Particulate nature of light

If we think in terms of the particulate nature of light (wave-particle duality), the number of particles of light or other electi omagnetic radiation (photons) in a unit of frequency space constitutes a number density. The blackbody radiation curve in Fig. 1-1, a plot of radiation energy density p on the vertical axis as a function of frequency v on the horizontal axis, is essentially a plot of the number densities of light particles in small intervals of frequency space. 

Figure 12.5 The photoelectric effect. Light with photons of energy hc/k approaches from the left, strikes the atoms in the metal, and ejects a photoelectron with a kinetic energy equal to the photon energy minus the work function of the metal. This demonstrates the particulate nature of light.

Photon Another term for a single quantum of light, a name chosen to emphasize the particulate nature of light. 

The linear term (b/xj in Eq. (16) is due to the particulate nature of light and electrons and is usually regarded as the dominant source of noise. Often it is. However, even when care is taken to assure a stable instrument and specimen, c is often about 0.01, so that the quadratic term is the largest for many data points. Repeated measurements of a nominally constant signal, for several different signal strengths, can provide estimates of a, b, and c for use in weighting. 

The Wave Nature of Light The Particulate Nature of Light... 

The sunblocks zinc oxide, titanium dioxide, and iron oxide are inorganic chemicals that are not absorbed into the skin. These substances consist of opaque particles that reflect both visible and ultraviolet light. In addition, zinc oxide blocks virtually the entire UVA and UVB spectrum and thus offers overall protection. The particulate nature of these sunblocks enhances their effectiveness at reflecting sunlight. The smaller the particle size, the greater the surface area available for reflection, and the more effective the sun protection offered by the formulation. 

Electromagnetic radiation, which was previously thought to exhibit only wave properties, seems to show certain characteristics of particulate matter as well. This phenomenon, illustrated in Fig. 12.6, is sometimes referred to as the dual nature of light. 

Dual nature of light the statement that light exhibits both wave and particulate properties. (12.2)... 

In a famous comment in Opticks, a book about the nature of light and colors, Newton proposed to find in specific attractions the explanations for all the reactions studied in chemistry. The principle of attraction could enlighten chemistry, Newton thought, when chemical qualities themselves were treated as special instances of universal forces. In the early eighteenth century, the question of particulate attraction became the special focus of two of Newton s... 

Figure 41. Absorption (A) and circular dichroism (B) spectra of poly-L-glutamic acid, pH 3.85, as a function of particle size, which is achieved by sonication. As particle size increases, the ellipticity and absorption extrema are progressively dampened there is increased light scattering (curve b and c of A), and there is a marked red shifting of the CD extrema and crossover. These are distortions in the spectra due to the particulate nature of the optically active system. Adapted, with permission, from [110].

In the 1800s the wave nature of light and the particulate nature of matter dominated physical explanations of the physical world. Newton s and Maxwell s equations were thought to capture all reality, conferring to it an inescapable, deterministic character. Then, at the end of the nineteenth century numerous experiments were conducted that were not reconciled with these prevailing classical mechanical notions. 

Airborne particulates include dust, fume and aerosols. Many such particles are invisible to the naked eye under normal lighting but are rendered visible, by reflection, when illuminated with a strong beam of light. This is the Tyndall effect and use of a dust lamp provides a simple technique for the rapid assessment of whether a dust is present, its flow pattern, leak sources, the effects of ventilation, etc. More sophisticated approaches are needed for quantitative data. Whether personal, spot or static sampling is adopted will depend upon the nature of the information required. 

The upper limit of gas velocity for particulate expansion is termed the minimum bubbling velocity, umb. Determining this can present difficulties as its value may depend on the nature of the distributor, on the presence of even tiny obstructions in the bed, and even on the immediate pre-history of the bed. The ratio umb/umf, which gives a measure of the degree of expansion which may be effected, usually has a high value for fine light particles and a low value for large dense particles. 

Effects of light on Al and Ti centres in igneous rock were studied by measuring the signal at 100 K by modulation field of 0.5 mT.71 Particulate radiation using H+ and He on silica glass was made to simulate solar wind protons and a-particles in nature.72-73... 

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