A method for calculating the radiation power coefficients of black and gray bodies with dimensions commensurable with the radiated wavelengths
A technique is proposed and the calculations of the dependences of the emissivity of an absolute black body (BBB) on the size of the diaphragms of the emitting aperture are performed for hypothetical cases when the sizes of the diaphragms are commensurate with the emitted wavelengths, and the diaphragms are made of a dielectric opaque for radiation. The value of the cutoff wavelength l = 1.772´A for the square aperture of the diaphragm was determined, where A is the side of the square and l = 1. 571´D for the round hole. where D is the hole diameter, i.e. it is shown that the body cannot emit wavelengths λ greater than 1.772´A in the case of a square hole and 1.571´D in the case of a round hole. It is shown that if the “cut off” wavelengths made any significant contribution to the integral radiation of a blackbody with temperature T at standard diaphragm diameters (i.e., at diameters of much larger radiated wavelengths), then the emissivity of this body becomes less than unity and rapidly decreases when the size of the diaphragms is commensurate with l. In these cases, such a body ceases to be an absolutely black body and the laws of Planck and Stefan-Boltzmann cannot be used to calculate the power of its radiation, but the technique proposed in this work can be used.