Chương này sẽ tóm tắt một số các công thức và định lý liên quan với đen bức xạ. Một điểm nhỏ của phong cách khi từ "đen" được sử dụng như một tính từ, nó là thường được viết như một từ unhyphenated duy nhất, như trong "bức xạ đen", trong khi đó khi "cơ thể" được sử dụng như một danh từ và "đen" như một tính từ, hai từ riêng biệt được sử dụng. Như vậy, một màu đen cơ thể phát ra bức xạ đen. Mặt trời phát ra năng lượng rất gần như một màu đen cơ thể. Bức xạ. | 1 CHAPTER 2 BLACKBODY RADIATION Introduction. This chapter briefly summarizes some of the formulas and theorems associated with blackbody radiation. A small point of style is that when the word blackbody is used as an adjective it is usually written as a single unhyphenated word as in blackbody radiation whereas when body is used as a noun and black as an adjective two separate words are used. Thus a black body emits blackbody radiation. The Sun radiates energy only very approximately like a black body. The radiation from the Sun is only very approximately blackbody radiation. Absorptance and the Definition of a Black Body. If a body is irradiated with radiation of wavelength l and a fraction a l of that radiation is absorbed the remainder being either reflected or transmitted a l is called the absorptance at wavelength l . Note that l is written in parentheses to mean at wavelength l not as a subscript which would mean per unit wavelength interval . The fractions of the radiation reflected and transmitted are respectively the reflectance and the transmittance. The sum of the absorptance reflectance and transmittance is unity unless you can think of anything else that might happen to the radiation. A body for which a l 1 for all wavelengths is a black body. A body for which a has the same value for all wavelengths but less than unity is a grey body. Caution We may meet the word absorbance later. It is not the same as absorptance. Radiation within a cavity enclosure. Consider two cavities at the same temperature. We ll suppose that the two cavities can be connected by a door that can be opened or closed to allow or to deny the passage of radiation between the cavities. We ll suppose that the walls of one cavity are bright and shiny with an absorptance close to zero and the walls of the other cavity are dull and black with an absorptance close to unity. We ll also suppose that because of the difference in nature of the walls of the two cavities the .
