THERMAL RADIATION

Publisher Summary Matter can emit electromagnetic radiation by molecular and atomic agitation. The spectrum of electromagnetic radiation encompasses γ rays, X rays, ultraviolet radiation, light, heat, radio waves, and radar waves. This chapter explores the thermal radiation portion of the spectrum of electromagnetic radiation. Thermal radiation, emitted by the agitation associated with the temperature of matter, is commonly called heat and light. Electromagnetic radiation is generally classified by wavelength, though frequency and wave number are also used. Frequency has the advantage over wavelength of not changing when radiation passes from one medium to another. The emissive power of a blackbody at any wavelength and temperature—called its spectral emissive power—is given by Planck's law. The chapter describes the radiant energy emanating from a blackbody. It focuses on evaluating solar radiation, arriving at a surface on the earth. The chapter explains the distinction between terms expressing quantity of energy and those denoting rate of energy.