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Unformatted text preview: c E B / = 2 2 2 2 1 μ ε B E dV dU u + = = for any e.m. field 2 2 E B V U u ε μ = = = for e.m. wave Energy density: Intensity: Adt dU S ≡ Adt uAdx Adt udV S = = 2 2 μ μ ε EB cB E c cu S = = = = (U – energy, V - volume) 2 1 2 2 1 2 2 1 μ μ ε B E cB E c I = = = 2 2 μ μ ε rms rms rms rms B E cB E c I = = = Poynting vector: μ 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 = - =- = ϖ ϖ 7) Energy in electromagnetic waves 7) Electromagnetic momentum flow and radiation pressure c EB c S dt dp A 1 μ = = Flow rate of EM momentum: (momentum transferred per unit area per unit time) Radiation pressure: = = = = ≡ Ρ 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 12/10/2011 for the course PHYSICS 222 taught by Professor Frishman during the Spring '11 term at Iowa Central Community College.
- Spring '11