Phys 0175 - Lecture 34

Phys 0175 - Lecture 34 - Lecture 34 (Apr. 10, 2009):...

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Lecture 34 (Apr. 10, 2009): Electromagnetic waves (cont’d): Energy transport and the Poynting vector Radiation pressure Polarization
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Sinusoidal em waves that represent solutions to the wave equation: E y (x,t)=E max sin(kx-ωt) and B z (x,t)=B max sin(kx-ωt) (a polarized wave propagating in positive x-direction) E max = cB max ω=2πf and k=2π/λ λf = c = 299 792 458 m/s
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The Poynting vector describes both the magnitude and the direction of the energy flow rate of em waves: S has SI units [J/(s•m 2 )]=[W/m 2 ] 0 1 S E B μ = × r r r For a sinusoidal wave, max max max max 0 0 0 1 1 1 2 2 2 av rms rms E B S E B E B = = =
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Intensity of an em wave: Variation of intensity with distance from a point source: (inverse square law) P S = source power ( 29 2 2 2 2 max 0 0 0 energy/time power area area 1 1 1 sin avg avg avg avg rms avg avg I S I S E E kx t E c c c ϖ μ = = = = = = - = 2 4 s P power I area r π = =
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This note was uploaded on 04/06/2009 for the course PHYS 0175 taught by Professor Koehler during the Spring '08 term at Pittsburgh.

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Phys 0175 - Lecture 34 - Lecture 34 (Apr. 10, 2009):...

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