(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 In the absence of any external field, the
different permanent dipoles are oriented
randomly due to thermal agitation; so
the total dipole moment is zero