classical physics newton’s laws: newton’s laws: allow prediction of precise trajectory for...
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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.
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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
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Properties of Waves
Frequency () - the number of waves that pass through a particular point in 1 second (Hz = 1 cycle/s).
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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
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Figure 8.2 The Electromagnetic Spectrum
R O Y G B I V
λ
cν
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““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
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Fig 8.4 Experimental representation of a black-body
Capable of absorbing & emitting all frequencies uniformly
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Fig 8.3
The energy distribution in a
black-body cavity at several
temperatures
Stefan-Boltzmann law:
E = aT4
E
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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
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Fig 8.6
Rayleigh-Jeans predicts infinite energy density at short wavelengths:
dkT84dE =
“Ultraviolet catastrophe”
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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.
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Fig 8.10 Typical atomic spectrum:
• Portion of emissionspectrum of iron
• Most compelling evidencefor quantization of energy
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Fig 8.11 Typical molecular spectrum:
Portion of absorptionspectrum of SO2
Contributions from:
Electronic,
Vibrational,
Rotational, and
Translational excitations
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ΔE = hν
ΔE = hc/λ
Fig 8.12 Quantized energy levels
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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
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Fig 8.13 Threshold work functions for metals
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Fig 8.14 Explanation of photoelectric effect
For photons: E ∝ ν
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Fig 8.15 Davisson-Germer experiment
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Fig 8.16 The de Broglie relationship
ph
mvh
Wave-Particle Duality
for:
Light and Matter