Black spectral intensity

According to this, the spectral intensity of the black body is independent of direction and is the same as the spectral intensity of hollow enclosure radiation at the same temperature ... 

As shown in 5.1.6, the laws of thermodynamics demand that there must be an upper limit for the spectral intensity Lx(X,(3,(p,T) for all bodies. This maximum emission is associated with an ideal radiator, the black body. Its radiation properties shall be dealt with in the following. 

A black body is defined as a body where all the incident radiation penetrates it and is completely absorbed within it. No radiation is reflected or allowed to pass through it. This holds for radiation of all wavelengths falling onto the body from all angles. In addition to this the black body is a diffuse radiator. Its spectral intensity LXs does not depend on direction, but is a universal function iAs(A,T) of the wavelength and the thermodynamic temperature. The hemispherical spectral emissive power MXs(X,T) is linked to Kirchhoff s function LXs(X,T) by the simple relationship... 

We refrain from deriving the equations for the spectral intensity and the hemispherical spectral emissive power of a black body, found by M. Planck [5.6], for... 

The body has any radiation properties. The spectral irradiance K is independent of direction and is proportional to the spectral intensity of a black body at the temperature of the absorbing surface K = C LXa, T). 

The equality of the three pairs of absorptivities and emissivities, namely ax(X,T) = ex(X,T), a (/3,ip,T) = j3,ip,T) and a(T) = e(T), is only given if the absorbing and emitting surfaces have particular properties, or if the incident spectral intensity Kx of the radiation satisfies certain conditions in terms of its directional and wavelength dependency. These conditions are satisfied by incident black body radiation, when the black body is at the same temperature as the absorbing body, which does not apply for heat transfer. In practice, the more important cases are those in which the directional spectral emissivity e x of the absorbing body at least approximately satisfies special conditions. We will once again summarise these conditions ... 

As an example, consider a sphere of radius R with a black wall of temperature 4 flUed with an isothermal gas at 4, as shown in Figure 7.16. Neglect scattering and assume that the gas has a refractive index of 1 and an absorption coefficient k that is independent of the wavelength (gray assumption). The spectral intensity at the wall is a function of angle 0. From Equation (7.25), we have 4(0) = + 4 j(4)(1-c ). Since k is not a function of the wavelength,... 

The Planck distribution formula describes the spectral intensity of the radiation field from a black body as... 

Xenon has also been applied to the study of humic substances. Previously, there had only been one study on the investigation of surface of soil materials using xenon, namely a study of xenon sorption on to the montmorillonite clay surface. Magusin et al. explored the use of xenon NMR to probe the average volume to area ratio in the pore networks of humidified sand as well as carbon black and kaolin model systems. High-pressure xenon NMR experiments were carried out and showed a broad resonance around 45-55 ppm for three different samples of carbon black with different particle sizes. By comparison, the kaolin and humidified sand showed broad resonances near 8 ppm and zero, respectively. The humidified sand spectrum showed xenon spectral intensity at negative ppm values. The authors derived an expression for the pore size given the measured xenon chemical shift and a constant related to xenon adsorption on the surface. 

The concentration of unpaired spins corresponding to the carbon black only is calculated from the ESR spectral intensity of the broad component line. The relationship between the number of unpaired spins and compounding time is the same for all the NR compounds filled with various carbon blacks. The... 

An irradiated object absorbs some of the radiation and transforms it into heat it becomes warmer relative to its environment. The temperature increase depends on properties specific to the material (e.g., degree of absorption, thermal conductivity) and on the spectral intensity of the impacting radiation. Table 2.10. Surface temperatures increase markedly as coloration changes from white to multicolored to brown and black. On dark colored molded parts in particular, surface temperatures up to 60°C and higher can be measured even in moderate climate zones. Because oxidative degradation reactions are dependent on temperature, accelerated oxidation is expected in dark colored articles [86]. 

Nonblack or nongrey bodies are characterized by wavelength dependence of their spectral emissivity. Let be defined as the temperature of the body corresponding to the temperature of a black body. If the ratio of its radiant intensities at the wavelengths Xi, and Xo equals... 

The Stefan-Boltzmann Law and Wien s Law for black body radiation have been unified into Planck s Law for black body radiation, from which Planck s constant was first introduced. Planck s analysis of the spectral distribution of black body radiation led him to an understanding of the quantisation of energy and radiation and the role of the photon in the theory of radiation. The precise law relates the intensity of the radiation at all wavelengths with the temperature and has the form ... 

Sunlamps A sunlamp is similar to a black lamp, except that a different type of phosphor is used and the lamp envelope transmits UV. Figure 16.5 shows a typical spectral distribution from a commercial sunlamp. The wavelength corresponding to maximum power is shifted to lower wavelengths (— 310 nm), compared to black lamps, and there is significant intensity down to 270 nm. However, the intensity decreases rapidly above 330 nm. The mercury lines can again be seen superimposed on the phosphor fluorescence. 

The depth of color is determined as follows. The carbon black is rubbed with a binder (e.g., linseed-oil) to form a paste which is applied in a thick coat on a glass plate. A colorimeter is used to measure the diffuse reflection of light through the glass. The color depth and hue of the paste can be determined from the intensity and spectral distribution of the diffusely reflected light [4.32]. The color depth can also be determined by visual comparison of the paste with pastes of known blackness under very bright illumination. 

Photolysis rate constant k = 5.2 x 10-3 s-1 for a light intensity corresponding to a 12-h average N02 photolysis rate with a black lamp spectral distribution (Kwok et al. 1992) ... 

The Planck theory of blackbody radiation provides a first approximation to the spectral distribution, or intensity as a function of wavelength, for the sun. The black-body theory is based upon a "perfect" radiator with a uniform composition, and states that the spectral distribution of energy is a strong function of wavelength and is pro portional to the temperature (in units of absolute temperature, or Kelvin), and several fundamental constants. Spectral radiant exitance (radiant flux per unit area) is de fined as ... 

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