23 Electromagnetic Waves
Principle
Faraday’s law: time-varying B-field creates E-field (emf)
Maxwell: time-varying E-field generates B-field (emf)
EM waves were PREDICTED
by J.C. Maxwell in 1865.
Light is part of the EM wave
James C Maxwell
British Scientist
(1831 – 1879)
Heitz first detected the EM
waves in 1887 after Maxwell
died (1879).
Another great prediction(s)
was made by Einstein from
his General Relativity.
Heinrich R Hertz
German physicist
(1857 –1894)
Properties of EM Waves
1. Transverse Wave; Both E & B
perpendicular to propagation,
k. E, B and k follow the righthand rule
2. EM waves can be created and
travel in vacuum (no medium
required) with unchanging
speed c
3. E & B are in phase and E= cB
c
1
 0 0
(in vacuum)
 3.00108 m / s
v = lf
EM Spectrum
Images Taken in Different EM Wave
Regions
Sinusoidal Waves
 t x
y( x, t )  A sin 2     A sin t  kx
T l 
Energy in EM Waves
1
1
2
u  u E  uB   0 E  0 B 2
2
2
E
B    0 0 E 
c
u   0 E 2 (u E  u B )
1 U uV uAct
S


 cu
A t At
At
S: energy per unit area per unit
time or power per unit area and
the average value, Sav called
intensity, I.
Radiation Pressure
U
p  mc
c
p U u S
   2
V Vc c c
1 p I
Radiation Pressure :

A t c
Nature of Light: Wave-Particle Duality
Wave Fronts
Geometric optics &
Physical Optics
Rays & Waves
Reflection & Refraction
Index of Refraction & Snell’s Law
c
Normal
n
Incident
v
qa
qr
na sin q a  nb sin q b
Reflection
na
nb
qa  qr
qb
Refraction
Angles respect to normal line
All the rays in same plane
Experience: Driving & Reflections
Value of Refractive Index
Air
1.0003
Total Internal Reflection
na
sin qb  sin q a
nb
Critical angle: when qb = 90o,
qa = qc = sin-1(na/nb)
90
qc
Dispersion: n= n(l)
Polarization
Linear polarization
Circular polarization
(left)
Mirage, Blue Sky, & Traffic Lights
Summary: EM Waves, Speed &
Spectrum
Sinusoidal Waves and Energy
Nature of Light
Reflection & Refraction
Total Internal Reflection:
Reflection & Refraction: Animations
Animation of Refraction (rays)
Animation of Refraction (waves)
Dispersion
Polarization
Homework
Ch 23 Problems: 3, 6, 13, 20, 26, 38, 45, and 49
Test III Score Distribution
8
Your grade =points/16x100%
7
Number of Students
6
5
4
3
2
1
0
1
2
3
4
5
6
7
8
9
10
11
Correct Points
12
13
14
15
16
17