Electromagnetic Spectrum The Photon and Radiometric Quantities

The photon can be described as the messenger particle for EM force or as the smallest bundle of hght. This subatomic mass less particle comprises radiation emitted by matter when it is excited thermally, or by nuclear processes (fusion, fission), or by bombardment with other radiation. It also can become involved as reflected or absorbed radiation. Photons move at the speed of light 299,792.46 kms. These particles also move as waves and hence, have a dual nature. These waves follow a pattern that we described in terms of a sine (trigonometric) function, as shown in two dimensions (Eig. 2). 

Electromagnetic Spectrum Transmittance, Absorplance, and Reflectance Fig. 3 Eiectromagnetic spectrum trandmittance, Absorptance, and Reflectance 

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