Cold body radiation

The emission of light by a body can result from heat for instance iron may glow red-yellow when heated to high temperatures. This is called incandescence. Luminescence is the emission of light by a substance which is not the result of heating. It is a type of cold-body radiation. 

If the vibrational temperature is determined by using the intensities of different bands, a distinct value is obtained for each band. These values do not represent the arithmetic mean of all temperatures. Due to the nonlinear increase of the spectral radiance by the black body radiator, the hot zones appear more pronounced than the cold ones. On the other hand, the influence of the more distant zones with respect to the observer is reduced by stronger self-absorption. The vibrational temperatures deduced from bands with high absorption coefficient are therefore lower than those derived from bands with smaller absorption coefficient. Nevertheless, all thus obtained temperature values are between the lowest and the highest temperature of the sample. The method of fitting calculated spectral profiles to the observed ones has been successfully applied in these cases, too. 

Heat transfer is the passage of thermal energy from a hot body to a cold body. It occurs through conduction, convection, and radiation, or a combination of these. 

In water bodies of sufficient depth, stratification can occur as a result of density differences related to temperature and/or salinity. Stable thermal stratification arises when water warmed by solar radiation (insolation) overlies colder, denser water. At the boundary between the two there is a layer of water in which temperature changes rapidly, termed a thermocline. The associated sharp change in density in the thermocline effectively isolates the warm layer of water from the cold body beneath (Fig. 3.1). 

The thermal energy of the hot source is converted into the energy of electromagnetic waves. These waves travel through space into straight lines and strike a cold surface. The waves that strike the cold body are absorbed by that body and converted back to thermal energy or heat. When thermal radiations falls upon a body, part is absorbed by the body in the form of heat, part is reflected back into space and in some case part can be transmitted through the body. 

In buildings away from outside perimeter walls, air and surface temperatures are usually approximately equal. The heat losses from a person by radiation (q ) and convection (q ) are then flowing to the same temperature level. In such uniform spaces, the radiant and convective losses are about equal and together account for about 80-90% of the total heat loss of a sedentary comfortable individual. In the presence of hot or cold surfaces, as may occur in perimeter or other locations in a building, the average surface temperature of the surroundings (called mean radiant temperature) as seen by the person s body may be substantially different from air temperature. If the mean radiant temperature (MRT) is greater or less than air temperature (T,) the person will feel warmer or colder than in a thermally uniform space where MRT =. ... 

Aside from the general thermal state of the body, a person may find the thermal environment unacceptable or intolerable if local influences on the body from asymmetric radiation, air velocities, vertical air temperature differences, or contact with hot or cold surfaces (floors, machinery, tools, etc.) are experienced. 

We can also notice how, by saying hotter and colder rather than just hot and cold , we can make the law wider in scope. The temperature of a radiator in a living room or lecture theatre is typically about 60 °C, whereas a human body has an ideal temperature of about 37 °C. The radiator is hotter than we are, so heat travels to us from the radiator. It is this heat emitted by the radiator which we absorb in order to feel warmer. 

Universe, tell me how old you are, and 1 will tell you the colour of your radiation background and the energy of each of your photons. Today, the cosmic background radiation is red, very red. It is so red and cold (about 3 K) that it cannot be seen. Its chilled voice quivers in the great ears of our radiotelescopes. Solar emissions, on the other hand, can be compared with the radiation from an incandescent body at a temperature of around 5700 K. Temperatures vary across the Universe, from 2.73 K for the cosmic background to 100 billion K when a neutron star has just emerged. 

Awareness of the obvious overhead heaters, radiators, drafts, leaking roofs, light/heat/cold from windows, metal buildings, black bodies (absorb heat). 

The radiant flux through a spectrometer at a given bandwidth equals = Lj Lj)-G A and B define a black body at higher and lower temperature, re.spectively. A radiant flux flows from the hot to the cold Planck black body, i.e., a radiation source, the sample, or the detector. Combinations of practical significance are listed in Table 3.4-3. 

Similarly, the sense of warmth produced by drinking is deceptive. It is due to increased blood flow to the skin, which allows more heat to radiate to the outside of the body. In fact, inner body temperature is dropping even as the sensation of warmth increases, so that people inadequately dressed for cold weather who drink in order to feel warm may fall victim to hypothermia. 

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