uminum paint( 铝粉浆): 0.80 to 0.96. ? Emissivity usually increases with temperature . 7 5. Practical source of blackbody radiation ? No actual substance is a blackbody. ? An experimental equivalent of a blackbody is an isothermal enclosure containing a small peephole. 8 6. Laws of blackbody radiation ? Planck ’ s law Varying laws of monochromatic emissive power of blackbody with the wavelengths.(Fig14.1) (14.7) 1 / 51, 2???TC be CW ??? 2 16 1 10 742 .3mW C????K cm C??439 .1 29 FIGURE 14.1 Energy distribution in spectra of blackbodies and gray bodies. 10 ? Because ????? 0 ,dW W bb Stefan-Boltzmann law Total emissive power of a blackbody is proportional to the fourth power of the absolute temperature 4TW b??(14.5) Stefan-Boltzmann constant: 428/ 10 672 .5KmW?????
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