Download E p

CGS
Comparing Units
MKS
Maxwell’s equations in a medium
B  0
  D  4
E 
H 
 1 B
c t
4
1 D
c
J
c t
B  0
E  
D  
B
t
H  J 
D
t
where  and J refer to “free” charge and currents. The electric field E, the
displacement field D and the polarization P are related by
D  E  4 P
D   0E  P
For typical optical materials and at non-too-high-field strengths, the polarization
goes linearly with the electric susceptibility of the material, ce .
P  ceE
D  (1  4ce ) E
 E
P   0 c eE
D   0 (1  c e ) E
  E
  r 0E
  1 in vacuum
 r  1 in vacuum
CGS
Comparing Units, continued
MKS
The magnetic induction H, the magnetic field B and the
magnetization, M, are related by
H
H  B  4 M
1
0
BM
For typical optical materials and at typical optical frequencies, the magnetization is
negligible, so we can write:
H
HB
1
0
B
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::
B  0
E  0
E 
 1 B
c t
B 
 E
c t
B  0
E  0
E  
B
t
  B   r  0 0
E
t
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
Comparing Units, continued
CGS
MKS
conversion
cm
l length
meter
second
t time
second
gm
m mass
kilogram
erg
U energy
Joule
erg/joule = 10-7
esu
q charge
Coulomb
esu/Coulomb = 3.33 x 10-9
statvolt
V Elec. potential
Volt
statvolt/volt = 300
statvolt/cm
E electric field
statvolt/cm / volt/m = 3x108
Gauss
B magnetic field
Gauss/Tesla = 10-4
esu-cm/cc
P polarization