Light Terms and Formulae Terms Photon - A quanta of light. Photons are particles that have no mass or charge and travel only at speed c , regardless of medium or reference frame. They have an energy given by E = hν where ν is the frequency of the light to which they correspond, and h = 6.626×10-34 J.s (Planck's constant). We can account for the behavior of light by considering it as consisting of a very large number of photons. In this regime the electromagnetic field appears continuous and the granularity of the light beam is negligible. Poynting vector - Named after John Henry Poynting (1852-1914), this is given by: This is the unit power per area crossing a surface with normal . The direction of is parallel to the direction of the propagation of the light ray. Spherical wave - The linear wave described in Waves is not the only solution to the wave equation. In three-dimensions plane and spherical waves can also exist. In spherical waves, the disturbance of the medium is a function of
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