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Chapter 33 Solutions_8 - Chapter 33 12. I= P 10 106 W = 2 4...

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Chapter 33 12. The intensity of the signal at Proxima Centauri is I P r = = × × = × 4 10 10 4 4 3 9 46 10 4 8 10 2 6 15 2 29 π π . . . . . W ly m / ly W / m 2 b gc h 17. (a) The average rate of energy flow per unit area, or intensity, is related to the electric field amplitude E m by I E c m = 2 0 2 / μ , so E cI m = = × × × = × 2 2 4 10 2 998 10 10 10 8 7 10 0 7 8 6 2 2 μ π H / m m / s W / m V / m c hc hc h . . . (b) The amplitude of the magnetic field is given by B E c m m = = × × = × 8 7 10 2 998 10 2 9 10 2 8 10 . . . V / m m / s T. (c) At a distance r from the transmitter, the intensity is 2 / 2 , I P r = π where P is the power of the transmitter over the hemisphere having a surface area 2 2 r π . Thus ( ) ( ) 2 2 6 2 3 2 2 m 10 10 W/m 6.3 10 W. P r I 3 = π = π 10×10 × = ×
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