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Unformatted text preview: c E B / = 2 2 2 2 1 B E dV dU u + = = for any e.m. field 2 2 E B V U u = = = for e.m. wave Energy density: Intensity: Adt dU S Adt uAdx Adt udV S = = 2 2 EB cB E c cu S = = = = (U energy, V  volume) 2 1 2 2 1 2 2 1 B E cB E c I = = = 2 2 rms rms rms rms B E cB E c I = = = Poynting vector: B E S = Traveling EM waves transport energy. This energy transport can be described as: Power: = A d S P S I Intensity for sinusoidal waves in vacuum: ( 29 ( 29 ( 29 2 2 1 2 cos cos E E t kx B B t kx E E =  = = 7) Energy in electromagnetic waves 7) Electromagnetic momentum flow and radiation pressure c EB c S dt dp A 1 = = Flow rate of EM momentum: (momentum transferred per unit area per unit time) Radiation pressure: = = = = c I c S c I c S dt dp A A F rad 2 2 1 absorbed wave reflected wave Example: Intensity of direct sunlight outside atmosphere is about 1.4 kW/mIntensity of direct sunlight outside atmosphere is about 1....
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This note was uploaded on 02/11/2012 for the course PHYSICS 222 taught by Professor Ogilvie during the Fall '05 term at Iowa State.
 Fall '05
 Ogilvie
 Energy

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