Characteristics Planck spectrum

For recording of the emission spectrum, the emitted radiation is focussed on the slit of a monochromator and intensities measured attach wavelength. Since sensitivities of photocells or photomultipliers are wavelength dependent, a standardization of the detector-monochromator combination is necessary for obtaining true emission spectrum This can be done by using a standard lamp of known colour temperature whose emission characteristics is obtained from Planck s radiation law. The correction term is applied to the instrumental readings at each wavelength. Very often substances whose emission spectra have been accurately determined in the units of relative quanta per unit wavenumber intervals are... 

The Planck-Kirchhoff law allows a good approximation of the spectral radiance of any thermal radiator, the sources as well as the samples and detectors. Thermal radiators are characterized by a definite temperature as well as by their absorption coefficients f(i>) or a(i>), which describe the characteristic spectrum of the radiator ... 

In 1900 Planck derived an empirical relationship for data from a black body radiation by introducing a concept of quantisation of energy he was able to prove the relationship theoretically. It had been shown that at a specific temperature the spectrum of radiation from a black body was unparalleled in its characteristics and the energy varied... 

The second model of Debye or the Debye-Frohlich model may also be generalized to fractional diffusion [8,25] (including inertial effects [26]). Moreover, it has been shown [25] that the Cole-Cole equation arises naturally from the solution of a fractional Fokker-Planck equation in the configuration space of orientations derived from the diffusion limit of a CTRW. The broadening of the dielectric loss curve characteristic of the Cole-Cole spectrum may then be easily explained on a microscopic level by means of the relation [8,24]... 

Thus, if a transition exists which is related to the frequency of the incident radiation by Planck s constant (h = 6.626-1 O 34), then the radiation can be absorbed. Conversely, if the frequency (v) does not satisfy Planck s expression, then the radiation will be transmitted. A plot of the frequency of the incident radiation against some measure of the percent radiation absorbed by the sample provides the absorption spectrum of the compound or component. The absorption spectrum is characteristic for the compound and this spectrum is often called the fingerprint of the compound. Infrared spectroscopy is based on the measurement of the absorption of electromagnetic radiation that arises from the altering of the vibration level of the component s molecule. An example of the adsorption and transmission of the infrared radiation is shown in Figure 2.30. 

Much of the radiation with which we are familiar in everyday life is of thermal origin, arising by definition from matter in thermal equilibrium. In an ideal atomic gas in thermal equilibrium, for example, the upward versus downward transitions of bound electrons between energy levels in individual atoms are in close balance due to the exchange of energy between particles via collisions and the absorption and emission of radiation. The velocities of particles in an ideal thermal gas follow the well-known Maxwellian distribution, and the collective continuous spectrum of the radiating particles is described by the familiar Planck black-body radiation curve with its characteristic temperature-dependent profile and maximum. 

A minimum in the spectrum occurs at v = 367 cm implying the associated weighting function is maximum near z = 30 km, where the temperature (and hence the Planck intensity) has a minimum. Thus the weighting function and Planck intensity tend to counteract each other, and their product results in the broad, double-peaked contribution function shown in Fig. 4.2.6. In this case the concept of an effective emission level has little meaning, since there exists a broad altitude range over which individual levels contribute about equally to the outgoing intensity. This phenomenon is characteristic of temperature minima... 

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