Thus in either case, whether polar or non-polar, a dielectric develops
a net dipole moment in the presence of an external field The dipole
moment per unit volume is called polarisation and is denoted by P For
linear isotropic dielectrics,
0
P=ε χ
eE
(2 37)
where ce is a constant characteristic of the dielectric and is known as the
electric susceptibility of the dielectric medium