PHYS 422 Lecture 7 EM Theory III

PHYS 422 Lecture 7 EM Theory III - lectromagnetic Theory...

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Unformatted text preview: lectromagnetic Theory Electromagnetic Theory, hotons and Light III Photons, and Light III The Poynting Vector: Polarized Harmonic Wave G B E S G G G = 1 Polarized EM wave: [ ] t r k E E = G G G G cos [ ] t r k B B = G G G G cos t i t Poynting vector: ( ) [ ] t r k B E S = G G G G G 2 cos 1 This is the instantaneous value: S is oscillating Light field oscillates at ~10 15 Hz - most detectors will see the average value of S . Irradiance ( ) [ ] t r k B E S = G G G G G 2 cos 1 We need the average value, over one period, for a harmonic function It can be shown that the average of cos 2 is: ( ) 2 1 cos 2 = T t 2 1 E c B E S = = the average power flow per unit time: 2 2 T g p p Irradiance: Alternative eq-ns: For linear isotropic dielectric: 2 2 E c S I T = T T B c E c I 2 2 = = he Irradiance proportional to the square of the amplitude of the eld T E I 2 v = Usually the E-field component interacts with matter, and we will fer to e ptical eld d use energy uations ith The Irradiance is proportional to the square of the amplitude of the E field refer to E as the optical field and use energy equations with E Optical power radiant flux total power falling on some area (Watts) A Spherical Wave: the Inverse Square Law Spherical waves are produced by point Sp e ca waves a e p oduced by po sources. As you move away from the source the light intensity drops pherical wave uation ( ) ( ) [ ] t r k r t r v cos , A = Spherical wave equation: [ ] t r k r E E = G G G G cos [ ] t r k r B B = G G G...
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This note was uploaded on 03/23/2011 for the course PHYS 422 taught by Professor Staff during the Spring '08 term at Purdue University-West Lafayette.

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PHYS 422 Lecture 7 EM Theory III - lectromagnetic Theory...

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