1. Maxwell’s equations in a medium
CGS
Comparing Units
MKS
Maxwell’s equations in a medium
where r and J refer to “free” charge and currents. The electric field E, the displacement field D and the polarization P are related by
For typical optical materials and at non-too-high-field strengths, the polarization
goes linearly with the electric susceptibility of the material, ce .
e = 1 in vacuum
e r = 1 in vacuum

2. Comparing Units, continued MKS
CGS
Comparing Units, continued
MKS
The magnetic induction H, the magnetic field B and the
magnetization, M, are related by
For typical optical materials and at typical optical frequencies, the magnetization is
negligible, so we can write:
Except for at boundaries between different materials, in optical problems there
is no free charge or free current, so finally we can write our “optical Maxwell’s
Equations as shown::
In vacuum, in a plane E&M wave there is a relation between peak electric field and
peak magnetic field:
When |Ep|=1 statvolt/cm,
|Bp|= 1 Gauss
When |Ep|=1 volt/meter,
|Bp|= 1/c = 3.33x10-9 Tesla

3. Comparing Units, continued
CGS
MKS
conversion cm
second gm
erg
esu
statvolt
statvolt/cm
Gauss
esu-cm/cc
l length
t time
m mass
U energy
q charge
V Elec. potential
E electric field
B magnetic field
P polarization
meter
second
kilogram
Joule
Coulomb
Volt
erg/joule = 10-7
esu/Coulomb = 3.33 x 10-9
statvolt/volt = 300
statvolt/cm / volt/m = 3x108
Gauss/Tesla = 10-4