Thermal Blackbody Radiation

Blackbody Radiation Engineering calculations of thermal radiation from surfaces are best keyed to the radiation characteristics of the blackbody, or ideal radiator. The characteristic properties of a blackbody are that it absorbs all the radiation incident on its surface and that the quality and intensity of the radiation it emits are completely determined by its temperature. The total radiative fliix throughout a hemisphere from a black surface of area A and absolute temperature T is given by the Stefan-Boltzmann law ... 

This is Planck s famous radiation law, which predicts a spectral energy density, p , of the thermal radiation that is fully consistent with the experiments. Figure 2.1 shows the spectral distribution of the energy density p for two different temperatures. As deduced from Equation (2.2), the thermal radiation (also called blackbody radiation) from different bodies at a given temperature shows the same spectral shape. In expression (2.2), represents the energy per unit time per unit area per frequency interval emitted from a blackbody at temperature T. Upon integration over all frequencies, the total energy flux (in units of W m ) - that is, Atot = /o°° Pv Av - yields... 

Thermodynamic considerations show that an ideal thermal radiator, or blackbody, will emit energy at a rate proportional to the fourth power of the absolute temperature of the body and directly proportional to its surface area. Thus... 

Fused quartz transmits 90 percent of the incident thermal radiation between 0.2 and 4 fim. Suppose a certain heat source is viewed through a quartz window. Vhat heat flux in watts will be transmitted through the material from blackbody radiation sources at (a) 800°C, (b) 550°C, (c) 250°C, and (d) 70°C ... 

Blackbody Radiation Engineering calculations involving thermal radiation normally employ the hemispherical blackbody emissive power as the thermal driving force analogous to temperature in the cases of conduction and convection. A blackbody is a theoretical idealization for a perfect theoretical radiator i.e., it absorbs all incident radiation without reflection and emits isotropically. In practice, soot-covered surfaces sometimes approximate blackbody behavior. Let /.V, = /. A... 

Introduction 664 12-2 Thermal Radiation 665 12-3 Blackbody Radiation 667 12-4 Radiation Intensity 673 Solid Angle 674... 

We start this chapter with a discussion of eiectromaguetir. waves and the electromagnetic spectniiii, with particular emphasis on thermal radiation. Then we introduce the idealized blackhody, blackbody radiation, and black-body radiation ftinciion, together with the Sle/ati-Bolizniariii law, Planck s law, and Wien s displacement law. 

Thermal Radiation. The wavelength distribution of an ideal thermal radiation emitter (a blackbody) in a vacuum is given by the Planck distribution function... 

Integration of Eq. 16.22 over all wavelengths gives the total thermal radiation emitted by a blackbody... 

Thermal radiation emitted by a real body has an irregular wavelength dependence (see Ref. 47). The emissivity is defined to relate the emissive power of a real body, e or e, to that of a blackbody ... 

When the squares of the halfwidth Au of the signal curves are plot-tedversus the Rydberg atom flux, a straight line is obtained as expected. This line intersects the (Au) axis at a finite value, from which the number of blackbody photons originally in the cavity can be evaluated. The result (3 + 1) is in reasonable agreement with the value given above. It follows that as the atomic flux decreases the thermal radiation becomes the dominant part of the field [15]. 

A particularly striking example of this is the visible light emission from some porous silicon and silicon nanoparticle structures originally ascribed to photoluminescence but later revealed to be blackbody thermal radiation by careful experimentation (Costa et al. 1998 Roura and Costa 2002). Some very spectrally broad cathodoluminescence spectra published are also likely to be primarily thermal radiation, as discussed in the handbook chapter Cathodoluminescence of Porous Silicon. ... 

Antenna Temperature Theoretical temperature at which a blackbody would emit thermal radiation equivalent to the electrical noise of the antenna. 

Fields in thermal equilibrium can be more generally referred to as thermal radiation. One of the characteristic properties of thermal radiation is that its energy density is only a function of temperature unlike the ideal gas, the number of particles of each kind itself depends on the temperature. Blackbody... 

With the above observations that the chemical potential of thermal radiation is zero, the interaction of a two-level atom with blackbody radiation (which Einstein used to obtain the ratio of the rates of spontaneous and stimulated radiation) can be analyzed in a somewhat different light. If A and A are the two states of the atom, and y is a thermal photon, then the spontaneous and stimulated emission of radiation can be written as... 

The concept of blackbody is determining the basis for describing the radiation properties of real surfaces. The black body denotes an ideal radiative surface which absorb all incident radiation, being a diffuse emitter and emit a maximum amount of energy as thermal radiation for a given wavelength and temperature. The black body can be considered as a perfect absorber and emitter. 

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