Classical PhysicsClassical Physics

Newton’s laws:Newton’s laws:

allow prediction of allow prediction of preciseprecise trajectory trajectory for particles, with for particles, with precise locationsprecise locations and and precise energyprecise energy at every instant. at every instant.

allow translational, rotational, and allow translational, rotational, and vibrational modes of motion to be vibrational modes of motion to be excited to excited to any energyany energy by controlling by controlling applied forces.applied forces.

Wavelength () - distance between identical points on successive waves.

Amplitude - vertical distance from the midline of a wave to the peak or trough.

Fig 8.1 Characteristics of electromagnetic waves

Properties of Waves

Frequency () - 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:

λ

cν

Figure 8.2 The Electromagnetic Spectrum

R O Y G B I V

λ

cν

““Mysteries” of classical Mysteries” of classical physicsphysics

Phenomena that can’t be explained Phenomena that can’t be explained classically: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: 4

kT8

Fig 8.6

Rayleigh-Jeans predicts infinite energy density at short wavelengths:

dkT84dE =

“Ultraviolet catastrophe”

Fig 8.7

The Planck distribution accounts for experimentallydetermined distribution ofradiation.

dE = ρ dλ

]1kThc

[exp

hc8

5

Planck: Energies of the

oscillators are quantized.

Fig 8.10 Typical atomic spectrum:

• Portion of emissionspectrum of iron

• Most compelling evidencefor quantization of energy

Fig 8.11 Typical molecular spectrum:

Portion of absorptionspectrum of SO2

Contributions from:

Electronic,

Vibrational,

Rotational, and

Translational excitations

ΔE = hν

ΔE = hc/λ

Fig 8.12 Quantized energy levels

Light has both:

1. wave nature2. particle nature

h = KE + Φ

Photoelectric Effect

Photon is a “particle” of light

KE = h − Φ

h

KE e-

Solved by Einstein in 1905

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

ph

mvh

Wave-Particle Duality

for:

Light and Matter