We consider only the
simple situation when the induced dipole
moment is in the direction of the field and
is proportional to the field strength (Substances for which this assumption
is true are called linear isotropic
dielectrics ) The induced dipole moments
of different molecules add up giving a net
dipole moment of the dielectric in the
presence of the external field A dielectric with polar molecules also
develops a net dipole moment in an
external field, but for a different reason