6 - 6. (0K).,radiationcomesfrom .

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6.1 Introduction to Radiation Any matter with temperature above absolute zero (0 K) emits electromagnetic radiation. In a simplified picture, radiation comes from  the constantly changing electromagnetic fields of the oscillating atoms. Electromagnetic radiation can be visualized as waves  traveling at the speed of light. The two prominent characters of the wave are the wavelength ( λ ) and frequency ( ν ). The wavelength  is the distance between crest to crest on the wave. The frequency is related to wavelength by the following:   (Eq. 6.1) where  c  is the speed of light, approximately equal to 3×10 8  m/s in vacuum. The wavelength is measured in units of length, and the  frequency is given in cycles per second ( hertz , Hz). The amount of radiation emitted by a body depends on its temperature, and is proportional to  T 4 . This relation shows that as the  temperature of the object increases, the amount of radiation emitted increases very rapidly. The emitted radiation will travel at the  speed of light until it is absorbed by another body. The absorbing medium can be gas, liquid, or solid. Radiation does not require a  medium to pass through. This is demonstrated by solar radiation which pass through interplanetary space to reach the earth. 6.2 Electromagnetic Spectrum Electromagnetic radiation is categorized into types by their  wavelengths. The types of radiation and the respective wavelength  ranges are shown in  Figure 6.1 . Radiation with shorter wavelengths  are more energetic, evident by the harmful gamma and x-rays on 
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This note was uploaded on 10/23/2011 for the course ENGINEERIN 251 taught by Professor Staff during the Spring '11 term at Bangladesh University of Eng and Tech.

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6 - 6. (0K).,radiationcomesfrom .

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