A dielectric has a molecular concentration of 
. The molecules have
a single resonant frequency of 10GHz.
Use the classical theory of the refractive index to calculate the phase velocity of a 9GHz
electromagnetic wave through the dielectric.
SOLUTION:
From the classical theory of the refractive index:
n is the (complex) refractive index.
N is the molecular concentration.
is the radian resonant frequency of the molecule.
is the radian frequency of the radiation.
is the radiation damping factor:
Using standard terminology:
We show below that using the above figures, the imaginary part of the refractive index is
some 10 orders of magnitude less than the real part. In such case we can write
where 
is the phase velocity at frequency .
Thus:
and n is almost purely real. So we can write:
