m) moving around the nucleus. Molecules of dielectrics are neutral macroscopically; an externally applied field causes small displacement of the charge particles creating small electric dipoles.These induced dipole moments modify electric fields both inside and outside dielectric material.