G sin cos t kx z t kx y e e o ω ω r energy and

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e.g., )] sin( ) cos( [ t kx z t kx y E E o ω ω + = ) ) r Energy and momentum in electromagnetic waves: Poynting vector B E c S r r r × = π 4 = flux of energy per unit time through cross-sectional area perpendicular to direction of propagation of the wave=energy/(area-time). S r is in the direction of propagation of the wave Intensity of the wave=I=S av = π π π π 4 4 8 1 8 1 2 2 2 max max max > < = = = E c cE E B E rms Electromagnetic spectrum [from long wavelength (low frequency) to short wavelength (high frequency)]: Radio & TV waves, Microwaves, Infrared, Visible (Red, Orange, Yellow, Green, Blue, Indigo, Violet), Ultraviolet, X-rays, Gamma Rays 2 2 B E and B E r r are both invariant under a Lorentz transformation. “A light wave looks like a light wave in any inertial frame of reference.” Purcell p. 342 Of course, we expect this from the postulates of relativity.
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