atkins chapter8.lect01

7/30/2019 Atkins Chapter8.Lect01

1/20

Classical Physics

Newtons laws:

allow prediction of precise trajectoryfor particles, with precise locations andprecise energy at every instant.

allow translational, rotational, andvibrational modes of motion to beexcited to any energy by controllingapplied forces.


2/20

Wavelength(l) - distance between identical points onsuccessive waves.

Ampl i tude- vertical distance from the midline of a

wave to the peak or trough.

Fig 8.1 Characteristics of electromagnetic waves


3/20

Properties of Waves

Frequency(n) - the number of waves that pass through aparticular point in 1 second (Hz = 1 cycle/s).


4/20

Maxwell (1873) proposed that visible light consists

of electromagnetic waves.

Electromagnet ic

radiat ion- 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


5/20

Figure 8.2 The Electromagnetic Spectrum

R O Y G B I V

c


6/20


7/20

Mysteries of classical

physics

Phenomena that cant be explained

classically:

1. Blackbody radiation

2. Atomic and molecular spectra3. Photoelectric effect


8/20

Fig 8.4 Experimental representationof a black-body

Capable of absorbing & emitting all frequencies uniformly


9/20

Fig 8.3

The energy distribution in a

black-body cavity at several

temperatures

Stefan-Boltzmann law:

E = aT4E


10/20

Fig 8.5

The electromagnetic vacuum

supports oscillations of the

electromagnetic field.

Rayleigh -

For each oscillator:

E = kT

Rayleigh

Jeans law:

dE = d

where: 4

kT8

l


11/20

Fig 8.6

Rayleigh-Jeans predicts

infinite energy density atshort wavelengths:

ll

dkT84

dE =

Ultraviolet catastrophe


12/20

Fig 8.7

The Planck distribution

accounts for experimentallydetermined distribution ofradiation.

dE = d

]1

kT

hc[exp

hc8

5

l

Planck: Energies of the

oscillators are quantized.


13/20

Fig 8.10 Typical atomic spectrum:

Portion of emission

spectrum of iron

Most compelling evidencefor quantization of energy


14/20

Fig 8.11 Typical molecular spectrum:

Portion of absorption

spectrum of SO2

Contributions from:

Electronic,

Vibrational,

Rotational, and

Translational excitations


15/20

E = hE = hc/

Fig 8.12 Quantized energy levels


16/20

Light has both:

1. wave nature

2. particle nature

hn = KE +

Photoelectric Effect

Photonis a particle of light

KE = hn

hn

KE e-

Solved by Einstein in 1905


17/20

Fig 8.13 Threshold work functions for metals


18/20

Fig 8.14 Explanation of photoelectric effect

For photons: E


19/20

Fig 8.15 Davisson-Germer experiment


20/20

Fig 8.16 The de Broglie relationship

ph

mvh

Wave-Particle Duality

for:

Light andMatter

atkins chapter8.lect01

Documents