Need for a “New Physics”
U The nuclear model demonstrated by
Rutherford’s gold foil experiments did not
make sense in terms of the physics known at
the time.
U The “new physics” that was needed to
understand atomic structure grew out of
studies of radiant energy.
U In the 1860s James Clerk Maxwell proposed
that radiant energy is propagated in waves of
fluctuating electric (E) and magnetic (H)
fields.
L Radiant energy is electromagnetic
radiation.
L Maxwell’s electromagnetic hypothesis
was confirmed by Heinrich Hertz in
1887.
Copyright ©2010 Robert L. Carter, Ph.D
Electromagnetic Wave
E
y
z
H
x
E = electric field vector
H = magnetic field vector
Copyright ©2010 Robert L. Carter, Ph.D
Parameters of a Wave
λ
A(+)
A(-)
λ
ν = waves/sec
"observer"
λ = wavelength (m, nm, Å)
ν = frequency (1/sec = s-1 = Hz)
A = amplitude
Intensity is proportional to amplitude squared:
I % A2
Copyright ©2010 Robert L. Carter, Ph.D
Key Equations and Constants
Speed of light in vacuum:
c = 2.9979 × 108 m@s-1
Relationship between ν and λ in vacuum:
ν = c/λ
Wavenumbers (cm-1):
ν̃ = 1/λ
Energy:
E = hν = hc/λ = hcν̃
Planck's constant:
h = 6.626 × 10-34 J@s
Copyright ©2010 Robert L. Carter, Ph.D
The Electromagnetic Spectrum
λ
ν
E
γ rays
λ
10-5 nm 10-1 nm
violet
λ = 390 nm
u.v.
visible
infrared
microwave
radar
t.v.
radio
100 nm
500 nm
10-3 cm
1 cm
1m
10 m
103 m
x rays
indigo
blue
green
yellow
orange
red
λ = 760 nm
Copyright ©2010 Robert L. Carter, Ph.D