CourseNotes.57

# CourseNotes.57 - Figure 38 Two Different Representations of...

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Unformatted text preview: Figure 38: Two Different Representations of an Electromagnetic Wave. named because the Poynting vector points in the direction that the wave is traveling in. The Poynting vector is defined as ~ S = 1 μ ~ E × ~ B (52) The direction of the Poynting vector points in the direction that the energy is carried, but the magnitude of the Poynting vector tells us how much power is carried per unit area at that instant. | ~ S | = power area inst Since the E and B fields are related in an EM wave, we can write the magnitude of the Poynting vector as S = 1 μ E 2 As noted before, this is the instantaneous amount of energy carried by the wave. Since the frequency of em waves is typically very high, we are usually more interested in the average amount of energy carried by the wave. This is given by the rms value of the magnitude of the electric field S avg = 1 2 μ E 2 m Not only do electromagnetic waves carry energy, but just like particles they also carry momen- tum. This means that when they are absorbed by objects or reflected by objects, they exert atum....
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