Classical Physics

Newton’s laws:


allow prediction of precise trajectory
for particles, with precise locations and
precise energy at every instant.
allow translational, rotational, and
vibrational modes of motion to be
excited to any energy by controlling
applied forces.
Fig 8.1 Characteristics of electromagnetic waves
Wavelength (l) - distance between identical points on
successive waves.
Amplitude - vertical distance from the midline of a
wave to the peak or trough.
Properties of Waves
Frequency (n) - the number of waves that pass through a
particular point in 1 second (Hz = 1 cycle/s).
Maxwell (1873) proposed that visible light consists
of electromagnetic waves.
Electromagnetic
radiation - emission and
transmission of energy in
the form of
electromagnetic waves.
Speed of light (c) in vacuum = 3.00 x 108 m/s
All electromagnetic
radiation:
c
ν 
λ
Figure 8.2
The Electromagnetic Spectrum
c
ν 
λ
ROYGBIV
“Mysteries” of classical
physics
Phenomena that can’t be explained
classically:
1. Blackbody radiation
2. Atomic and molecular spectra
3. Photoelectric effect
Fig 8.4
Experimental representation
of a black-body
Capable of absorbing & emitting all frequencies uniformly
Fig 8.3
The energy distribution in a
black-body cavity at several
temperatures
Stefan-Boltzmann law:
E = aT4
E
Fig 8.5
The electromagnetic vacuum
supports oscillations of the
electromagnetic field.
Rayleigh For each oscillator:
E = kT
Rayleigh – Jeans law:
dE = ρ dλ
where:

8kT
l4
Fig 8.6
Rayleigh-Jeans predicts
infinite energy density at
short wavelengths:
dE =
8kT
dl
4
l
“Ultraviolet catastrophe”
Fig 8.7
Planck: Energies of the
oscillators are quantized.
The Planck distribution
accounts for experimentally
determined distribution of
radiation.
dE = ρ dλ
8hc

 hc 
5
l [exp
  1]
 lkT 
Fig 8.10 Typical atomic spectrum:
• Portion of emission
spectrum of iron
• Most compelling evidence
for quantization of energy
Fig 8.11 Typical molecular spectrum:
Portion of absorption
spectrum of SO2
Contributions from:
Electronic,
Vibrational,
Rotational, and
Translational excitations
Fig 8.12 Quantized energy levels
ΔE = hν
ΔE = hc/λ
Photoelectric Effect
Solved by Einstein in 1905
hn
Light has both:
KE e-
1. wave nature
2. particle nature
Photon is a “particle” of light
hn = KE + Φ
KE = hn − Φ
Fig 8.13 Threshold work functions for metals
Fig 8.14 Explanation of photoelectric effect
For photons: E
∝ν
Fig 8.15 Davisson-Germer experiment
Fig 8.16 The de Broglie relationship
h
h
l

mv p
Wave-Particle Duality
for:
Light and Matter