Chapter 33b - Chapter 33: Electromagnetic Waves ! ! ! ! ! !...

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Ch. 33: Electromagnetic Waves - Part B 1 November 13, 2009 1 Chapter 33: Electromagnetic Waves ! Electromagnetic waves. ! HITT question #1. ! Radiation pressure. ! Polarization. ! HITT question #2. ! Reflection and refraction.
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Ch. 33: Electromagnetic Waves - Part B 2 November 13, 2009 2 The Spectrum of EM Waves ! Maxwell’s rainbow.
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Ch. 33: Electromagnetic Waves - Part B 3 November 13, 2009 3 The Traveling Electromagnetic Wave ! Generation of EM waves ( λ ~ 1m, short-wave radio). ! An LC oscillator produces an AC or oscillatory current at an angular frequency of . ! An external energy source supplies energy to compensate for the thermal loss and the energy carried away by the radiated EM wave. ! The LC oscillator is coupled by a transformer and a transmission line to an antenna. 1/ LC ω=
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Ch. 33: Electromagnetic Waves - Part B 4 November 13, 2009 4 The Traveling Electromagnetic Wave ! For a wave traveling toward point P in the +x direction: sin( ) ω =− ym EE k xt sin( ) zm BB k x t A snapshot of an EM wave. ! ω is the angular frequency, and k is the angular wave number. ! The speed of a wave is . ! The speed of the EM wave is . ! All electromagnetic waves have the same speed c in vacuum. where / ,2 / vk k ωπ λ == m/s 8 00 1/ 3.0 10 c µε × m m E E c
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Ch. 33: Electromagnetic Waves - Part B 5 November 13, 2009 5 Energy Transport ! The rate of energy transport per unit area is described by the Poynting vector S . 0 1 SE B µ ! !! ! The intensity of the EM wave is: Unit is W/m 2 . 22 00 11 2 µµ == = avg rms m IS E E cc power area 2 4 s P I r π (isotropic source with power P s , emitting light at a distance r ) gives the EM wave direction of the travel. ! S
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Ch. 33: Electromagnetic Waves - Part B 6 November 13, 2009 6 Energy Transport Example ! Assume that a TV station acts as a point source broadcasting isotropically at 1.0 MW. What is the intensity of the transmitted signal reaching Proxima Centauri (the star nearest our solar system), 4.3 ly away? 6 29 21 5 2 1.0 10 4.8 10 4 4 ( 4.3 9.46 10 ) ππ × == = × ×× 2 W/m s P I r 1 ly or 1 light-year is the distance light travels in one year.
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This note was uploaded on 03/12/2010 for the course PHY PHY taught by Professor Mueller during the Spring '09 term at University of Florida.

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Chapter 33b - Chapter 33: Electromagnetic Waves ! ! ! ! ! !...

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