lecture24

# lecture24 - Physics 2102 Gabriela Gonzlez A solution to...

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1 Physics 2102 Gabriela González A solution to Maxwell’s equations in free space: ω k = c , speed of propagation. Visible light, infrared, ultraviolet, radio waves, X rays, Gamma rays are all electromagnetic waves. http://phys23p.sl.psu.edu/CWIS/

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2 Electromagnetic waves are able to transport energy from transmitter to receiver (example: from the Sun to our skin). The power transported by the wave and its direction is quantified by the Poynting vector . John Henry Poynting (1852-1914) E B S Units: Watt/m 2 For a wave, since E is perpendicular to B: In a wave, the fields change with time. Therefore the Poynting vector changes too!!The direction is constant, but the magnitude changes from 0 to a maximum value. The average of sin 2 over one cycle is ½ : Both fields have the same energy density. or, A better measure of the amount of energy in an EM wave is obtained by averaging the Poynting vector over one wave cycle. The resulting quantity is called intensity . The total EM energy density is then
3 The light from the sun has an intensity of about 1kW/m 2 . What would be the total power incident on a roof of dimensions 8x20m? I=1kW/m 2 is power per unit area. P=IA=(10 3 W/m 2 ) x 8m x 20m=0.16 MW!! http://us.sunpowercorp.com/homes/products-services/solar-panels/ The solar panel shown (Sunpower E19) is 61in x 41in. The actual solar panel delivers ~6A at 50V.

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## This note was uploaded on 05/20/2011 for the course PHYS 2102 taught by Professor Gimmnaco during the Fall '08 term at LSU.

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lecture24 - Physics 2102 Gabriela Gonzlez A solution to...

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