Transcript Physics 123 “Majors” Section Unit 1

Announcements 1/20/12

Prayer
Review Question (not graded)

In an electro-magnetic wave, the electric and
magnetic fields:
a. are always in phase
b. always have a relative phase shift
c. can have a relative phase shift when
absorption takes place
Reading Quiz

The most important frequency for the optical
properties of a conductor is the:
a. decay frequency, wD
b. plasma frequency, wP
c. reflection frequency, wR
d. resonance frequency, w0
Reading Quiz

In a conductor, the optical properties are
described by a ___________ index of
refraction:
a. totally real
b. totally imaginary
c. partially real and partially imaginary
Metals: complex n
From P&W Fig 2.6 (and HW P2.8…)
Reflectance vs. Wavelength
From Hecht
Plasma frequency
Reading Quiz

The vector that gives the direction of energy
transfer through space in an E-M wave is called
the:
a. Clausius vector
b. flow vector
c. Michelson vector
d. polarization vector
e. Poynting vector
Energy stored in fields (appendix)
Derivation of Poynting Theorem
B
 E  
t
B
(dot with B)  B  (  E )   B 
t
E
E
  B  0 J   0 0
(dot with E )  E  (  B)  0 E  J   0 0 E 
t
t
B  (  E )  
 
1  2
B
2 t
E  (  B)  0 E  J 
 0 0 
Bottom eqn minus top eqn…
E  (  B)  B  (  E )  0 E  J 
  ( E  B)
Multiply both sides by -1/0 …
2
E 

t
 0 0 
2
t
2
 
E2 
 
1  2
B
2 t
   0 E 2 B2
0 

t  2
2 0



Derivation of Poynting Theorem, cont.
   0 E 2 B2
  (E  )  E  J  


0
t  2
20
B
like a flux,
call it S
S 
u field
t



energy density, ufield
 E  J
(J includes both Jfree and Jpolar)
has units of
energy density/time…
call it “dumedium/dt”
S 
u field
t
umedium

t
compare to Eqn of Cont.

 J  
t
Intensity