Poynting vectors S is defined as a vector whose magnitude is equal to the wave intensity and whose direction is along the direction of wave propagation. Mathematically, it is given by Show the nature of S vs t graph.


Let the electric and magnetic field by given by equations:


respectively.


Hence, the Poynting vector



Where θ is the angle between the two vectors, and for an electromagnetic wave since the two vectors are always perpendicular, we have θ = 90°,



Hence, S vs t graph is as follows,



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