Скачать или смотреть Heat radiation. Stefan-Boltzmann law

Heat radiation. Stefan-Boltzmann law.Heat radiation is electromagnetic radiation produced by internal energy of substance. All objects consisting of a large number of atoms produce such radiation at any temperature higher than absolute zero. Apart from that, heat radiation has a continuous spectrum. This means a heated body radiates some amount of energy in every frequency range. The distribution of energy radiated by an object over the spectrum depends on its temperature. With as the temperature of any object increases the amount of energy radiated in the short-wave band of the spectrum also grows. At the same time, the total radiant energy increases. These regularities were discovered in the nineteenth century by means of experiments.According to Stefan-Boltzman radiation law the total energy radiated by a surface area of a black body per 1 second is in proportion to the fourth power of its absolute temperature. That is if the temperature is increased by 2 the intensity of radiation will increase by 16.Stefan-Boltzman law is true for real bodies only in terms of quality. That means the higher the temperature the higher the radiant emittance of any object. However, in reality, the interdependence between the radiant emittance and the temperature of bodies includes the additional factor A. It is the so called integral absorbing capacity of a body.The factor depends on the temperature and is always less than one. Its values have been determined for most important materials used in engineering. For example, factor A of metals varies from 0.1 to 0.4 for a wide range of temperatures and the A factor of coal and metal oxides lies within the range of 0.5 to 0.9.